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Quantum mechanics describes the unitary time evolution of isolated systems. In reality, every quantum system interacts with its environment, leading to an irreversible loss of the phase relation. Path integral based methods provide a rigorous description of the process of decoherence. We provide an overview over recent numerical methods suited to describe the non-perturbative regime of system bath interaction. -- Quantenmechanik beschreibt die unitäre Zeitentwicklung isolierter Systeme. In der Realität interagiert jedes Quantensystem mit seiner Umwelt, was zu einem irreversiblen Verlust von Phasenbeziehungen führt. Pfadintegralbasierte Methoden erlauben eine rigorose Beschreibung dieser Dekohärenzprozesse.
This is the final version of the author's diploma thesis written at the Humboldt University of Berlin in 1995. The topic is the flow of granular material in narrow vertical pipes, driven by the gravity, that is described by Langevin equations. Neglecting the interactions, we can solve the resulting Fokker-Planck equation for the homogeneous case. The consideration of inelastic collisions leads to a Boltzmann equation. Assuming local equilibrium, the hydrodynamic equations lead to the extension of the Langevin equation formalism for the inhomogeneous case. For certain parameter ranges, our formalism can also be used to describe traffic flows. We applied stability analyses to the hydrodynamic equations and found critical densities for the occurrence of particle clustering. We used numerical simulations of the Langevin equations to verify our homogeneous solution as well as the critical densities.
Elsewhere, beyond-classical quantum hardware, plus classical computing fires back
The vulnerability, disclosed 12 months ago, affects multiple manufacturers
"We are reassigning most affected employees across existing opportunities and programs
Researchers found that a Chinese sodium-ion battery performs far better than expected, with production quality and design features comparable to Tesla’s batteries。 If engineers can improve cold-weather charging and energy density, sodium could become a cheaper and more abundant alternative to lithium for EVs and large-scale energy storage
A bold claim that the universe’s accelerating expansion was an illusion has been put to the test—and failed。 Researchers found that the study behind the controversy made key mistakes when analyzing supernova data。 After revisiting the evidence, astronomers concluded that cosmic acceleration remains as strong as ever
Localization is one of the fundamental issues in sensor networks. It is almost always assumed that it must be solved by assigning coordinates to the nodes. This article discusses positioning algorithms from a theoretical, practical and simulative point of view, and identifies difficulties and limitations. Ideas for more abstract means of location awareness are presented and the resulting possible improvements for applications are shown. Nodes with certain topological or environmental properties are clustered, and the neighborhood structure of the clusters is modeled as a graph. Eines der fundamentalen Probleme in Sensornetzwerken besteht darin, ein Bewusstsein fuer die Position eines Knotens im Netz zu entwickeln. Dabei wird fast immer davon ausgegangen, dass dies durch die Zuweisung von Koordinaten zu erfolgen hat. In diesem Artikel wird auf theoretischer, praktischer und simulativer Ebene ein kritischer Blick auf entsprechende Verfahren geworfen, und es werden Grenzen aufgezeigt. Es wird ein Ansatz vorgestellt, mit dem in der Zukunft eine abstrakte Form von Lokationsbewusstsein etabliert werden kann, und es wird gezeigt, wie Anwendungen dadurch verbessert werden koennen. Er basie
NASA says a long-running air leak aboard the ISS recently worsened, leading engineers to investigate new suspected crack locations and consider a riskier repair strategy。 Astronauts were temporarily moved into a safe haven as a precaution before the repair was postponed for further analysis
Oxford physicists have created an entirely new type of Schrödinger’s cat-like quantum state using components that are themselves highly quantum in nature。 The advance could open new possibilities for more resilient quantum computers and deeper insights into the strange rules that govern the quantum universe
Using the Keck Observatory, astronomers measured the spins of dozens of giant planets and brown dwarfs orbiting distant stars。 They found that giant planets can spin faster than much more massive brown dwarfs, challenging simple assumptions about mass and rotation。 The results suggest that magnetic fields and formation processes play a major role i
A distant galaxy nicknamed Shadow Blaster may have revealed a surprising source of cosmic neutrinos: extreme star formation instead of a supermassive black hole。 The discovery suggests that hidden, dust-filled starburst galaxies could account for a significant fraction of the Universe’s high-energy neutrinos
At least three coal plants have been repeatedly cited for violating environmental regulations
Taiwan's drone spending plans for defense could also boost business overseas
One previously unreported SpaceX investor has ties to Chinese military contractors
Scientists have uncovered a surprising connection between quantum gravity and an exotic quantum state of matter that could explain why the universe isn’t expanding wildly fast。 The study suggests that the very shape of space-time may protect the cosmological constant from disruptive quantum effects
NASA has selected the Artemis III crew for a high-stakes 2027 mission designed to test the future of lunar exploration。 Astronauts will launch aboard Orion and perform unprecedented docking operations with lunar landers being developed by both Blue Origin and SpaceX。 The mission will require a remarkable sequence of heavy-lift rocket launches and c
Researchers gave top AI models a classic attention test used in psychology and found a major flaw。 While the models could correctly name colors in short lists, their performance deteriorated sharply as the task became longer and more complex。 Some leading systems fell from over 90% accuracy to nearly complete failure
Researchers say these coral strongholds may help repopulate more degraded reefs
Researchers developed a Wordle-solving strategy that succeeds 99% of the time by focusing on information gain rather than likely answers。 The method uses Shannon entropy to identify guesses that reveal the most about the hidden word。 Each guess is designed to slash uncertainty and narrow the possibilities faster