Jane Austen’s Paper Trail is a podcast from The Conversation celebrating 250 years since the author’s birth. In each episode, we investigate a different aspect of Austen’s personality by interrogating one of her novels with leading researchers. Along the way, we visit locations important to Austen to uncover a particular aspect of her life and the times she lived in.
For episode seven of Jane Austen’s Paper Trail, we’re doing something a little different. Rather than putting Austen under the microscope ourselves, we’re handing the questions over to you.
Jane Austen is a curious author because the more we learn about her, the more elusive she seems to become. She left behind a remarkably slim paper trail for someone so influential, and much of what we “know” about her has been filtered through family memory, biography and, sometimes, wishful thinking. As Jane Austen’s Paper Trail draws to a close, there are still loose ends to tie up – and that’s where you, our listeners, come in.
We’ve received a virtual sack full of letters from you, ranging from questions about Austen’s religious beliefs to her grasp of contemporary science, and even what she might have made of social media. Unlike Jane’s sister Cassandra Austen, however, we have no intention of throwing your letters into the flames. Instead, three experts join me to debate them – and, where possible, to settle them.
For our first panellist, we’re welcoming back Emma Claire Sweeney from episode four about Austen’s friendships. Sweeney is a senior lecturer in creative writing at the Open University and worked collaborated on a interactive experience with the BBC as part of the Jane Austen: Rise of a Genius.
Returning from episode six about whether Austen was happy is John Mullan, professor of literature at University College London and author of What Matters in Jane Austen. Completing the panel is Lizzie Dunford, director of Jane Austen’s House in Hampshire.
Together, they take your questions seriously, testing what can be answered from the novels, what can be inferred from historical context, and where Austen herself remains stubbornly silent. From faith and feminism to fame and future technology, these questions remind us why Austen continues to fuel our curiosity 250 years after her birth.
Jane Austen’s Paper Trail is hosted by Anna Walker with reporting from Jane Wright and Naomi Joseph. Senior producer and sound designer is Eloise Stevens and the executive producer is Gemma Ware. Artwork by Alice Mason and Naomi Joseph.
Listen to The Conversation Weekly via any of the apps listed above, download it directly via our RSS feed or find out how else to listen here.
A great white shark is a masterwork of evolutionary engineering. These beautiful predators glide effortlessly through the water, each slow, deliberate sweep of the powerful tail driving a body specialised for stealth, speed and efficiency. From above, its dark back blends into the deep blue water, while from below its pale belly disappears into the sunlit surface.
In an instant, the calm glide explodes into an attack, accelerating to more than 60 kilometres per hour, the sleek torpedo-like form cutting through the water with little resistance. Then its most iconic feature is revealed: rows of razor-sharp teeth, expertly honed for a life at the top of the food chain.
Scientists have long been fascinated by white shark teeth. Fossilised specimens have been collected for centuries, and the broad serrated tooth structure is easily recognisable in jaws and bite marks of contemporary sharks.
But until now, surprisingly little was known about one of the most fascinating aspects of these immaculately shaped structures: how they change across the jaw and to match the changing demands throughout the animal’s lifetime. Our new research, published in Ecology and Evolution, set out to answer this.
From needle-like teeth to serrated blades
Different shark species have evolved teeth to suit their dietary needs, such as needle-like teeth for grasping slippery squid; broad, flattened molars for crushing shellfish; and serrated blades for slicing flesh and marine mammal blubber.
Shark teeth are also disposable – they are constantly replaced throughout their lives, like a conveyor belt pushing a new tooth forward roughly every few weeks.
White sharks are best known for their large, triangular, serrated teeth, which are ideal for capturing and eating marine mammals like seals, dolphins and whales. But most juveniles don’t start life hunting seals. In fact, they feed mostly on fish and squid, and don’t usually start incorporating mammals into their diet until they are roughly 3 metres long.
This raises a fascinating question: do teeth coming off the conveyor belt change to meet specific challenges of diets at different developmental stages, just as evolution produces teeth to match the diets of different species?
Previous studies tended to focus on a small number of teeth or single life stages. What was missing was a full, jaw-wide view of how tooth shape changes – not just from the upper and lower jaw, but from the front of the mouth to the back, and from juvenile to adult.
An array of jaws from sharks ranging from 1.2m to 4.4m. Emily Hunt
Teeth change over a lifetime
When we examined teeth from nearly 100 white sharks, clear patterns emerged.
First, tooth shape changes dramatically across the jaw. The first six teeth on each side are relatively symmetrical and triangular, well suited for grasping, impaling, or cutting into prey.
Beyond the sixth tooth, however, the shape shifts. Teeth become more blade-like, better adapted for tearing and shearing flesh. This transition marks a functional division within the jaw where different teeth play different roles during feeding, much like how we as humans have incisors at the front and molars at the back of our mouths.
Even more striking were the changes that occur as sharks grow. At around 3m in body length, white sharks undergo a major dental transformation. Juvenile teeth are slimmer and often feature small side projections at the base of the tooth, called cusplets, which help to grip small slippery prey such as fish and squid.
As sharks approach 3m, these cusplets disappear and the teeth become broader, thicker, and serrated.
In many ways, this shift mirrors an ecological turning point. Young sharks rely on fish and small prey that require precision and an ability to grasp the smaller bodies. Larger sharks increasingly target marine mammals: big, fast-moving animals that demand cutting power rather than grip.
Once great whites reach this size, they develop an entirely new style of tooth capable of slicing through dense flesh and even bone.
Some teeth stand out even more. The first two teeth on either side of the jaw, the four central teeth, are significantly thicker at the base. These appear to be the primary “impact” teeth, taking the force of the initial bite.
Meanwhile, the third and fourth upper teeth are slightly shorter and angled, suggesting a specialised role in holding onto struggling prey. Their size and position may also be influenced by the underlying skull structure and the placement of key sensory tissues involved in smelling.
We also found consistent differences between the upper and lower jaws. Lower teeth are shaped for grabbing and holding prey, while upper teeth are designed for slicing and dismembering – a coordinated system that turns the white shark’s bite into a highly efficient feeding tool.
Scientists measured teeth from nearly 100 white sharks. Emily Hunt
A lifestory in teeth
Together, these findings tell a compelling story.
The teeth of white sharks are not static weapons but living records of a shark’s changing lifestyle. Continuous replacement compensates for teeth lost and damaged, but at least equally important, enables design updates that track diet changes through development.
This research helps us better understand how white sharks succeed as apex predators and how their feeding system is finely tuned across their lifetime.
It also highlights the importance of studying animals as dynamic organisms, shaped by both biology and behaviour. In the end, a white shark’s teeth don’t just reveal how it feeds – they reveal who it is, at every stage of its life.
This research has received in kind support for collection of specimens from the New South Wales Department of Primary Industries and Regional Development through the Shark Management Program. David Raubenheimer has no other relevant relationships or funding to declare.
Ziggy Marzinelli is an Associate Professor at The University of Sydney and receives funding from the Australian Research Council, the Ian Potter Foundation and the NSW Environmental Trust.
Emily Hunt does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.
Source: The Conversation – Global Perspectives – By David Blair, Emeritus Professor, ARC Centre of Excellence for Gravitational Wave Discovery, OzGrav, The University of Western Australia
Last year, astronomers were fascinated by a runaway asteroid passing through our Solar System from somewhere far beyond. It was moving at around 68 kilometres per second, just over double Earth’s speed around the Sun.
Imagine if it had been something much bigger and faster: a black hole travelling at more like 3,000km per second. We wouldn’t see it coming until its intense gravitational forces started knocking around the orbits of the outer planets.
This may sound a bit ridiculous – but in the past year several lines of evidence have come together to show such a visitor is not impossible. Astronomers have seen clear signs of runaway supermassive black holes tearing through other galaxies, and have uncovered evidence that smaller, undetectable runaways are probably out there too.
Runaway black holes: the theory
The story begins in the 1960s, when New Zealand mathematician Roy Kerr found a solution of Einstein’s general relativity equations that described spinning black holes. This led to two crucial discoveries about black holes.
First, the “no-hair theorem”, which tells us black holes can be distinguished only by three properties: their mass, their spin and their electric charge.
For the second we need to think about Einstein’s famous formula E = mc ² which says that energy has mass. In the case of a black hole, Kerr’s solution tells us that as much as 29% of a black hole’s mass can be in the form of rotational energy.
English physicist Roger Penrose deduced 50 years ago that this rotational energy of black holes can be released. A spinning black hole is like a battery capable of releasing vast amounts of spin energy.
A black hole can contain about 100 times more extractable energy than a star of the same mass. If a pair of black holes coalesce into one, much of that vast energy can be released in a few seconds.
It took two decades of painstaking supercomputer calculations to understand what happens when two spinning black holes collide and coalesce, creating gravitational waves. Depending on how the black holes are spinning, the gravitational wave energy can be released much more strongly in one direction than others – which sends the black holes shooting like a rocket in the opposite direction.
If the spins of the two colliding black holes are aligned the right way, the final black hole can be rocket-powered to speeds of thousands of kilometres per second.
Learning from real black holes
All that was theory, until the LIGO and Virgo gravitational wave observatories began detecting the whoops and chirps of gravitational waves given off by pairs of colliding black holes in 2015.
One of the most exciting discoveries was of black hole “ringdowns”: a tuning fork-like ringing of newly formed black holes that tells us about their spin. The faster they spin, the longer they ring.
Better and better observations of coalescing black holes revealed that some pairs of black holes had randomly oriented spin axes, and that many of them had very large spin energy.
All this suggested runaway black holes were a real possibility. Moving at 1% of light speed, their trajectories through space would not follow the curved orbits of stars in galaxies, but rather would be almost straight.
Runaway black holes spotted in the wild
This brings us to the final step in our sequence: the actual discovery of runaway black holes.
It is difficult to search for relatively small runaway black holes. But a runaway black hole of a million or billion solar masses will create huge disruptions to the stars and gas around it as it travels through a galaxy.
They are predicted to leave contrails of stars in their wake, forming from interstellar gas in the same way contrails of cloud form in the wake of a jet plane. Stars form from collapsing gas and dust attracted to the passing black hole. It’s a process that would last for tens of millions of years as the runaway black hole crosses a galaxy.
In 2025, several papers showed images of surprisingly straight streaks of stars within galaxies such as the image below. These seem to be convincing evidence for runaway black holes.
One paper, led by Yale astronomer Pieter van Dokkum, describes a very distant galaxy imaged by the James Webb telescope with a surprisingly bright contrail 200,000 light years long. The contrail showed the pressure effects expected from the gravitational compression of gas as a black hole passes: in this case it suggests a black hole with a mass 10 million times the Sun’s, travelling at almost 1,000km/s.
Another describes a long straight contrail cutting across a galaxy called NGC3627. This one is likely caused by a black hole of about 2 million times the mass of the Sun, travelling at 300km/s. Its contrail is about 25,000 light years long.
If these extremely massive runaways exist, so too should their smaller cousins because gravitational wave observations suggest that some of them come together with the opposing spins needed to create powerful kicks. The speeds are easily fast enough for them to travel between galaxies.
So runaway black holes tearing through and between galaxies are a new ingredient of our remarkable universe. It’s not impossible that one could turn up in our Solar System, with potentially catastrophic results.
We should not lose sleep over this discovery. The odds are minuscule. It is just another way that the story of our universe has become a little bit richer and a bit more exciting than it was before.
David Blair receives funding from the Australian Research Council. He is a member of the ARC Centre of Excellence for Gravitational Wave Discovery and is director of the Einstein-First education project that is developing a modern physics curriculum for primary and middle school science education.
Five years ago, on February 1 2021, Myanmar’s top generals decapitated the elected government. Democratic leaders were arrested, pushed underground or forced into exile.
Since then, the economy has spluttered and foreign investors have headed for the exit. The only growth industries – mostly scam centres, drugs and other criminal activities – enrich those already well-fed.
The military junta has kept its stranglehold via draconian curbs on civil and political liberties. It has bolstered its fighting forces through ruthless conscription, including of child soldiers. They now face rebellions in almost every corner of the ethnically diverse country.
It helps that the military brass can still depend on international support from Russia. China, meanwhile, is playing a careful game to ensure its interests – including prized access to the Indian Ocean for oil and gas – are secured.
And US President Donald Trump’s second term in office has introduced newly unpredictable and detrimental elements to great power politics.
The US government last year cited “notable progress in governance and stability [and] plans for free and fair elections” as justification for removing the Temporary Protected Status designation for immigrants from Myanmar. Although a federal judge blocked this decision a few days ago, this may eventually force previously protected Myanmar citizens to return home.
However, far from being free and fair, the month-long elections that just concluded in Myanmar have been devoid of meaningful democratic practice.
They will entrench the junta and provide little more than a patina of legitimacy that anti-democratic major powers will use to further normalise relations with Myanmar’s military leaders.
Myanmar’s deeply flawed election
The multi-stage elections were being held in only a fraction of the country currently under the military’s authority. Elections were not held in opposition-held territory, so many otherwise eligible voters were disenfranchised.
As such, there is no serious opposition to the military’s proxy, the Union Solidarity and Development Party (USDP). Civil and political space is also heavily restricted, with criticism of the election itself being a criminal offence.
The main opposition would be the National League for Democracy (NLD) party, which has won by a landslide in every national election it has participated in since 1990. But it has been banned, along with dozens of other opposition political parties. Its senior leaders, including Aung San Suu Kyi, have been imprisoned.
Despite recent military gains by the junta, supported by Russian military technology and Chinese government pressure, the lines of control may be starting to solidify into an eventual Balkanisation, or break up, of Myanmar into hostile statelets.
The prospects for a future federalised democratic Myanmar seem increasingly remote.
Since the coup there are many areas now under full opposition control. Take, for instance, a recent declaration of independence by a breakaway ethnic Karen armed group. While they represent only one part of the Karen community in eastern Myanmar, this could well precipitate a flood of similar announcements by other ethnic minorities.
Other groups might declare themselves autonomous and seek backing from governments and commercial and security interests in neighbouring countries such as China, Thailand, India and Bangladesh.
Most neighbouring countries will be uneasy about any further fracturing of Myanmar’s territorial integrity. Some, however, see potential benefits. China, for example, supports some ethnic armed groups to protect its strategic economic assets and maintain stability and influence along its borders.
Will international rulings have any impact?
While the conflict continues at home, Myanmar’s military leadership is defending itself at the International Court of Justice (ICJ) in The Hague. It faces claims it committed genocide against the Muslim Rohingya ethnic minority, particularly during the massacres of 2017.
Given the disdain for international law shown by Russia, China and the Trump administration in the US, any finding against the junta will have limited practical impact anyway.
What next?
Meanwhile, some countries in the the ASEAN bloc appear to be softening their opposition to the junta.
Recently, the Philippines foreign secretary met with Myanmar’s senior military leadership in the country’s first month chairing the bloc. This highlights the conundrum faced by regional leaders.
In the years immediately after the coup, ASEAN sought to keep Myanmar’s junta at arm’s length. But a number of key ASEAN players, particularly the more authoritarian regimes in Southeast Asia, would prefer to find a way to normalise engagement with the generals.
From that perspective, the flawed elections are a chance to embrace superficial democratisation and renewal.
This leaves the Myanmar people – millions of whom have fought hard against the coup and its negative consequences – with invidious choices about how to best pursue their independence and freedom.
There is little positive economic news on the horizon. The IMF projects inflation in Myanmar will stay above 30% in 2026 with a real GDP fall of 2.7%. This would compound an almost 20% contraction since the coup. The currency is worth around one quarter of what it was five years ago at the time of the coup.
In practice, this means many Myanmar families have gone backwards dramatically. An untold number are now entangled in illicit and often highly exploitative businesses.
The military’s proxy, the Union Solidarity and Development Party (USDP), will undoubtedly form government after the elections. But unlike the USDP-led government that formed after the similarly flawed 2010 election, this new administration is unlikely to pursue political and economic liberalisation sufficient to entice opposition forces to play along.
The people of Myanmar have now been betrayed and brutalised by the military far too often to believe their easy promises.
As a pro vice-chancellor at the University of Tasmania, Nicholas Farrelly engages with a wide range of organisations and stakeholders on educational, cultural and political issues, including at the ASEAN-Australia interface. He has previously received funding from the Australian government for Southeast Asia-related projects and from the Australian Research Council. Nicholas is on the advisory board of the ASEAN-Australia Centre, which is an Australian government body established in 2024, and also Deputy Chair of the board of NAATI, Australia’s government-owned accreditation authority for translators and interpreters. He writes in his personal capacity.
Adam Simpson does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.
Cuando los ingenieros diseñamos materiales para una determinada aplicación, lo hacemos de acuerdo a normas que nos indican qué propiedades deben reunir esos materiales para soportar sus condiciones más extremas de uso.
Si consideramos un raíl de ferrocarril, puede estar expuesto a fenómenos de corrosión, desgaste y, sobre todo, tensiones de tipo dinámico, que pueden provocar daños por fatiga. Combinar todas estas propiedades no es sencillo, por lo que al diseñar y fabricar el acero para raíles es esencial buscar un equilibrio y poner toda la atención en el daño que podría provocar un fallo motivado por cada uno de estos requerimientos.
La corrosión y el desgaste pueden generar defectos perfectamente detectables en inspecciones que no tienen por qué ser muy próximas entre sí, ya que el daño sobre el raíl nunca provocaría una rotura catastrófica en un periodo breve de tiempo (semanas o meses).
Otra cosa son las tensiones de tipo dinámico. Si un material supera su límite de fatiga –el número de ciclos de tensión que es capaz de soportar sin que se inicie una grieta–, esta aparecerá y empezará a crecer, inicialmente despacio, hasta alcanzar un tamaño crítico. Una vez se alcanza ese tamaño crítico, la grieta crece a tal velocidad que puede producir un fallo catastrófico en minutos, o incluso segundos.
El acero es el material más fiable de todos
Que un accidente ferroviario como el que ha tenido lugar recientemente en Adamuz se deba a una “mala calidad” del acero es poco probable, por varias razones. Para empezar, el acero es, sin duda, de entre todos los materiales de construcción, el más fiable: de cada cien probetas ensayadas, cien tienen resultados dentro de un estrechísimo margen de error.
En el caso de los aceros para raíles, hablamos de aceros de composiciones muy ajustadas para que cumplan con las propiedades mecánicas requeridas y que, además, permita que se puedan soldar.
Los ingenieros, que avalan con su firma los proyectos, calculan con márgenes de seguridad muy amplios y estándares de calidad que garantizan que los materiales nunca lleguen a superar sus límites de fatiga. Y esos márgenes vienen establecidos por normas internacionales.
Los fabricantes de los aceros implicados en el accidente (uno más antiguo y otro muy reciente) han producido miles de kilómetros de raíles, de acuerdo con normas muy estrictas y bajo criterios de garantía de calidad extremos. Hablamos de raíles que no han tenido ningún problema, fabricados con acero ajustado a norma, soldable y calculado para soportar la carga estática de un tren de varios cientos de toneladas y que, circulando a 250 kilómetros por hora, produce unas tensiones dinámicas muy por debajo de su límite de fatiga.
Si el acero está bien fabricado, y las certificaciones de calidad así lo aseguran, es muy improbable que ese acero se rompa en “condiciones de servicio”.
Soldaduras en el punto de mira
¿Y qué se debe esperar de la soldadura? Los raíles de ferrocarril se sueldan mediante una tecnología, llamada aluminotermia, que asegura la continuidad metálica con un acero de composición muy parecida a los de los raíles que tiene la futura soldadura a cada lado.
Parece que, en el caso concreto de las vías donde se produjo el accidente de Adamuz, había aceros de distinta composición. Los raíles de ambos lados están hechos con aceros de alta soldabilidad, por lo que es seguro que en la llamada “zona afectada por el calor” no se han producido fragilizaciones. De ser así, hubieran dado lugar a un accidente mucho antes.
Una soldadura “puede dar problemas” si se ejecuta de forma inapropiada, pero aquí la calidad se asegura de dos maneras. En primer lugar, dejando en manos de soldadores acreditados su ejecución. Y en segundo lugar, inspeccionando una por una, por inspección visual y por métodos que permiten ver la soldadura “por dentro”, todas las soldaduras realizadas. Por tanto, cuando se entrega una ejecución, se garantiza que todas las soldaduras se han hecho correctamente.
Cómo ha ocurrido lo imposible
A pesar de todo, en la tragedia de Alcamuz se baraja la opción de que una soldadura haya fallado y un trozo de raíl se haya fracturado, de forma catastrófica.
¿Cómo ha podido ocurrir, si era imposible que ocurriera?
Si la continuidad metálica desaparece (porque falla la soldadura) y los dos tramos de raíl quedan separados, cada vez que una rueda pase por encima de esos raíles estará trasladando una tensión en las proximidades de los extremos, muy superior a la tensión de diseño. Esto provocará que, en algún momento, se supere el límite de fatiga y se genere una grieta en el raíl. Esa grieta empezará a crecer y, cuando supere un determinado tamaño crítico, provocará una rotura catastrófica.
¿Y qué le pudo pasar a la soldadura?. Pues de momento todo indica que o bien hubo un mal diseño del material de la soldadura (en este momento, se está hablando de una posible elección inapropiada por culpa de una redacción equivocada del pliego de condiciones); o bien se produjo un defecto inicial en la ejecución de la soldadura tan pequeño que no fue detectado en el análisis posterior a su ejecución. Por supuesto pudieron pasar otras cosas, pero a priori no podemos presuponer malas practicas sin un peritaje adecuado.
Prevenir mejor que curar
Cuando somos jóvenes, es difícil que fallen algunos sistemas y no precisamos de revisiones periódicas; vamos al médico cuando nos duele algo. Y el médico, entonces, utiliza diversos medios para hacer un diagnóstico y arreglar el problema. Cuando alcanzamos cierta edad, no podemos esperar a que los problemas den la cara, debemos hacernos revisiones cada vez más frecuentes para evitar que los problemas generen un fallo catastrófico.
Lo de Alcamuz posiblemente no hubiera pasado si se hubiera atendido a los síntomas –tanto usuarios como algunos trabajadores de los trenes llevaban meses reportando vibraciones fuera de lo normal– y se hubieran hecho las revisiones pertinentes.
Todavía ignoramos lo que realmente pasó: habrá que esperar a la evaluación definitiva de los peritos. Para tranquilidad de todos, los ingenieros metalúrgicos tenemos medios, herramientas y conocimientos suficientes para escudriñar lo ocurrido. Exactamente del mismo modo que un médico forense puede averiguar con precisión la causa de un fallecimiento.
No tengo la menor duda de que pronto se sabrá, con todo detalle, qué generó el fallo y qué repercusiones tuvo en el resto de la infraestructura. Y ese informe también podrá aclarar si se pudo prevenir.
José Manuel Torralba no recibe salario, ni ejerce labores de consultoría, ni posee acciones, ni recibe financiación de ninguna compañía u organización que pueda obtener beneficio de este artículo, y ha declarado carecer de vínculos relevantes más allá del cargo académico citado.
Cada vez que se habla de infraestructuras, transición energética o reindustrialización, el acero vuelve al centro del debate. No es sorprendente: se trata del material estructural más utilizado del planeta.
El acero está ahí cuando cruzamos un puente, cuando entramos en un edificio, cuando subimos a un tren o encendemos la luz. Buena parte del entorno construido que hace posible nuestra vida cotidiana depende directa o indirectamente de este material.
¿Por qué es el material más utilizado? Porque combina bajo coste y disponibilidad, eso sin duda. Pero también porque reúne propiedades difíciles de encontrar juntas en otros materiales: alta resistencia mecánica, capacidad de deformarse sin romperse, durabilidad, facilidad de fabricación, reciclabilidad y una enorme versatilidad. Precisamente por eso es también uno de los materiales más estudiados y mejor conocidos por la ingeniería moderna.
Sin embargo, esa fiabilidad no es automática. El buen comportamiento del acero depende de cómo se fabrica, de su composición química y, de forma muy especial, de cómo se calienta y se enfría a lo largo de su vida. Es decir, de su historia térmica.
Entender cómo influyen el calor, el enfriamiento y el contenido de carbono es clave para explicar por qué el acero funciona tan bien… y por qué ciertos procesos industriales exigen un control tan estricto.
El acero “recuerda” el calor
Una idea fundamental, y a lo mejor poco intuitiva de la ciencia de materiales, es que el acero no tiene propiedades fijas e inmutables. Su dureza, su resistencia o su capacidad para absorber energía dependen no solo de qué acero es, sino también de su historia térmica. Es decir, de cómo ha sido calentado y enfriado durante su fabricación y transformación.
Podemos decir que el acero, en cierto modo, “recuerda” el calor. Aunque una pieza no muestre ningún cambio visible, a nivel interno pueden producirse reorganizaciones que alteran su comportamiento mecánico. Por eso, dos componentes fabricados con el mismo acero pueden responder de forma distinta ante una misma carga si han seguido trayectorias térmicas diferentes. Esta “memoria térmica” explica tanto la enorme versatilidad del acero como la necesidad de controlar cuidadosamente los procesos térmicos.
Un tratamiento térmico consiste, de forma simplificada, en calentar el acero hasta una determinada temperatura, mantenerlo durante un tiempo controlado y enfriarlo después a una velocidad concreta. El objetivo no es maximizar una propiedad aislada, sino encontrar el equilibrio adecuado entre resistencia y capacidad de deformarse sin romperse, del que depende la fiabilidad de muchas estructuras durante décadas de servicio.
Aquí aparece una idea clave: el tiempo es tan importante como la temperatura. Dos aceros pueden alcanzar la misma temperatura máxima y, sin embargo, comportarse de forma muy distinta si el enfriamiento ha sido más rápido o más lento. Este principio explica por qué un mismo acero puede ofrecer prestaciones muy diferentes dependiendo de cómo se haya tratado térmicamente.
Esta idea resulta intuitiva incluso fuera del ámbito técnico. Programas televisivos como “Forjado a fuego” muestran cómo una misma pieza de acero puede comportarse de forma radicalmente distinta según cómo se enfríe tras salir del fuego. Aunque en televisión el proceso parezca artesanal, el principio es exactamente el mismo que rige los tratamientos térmicos industriales: entender cómo la temperatura, el tiempo y la composición interactúan para determinar el comportamiento final del material.
El papel de la composición: pequeñas cantidades, grandes efectos
El acero es, esencialmente, una aleación de hierro y carbono. Aunque el carbono esté presente en pequeñas cantidades, su influencia es enorme: variaciones muy pequeñas pueden cambiar de forma significativa cómo el acero responde al calentamiento y al enfriamiento.
El carbono determina en gran medida la respuesta del acero a los tratamientos térmicos, pero no actúa solo. Otros elementos de aleación, añadidos en cantidades controladas, permiten ajustar propiedades como la resistencia, la tenacidad o la durabilidad. Por eso, aceros con composiciones muy similares pueden comportarse de forma distinta si su composición o su historia térmica no son exactamente iguales.
Para entender esta relación entre composición y temperatura, ingenieros y científicos utilizan modelos conceptuales como el diagrama hierro–carbono, bien conocido —y sufrido— por generaciones de estudiantes de ingeniería. Aunque no describe piezas reales, actúa como un mapa que ayuda a comprender por qué pequeñas variaciones de composición y temperatura tienen un efecto tan grande en el comportamiento del acero.
Por qué las vías ferroviarias se fabrican con acero
Nada de esto significa que el acero utilizado en infraestructuras críticas sea un material impredecible. Todo lo contrario: en aplicaciones como las vías ferroviarias se emplean aceros al carbono específicamente diseñados para uso ferroviario, con composiciones cuidadosamente ajustadas para ofrecer un comportamiento mecánico estable, predecible y duradero.
Estos aceros se seleccionan precisamente por su fiabilidad frente a cargas repetidas, desgaste y largos periodos de servicio. Su composición y sus tratamientos térmicos no son fruto del azar, sino del conocimiento acumulado sobre cómo responde el acero cuando se controla correctamente el calor.
Cuando el calor deja de ser uniforme: soldadura y zona afectada por el calor
La mayor parte de los tratamientos térmicos industriales se realizan en condiciones muy controladas y uniformes. Sin embargo, no todos los procesos que implican calor permiten ese mismo grado de control. En algunos casos, el calor se aplica de forma intensa y localizada.
La soldadura es un buen ejemplo. Durante este proceso, una región muy concreta del acero alcanza temperaturas elevadas, mientras que el material circundante permanece relativamente frío. El enfriamiento posterior se produce de manera rápida y no homogénea, dando lugar a una zona cercana a la unión que ha experimentado un ciclo térmico distinto al del resto del componente: la zona afectada por el calor (ZAC).
Aunque visualmente no se distinga, la ZAC puede presentar propiedades diferentes porque su historia térmica ha cambiado. Por eso, la soldadura exige procedimientos tan estrictos: no porque el acero sea un material poco fiable, sino precisamente porque su comportamiento frente al calor es bien conocido y debe gestionarse con cuidado.
La soldadura del acero exige procedimientos estrictos. No porque el acero sea un material poco fiable, sino precisamente porque su comportamiento frente al calor es bien conocido y debe gestionarse con cuidado.
Entender el acero para confiar en él
Que el acero sea el material estructural más utilizado del mundo no es una coincidencia. Su éxito no se basa en que sea insensible o inmutable, sino en que su respuesta a la temperatura, al tiempo y a la composición es conocida, predecible y controlable. Esa sensibilidad al calor, lejos de ser una debilidad, es lo que permite adaptar el acero a aplicaciones muy distintas manteniendo altos niveles de fiabilidad.
Comprender cómo el acero cambia —aunque no lo veamos— es clave para valorar la ingeniería que hay detrás de las infraestructuras que utilizamos cada día. En un mundo que sigue construyéndose, moviéndose y transformándose sobre acero, entender el papel del calor y del carbono es una forma de entender por qué este material sigue siendo, y seguirá siendo, uno de los pilares fundamentales de nuestra sociedad.
Paula Alvaredo Olmos no recibe salario, ni ejerce labores de consultoría, ni posee acciones, ni recibe financiación de ninguna compañía u organización que pueda obtener beneficio de este artículo, y ha declarado carecer de vínculos relevantes más allá del cargo académico citado.
Source: The Conversation – USA – By Laura Tedesco, Professor of International and Comparative Politics, Saint Louis University – Madrid
A series of shootings by federal immigration agents, including two deaths in Minneapolis, have galvanized intense local and national protests against the Trump administration’s immigration enforcement operations. Federal immigration agents killed Renee Nicole Good, 37 – a mother of three – and Alex Pretti, a 37-year-old nurse, weeks apart in January 2026.
Historically in the U.S., police and other official state security forces have used face coverings almost exclusively during undercover operations to protect agent safety and the integrity of ongoing investigations, according to federal law enforcement sources.
The global human rights group Amnesty International has begun using the phrase “the Trump effect” to describe masking and other administration actions that it believes violate global human rights standards.
Several United Nations principles require that police action be guided at all times by legality, necessity, proportionality and nondiscrimination. Any use of force that does not comply with these principles violates international law.
Amnesty International’s policing guidance is based on these standards. It explains that police must attempt to use nonviolent means first, such as verbal commands, negotiation and warnings.
When force is necessary, officers must use “the least harmful means likely to be effective.” In such cases, proportionality requires that “the harm caused by the use of force may never outweigh the damage it seeks to prevent.”
As nonimmigrant local community members, neither victim would be the apparent target of immigration enforcement operations in Minneapolis.
Argentina’s dictatorship
In both its use of masks and its brazen disregard for proportionality, ICE evokes in me unsettling memories of all-powerful, authoritarian governments that exercise control over life and death.
Between 1976 and 1983, approximately 30,000 people were forcibly “disappeared,” meaning secretly kidnapped, never to be seen again. The vast majority were young men and women involved in labor unions, political organizations or student movements with left-wing ideologies, including Catholic priests and nuns who embraced liberation theology, a movement within the church that interprets the gospel of Jesus Christ through the experiences of poor people and the oppressed.
In April 1977, roughly a year after young Argentines first began vanishing, 14 women gathered in the Plaza de Mayo, a central square in Buenos Aires that faces the presidential palace. They were searching for their sons and daughters, who had been detained by the police or the military.
Some of these arrests had taken place at night, in the homes where these young victims lived with their families. In those cases, the women – who came to be known as the Madres de la Plaza de Mayo, or Mothers of the Plaza de Mayo – knew their children had been taken by security forces. In other cases, their children had simply failed to return home. Nothing was known of their whereabouts. They had disappeared.
Even those who had been detained at home had disappeared, too, as their location remained unknown.
Later, the nation would learn that many of the regime’s victims were tortured, then flown in airplanes over the nearby River Plate and dropped into the water on so-called “death flights.” All this information was compiled in a 1984 report written during the first democratic government after military rule and published under the name “Nunca Mas”: Never again.
The dictatorship had imposed a state of siege prohibiting all forms of assembly. To technically evade this restriction, the Mothers walked in circles around the plaza, avoiding the concentration of people in any single location, demanding truth and justice.
The regime reacted by systematically attempting to discredit the grieving women. To weaken their moral authority, state-controlled media labeled them as emotionally unstable “mad women.” The were called Las Locas de Plaza de Mayo instead of the Madres de Plaza de Mayo.
Officials accused the women of exaggerating or inventing kidnappings and sometimes mocked their ever-growing weekly marches. By attacking their credibility and dignity, the dictatorship sought to undermine public sympathy and maintain a climate of fear.
At first, this narrative worked. Early in the dictatorship, many Argentines viewed the Mothers with ambivalence, skepticism or even fear. Others, while privately sympathetic, avoided expressing support due to fear of repression and social consequences.
The government’s attacks were not only rhetorical. In 1977, three of the founding Mothers – Esther de Balestrino, Azucena Villaflor and Mary Ponce de Bianco – disappeared when a group of military personnel stormed the Church of the Holy Cross in Buenos Aires. Twelve other people were abducted. None have ever been found.
The Mothers received substantial support from abroad. International human rights organizations, foreign journalists and religious institutions all played a crucial role in legitimizing their claims and broadcasting their struggle to the world.
France, in particular, helped publicize the Mothers’ cause in Europe, which put diplomatic pressure on the Argentine regime. This international solidarity contributed significantly to breaking the dictatorship’s silence and exposing its crimes.
After democratic elections were held in October 1983, the Mothers continued their efforts to uncover the histories of their children and to find and bury their remains. Many also started working to locate their grandchildren who had been born in captivity and illegally adopted after their parents were disappeared.
Their dedication to recovering their loved ones exposed the full extent of the regime’s atrocities.
Argentines hold images of disappeared people in Buenos Aires during the trial of Argentina’s last dictator in 2010. Rolando Andrade Stracuzzi Source/AP
In 1983, President Raúl Alfonsín, who reestablished Argentine democracy, established the National Genetic Data Bank to identify kinship between the parents and children of the disappeared. Thousands of analyses were conducted on children suspected of being born in captivity and illegally adopted by military families.
More than 120 grandchildren have since been identified.
The Mothers and children of the disappeared have also played a fundamental role in convicting dozens of military officials for crimes against humanity. As direct witnesses to the long-term consequences of forced disappearance, they have repeatedly testified against military officials.
The Mothers’ activism, which continues today, has helped sustain public pressure in Argentina for accountability and to transform private trauma into collective political action.
The killings in Minneapolis inspired me to recount this story for a simple reason: The government can protect, condemn or kill. Argentine history shows that it matters how society reacts to state terrorism.
This story was produced in collaboration with Rewire News Group, a nonprofit news organization that covers reproductive health.
Parts of India, including the capital Delhi, were once again covered in thick smog recently as toxic pollution from industry and crop-burning engulfed the region. Even though India’s National Clean Air Programme has advanced clean air action, air pollution remains a reoccurring problem.
Reliably protecting public health will require tighter co-ordination across orders of governments and departments. Air pollution is shaped by different economic sectors, weather, geography and siloed institutions. Single-sector fixes alone, like pausing construction or banning older vehicles, are unlikely to deliver system-wide change.
That’s why our team conducted a study to map air quality governance in India as an interconnected system, linking the parts that determine what gets measured, what gets enforced, what gets funded and what persists beyond city boundaries.
In addition to the authors of this article, our research team included Christoph Becker and Teresa Kramarz from the University of Toronto, Om Damani and Anshul Agarwal at the Indian Institute of Technology Bombay and Ronak Sutaria from the environmental consultant Respirer Living Sciences.
Our goal was to identify leverage points in current governance where shifts could deliver the greatest pollution-related health benefits.
If we want clean air to be a public service, we need pathways for communities to participate meaningfully. Our research argues for steady funding and training to build community monitoring literacy so accountability and action persist beyond political cycles.
Developing hyper-local monitoring
One hopeful example comes from the city of Bengaluru in the south of the country.
In this case, community groups installed monitors near schools and hospitals, using the data to spotlight the problem and seek court-mandated enforcement — underscoring the need for clear pathways to use community-generated data in enforcement.
The efforts by the communities aren’t meant to be a substitute for government enforcement. The point is to empower communities and give them a real choice in a system where they have very little voice.
The government monitors air pollution to track pollution levels over time and across locations, and to evaluate whether policies and enforcement are improving air quality.
Although India does need to scale monitoring capacities and make them equitable, we already have enough data streams from satellite observations, reference-grade monitors and low-cost sensors.
The real governance gap is in how these data streams can be used for action: standards for calibration in local conditions, quality assurance and control, and protocols for integrating evidence into enforcement and planning.
We recommend certification and quality assurance and control protocols for hyper-local monitoring so agencies can rely on the data for decisions and enforcement.
This data played a critical role in identifying street-level pollution hotspots, evaluating traffic interventions and assessing the impacts of policies such as the city’s Ultra Low Emission Zone. Indian governments can learn from this example.
When data is standardized for defined-decision contexts, it enables decision-making.
Governing the airshed
Air pollution does not respect regional or city boundaries. Yet, the National Clean Air Programme often assigns actions to cities, even when cities cannot control a large share of the pollution they face. For example, even when Delhi tightens local restrictions of cars or construction, at least a dozen coal-fired power plants near the city continue to operate without key pollution filters.
This is why we need governance at the airshed scale. An airshed is a region where local weather and geography, such as mountains, influence how air and pollutants move.
Governments must look at how air pollution spreads in an area, then develop rules for co-ordinating across jurisdictions. That means setting out clear roles for different departments, establishing shared data standards and creating dispute-resolution mechanisms so co-ordinated efforts can address the issue effectively.
Right now, the Clean Air Programme is centred on cutting the level of particulate matter in the air by roughly 20-30 per cent. A more actionable approach is figuring out which sectors are driving the airshed pollution — namely transport, construction, industry, power, waste and household fuels — and what sector-specific targets and timelines would actually lead to healthier air.
India’s Commission for Air Quality Management (CAQM), for example, was created specifically to put airshed-level management into practice across state and jurisdictional boundaries under the National Clean Air Programme.
The hardest part is assigning enforceable responsibilities across ministries (like power, transport, agriculture, industry, urban development) at the national, state and local levels, as well as across states.
For instance, agencies like CAQM (and NCAP more broadly) can take airshed-wide pollution inventories (estimates of how much pollution comes from different sources and sectors across an airshed) and translate them into short-term, sector-by-sector targets for each ministry, with deadlines and clear accountability.
Rewrite the objective to protect health
In our paper, we recommend expanding regulatory goals to include public health protection, in addition to meeting particulate matter targets. Putting health at the centre can shape governmental priorities, pushing agencies to focus first on the sources people are most exposed to.
As Ronak Sutaria, the founder and CEO of Respirer Living Sciences and a co-author of our study, told us:
“Air pollution isn’t an environmental statistic; it’s a public-health emergency that shows up in asthma, heart disease and hospital admissions. When we map air quality at the neighbourhood level and link it to health outcomes, clean air can move from a promise to a right — because communities can see what they’re breathing and what it means for their health, and that changes what polluters can get away with.”
A health-first objective also pushes governance toward equity, because exposure burdens are unevenly distributed across different segments of the population.
Airsheds differ, and so must actions to clean up the air. The value of systems thinking is that it offers a common way to understand what is limiting progress locally and design governance that fits local realities.
The authors do not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and have disclosed no relevant affiliations beyond their academic appointment.
This winter’s Olympic games will not be a normal international sporting event. A cloud of geopolitical tension looms over the Milan Cortina Winter Olympics, as well as the upcoming FIFA Men’s World Cup.
International sports events provide widespread media coverage and brand exposure. That spotlight is particularly attractive for authoritarian and repressive regimes seeking legitimacy on the world stage.
Access to a western audience provides these states with the opportunity to “sportswash” their legitimate authority through a carefully curated image.
Repressive regimes have increasingly pursued this strategy. Research shows that the share of international sporting events hosted by autocracies fell from 36 per cent in 1945-88 to 15 per cent in 1989-2012, but has rebounded to 37 per cent since 2012.
Sportswashing can also work to establish broader global acceptance of repressive regimes, particularly when western institutions accept their wealth and acquiesce to their goals.
There is often a symbiotic relationship between repressive regimes and international sporting organizations. However, the Milan–Cortina Games are unlikely to serve up the sportswashing narratives we have seen recently. Instead, the political stories of the 2026 Winter Olympics are likely to be more explicitly nationalist.
Sport is a powerful vehicle for national rhetoric. It can reinforce a person’s social identity or how they see themselves in relation to others by encouraging people to see themselves as a member of a team or country, and celebrating victory as a collective success or interpreting defeat as a symbolic loss.
Whether it’s tension between the European Union and the U.S. or between Canada and the U.S., there are many story lines that can serve as galvanizing moments for nationalist rhetoric.
The men’s ice hockey tournament at the 1980 winter Olympics in Salt Lake City, Utah, served as a pivotal moment in the Cold War. When the underdog U.S. beat the favoured Soviet Union Red Army team, it was deemed the “Miracle on Ice.”
Given Trump’s threats against Greenland, a Danish territory, the Olympics matchup between the two teams could serve as Denmark’s own “miracle on ice” moment.
A medal table ripe for political spin
Beyond ice hockey, this is shaping up to be a Winter Olympics the U.S. is likely to perform quite well in. Traditional winter powerhouses Norway and Russia are both facing scandals or exclusion.
A successful Winter Olympics could therefore provide political capital at a sensitive moment. Amid his attack on Venezuela and stated goal of acquiring Greenland, major soccer countries and EU powerbrokers — including France and Germany — have started to tentatively reconsider their participation in the 2026 Men’s World Cup, hosted in large part by the U.S.
But first, the 2026 Winter Olympics will serve up a menu of matchups that stand to serve the nationalist goals of Trump, Carney and leaders across the European Union.
Noah Eliot Vanderhoeven does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.
El discurso contemporáneo sobre las mujeres incorpora de forma creciente la idea de elección individual. La maternidad aparece, al menos en términos normativos, como una posibilidad entre otras. Sin embargo, esta aparente apertura convive con una realidad persistente: la maternidad continúa ocupando un lugar central en la construcción social de la identidad femenina.
Cuando una mujer supera los 35 años sin haber sido madre –ya sea por decisión propia, por dificultades reproductivas o por circunstancias vitales– su trayectoria sigue siendo objeto de juicio.
La maternidad como norma cultural
A pesar de los cambios sociales, la maternidad se sigue asociando a la idea de una vida femenina “plena” o “realizada”. El mandato de la maternidad adopta formas más sutiles, pero no desaparece. No se presenta únicamente como una opción vital, sino como una expectativa implícita que estructura las representaciones sobre lo que significa ser mujer.
Dicha expectativa se intensifica a partir de cierta edad: a partir de los 35 años se activa el discurso del llamado “reloj biológico”. Más allá de su dimensión biológica, se trata de una construcción social que establece una temporalidad normativa para la maternidad y refuerza el control simbólico sobre el cuerpo y las decisiones reproductivas de las mujeres.
En este contexto, la ausencia de maternidad suele interpretarse como una responsabilidad individual y rodeada de la necesidad de justificar las decisiones personales de las mujeres. La maternidad deja así de situarse en el ámbito de la elección para convertirse en una norma cultural cuyo incumplimiento requiere demasiadas explicaciones.
Invisibilidad social y jerarquías simbólicas
La no maternidad también tiene implicaciones en el ámbito de las relaciones. En muchos entornos, el hecho de ser madre continúa funcionando como eje organizador de la vida adulta y genera dinámicas de pertenencia y exclusión que sitúa a las mujeres sin hijos en una posición periférica.
Persisten representaciones que asocian la no maternidad con la soledad, la falta de vínculos o una supuesta orientación individualista.
Estas ideas colocan a las mujeres sin hijos en un lugar secundario dentro de espacios de la vida adulta y se convierte en tema central de socialización. Conversaciones y actividades cotidianas giran en torno a la crianza, reforzando la idea de que esta experiencia constituye el núcleo de la vida femenina.
Esta jerarquización simbólica genera la invisibilidad de otras formas de relación, cuidado y compromiso y contribuyen a percibir la identidad de las mujeres en una sociedad marcada por profundos roles tradicionales.
Impacto emocional, legitimidad y estigma
A pesar de los avances normativos y culturales, los estigmas asociados a la no maternidad siguen presentes. La idea de la mujer “incompleta”, “egoísta” o “fracasada” continúa formando parte del imaginario colectivo, aunque se exprese de manera menos explícita que en décadas anteriores.
Las narrativas influyen tanto en la valoración social como en la forma en que las propias mujeres interpretan su experiencia vital, con efectos directos sobre la autoestima y el sentido de pertenencia.
Las consecuencias emocionales de este mandato social son relevantes. La presión constante por explicar la no maternidad puede generar sentimientos de culpa, inseguridad o insuficiencia, incluso cuando las decisiones tomadas responden a un proyecto de vida coherente.
Más allá de la maternidad
El análisis de estas dinámicas muestra que, pese a los avances discursivos, la maternidad sigue funcionando como una norma social que organiza la vida de las mujeres. No ser madre después de los 35 años se mantiene como una desviación respecto al modelo dominante.
Cuestionar esta lógica no implica restar valor a la maternidad, sino situarla claramente en el ámbito de la elección y no de la obligación. Reconocer la diversidad de trayectorias vitales resulta fundamental para avanzar hacia una sociedad en la que las mujeres no tengan que justificar continuamente sus decisiones ni su validez en función de un único modelo de vida.
María del Carmen Sánchez-Miranda no recibe salario, ni ejerce labores de consultoría, ni posee acciones, ni recibe financiación de ninguna compañía u organización que pueda obtener beneficio de este artículo, y ha declarado carecer de vínculos relevantes más allá del cargo académico citado.
