2,004 research outputs found
Precision tests of General Relativity with Matter Waves
We review the physics of atoms and clocks in weakly curved spacetime, and how
each may be used to test the Einstein Equivalence Principle (EEP) in the
context of the minimal Standard Model Extension (mSME). We find that
conventional clocks and matter-wave interferometers are sensitive to the same
kinds of EEP-violating physics. We show that the analogy between matter-waves
and clocks remains true for systems beyond the semiclassical limit. We
quantitatively compare the experimentally observable signals for EEP violation
in matter-wave experiments. We find that comparisons of Li and Li
are particularly sensitive to such anomalies. Tests involving unstable
isotopes, for which matter-wave interferometers are well suited, may further
improve the sensitivity of EEP tests.Comment: Conference Proceedings for talk given in January, 2011 at the Winter
Colloquium on the Physics of Quantum Electronics. Submitted to the Journal of
Modern Optic
SrCu_2(BO_3)_2 - a Two Dimensional Spin Liquid
We study an extended Shastry-Sutherland model for SrCu_2(BO_3)_2 and analyze
the low lying parts of the energy spectrum by means of a perturbative unitary
transformation based on flow equations. The derivation of the 1-magnon
dispersion (elementary triplets) is discussed. Additionally, we give a
quantitative description (symmetries and energies) of bound states made from
two elementary triplets. Our high order results allow to fix the model
parameters for SrCu_2(BO_3)_2 precisely: J_1=6.16(10)meV, x:=J_2/J_1=0.603(3),
J_\perp=1.3(2)meV. To our knowledge this is the first quantitative treatment of
bound states in a true 2d model.Comment: 4 pages, 3 figures, Proceeding paper of the HFM2000 conference in
Waterloo, Canada, Jun 200
HEAPCRAFT: Quantifying and Predicting Collaboration in Minecraft
We present HEAPCRAFT: an open-source suite of tools for monitoring and improving collaboration in Minecraft. At the core of our system is a data collection and analysis framework or recording gameplay. We collected over 3451 playerhours of game behavior from 908 different players, and performed a general study of online collaboration. To make our game analytics easily accessible, we developed interactive information visualization tools and an analysis framework for players, administrators, and researchers to explore graphs, maps and timelines of live server activity. As part of our research, we introduce the collaboration index, a metric which allows server administrators and researchers to quantify, predict, and improve collaboration on Minecraft servers. Our analysis reveals several possible predictors of collaboration which can be used to improve collaboration on Minecraft servers. HEAPCRAFT is designed to be general, and has the potential to be used for other shared online virtual worlds
HeapCraft Social Tools: Understanding and Improving Player Collaboration in Minecraft
We introduce a framework to infuence and analyze player collaboration in Minecraft. The framework consists of a telemetry system and several tools to influence player behavior and provide value to server administrators to increase adoption. The data collection includes almost every aspect of gameplay and can be used for analysis beyond player collaboration.1 We started collecting data from several Minecraft servers in March 2015. Most data will be made available to researchers upon request.2 We have also demonstrated the use of our framework to statistically analyze player behavior in Minecraft. More details can be found [1]
Conformal higher-order viscoelastic fluid mechanics
We present a generally covariant formulation of conformal higher-order
viscoelastic fluid mechanics with strain allowed to take arbitrarily large
values. We give a general prescription to determine the dynamics of a
relativistic viscoelastic fluid in a way consistent with the hypothesis of
local thermodynamic equilibrium and the second law of thermodynamics. We then
elaborately study the transient time scales at which the strain almost relaxes
and becomes proportional to the gradients of velocity. We particularly show
that a conformal second-order fluid with all possible parameters in the
constitutive equations can be obtained without breaking the hypothesis of local
thermodynamic equilibrium, if the conformal fluid is defined as the long time
limit of a conformal second-order viscoelastic system. We also discuss how
local thermodynamic equilibrium could be understood in the context of the
fluid/gravity correspondence.Comment: 26 pages; v2: minor corrections; v3: minor corrections, to appear in
JHE
Poorer outcome of elderly patients treated with extended-field radiotherapy compared with involved-field radiotherapy after chemotherapy for Hodgkin's lymphoma: an analysis from the German Hodgkin Study Group
Background: The optimal treatment of elderly patients with Hodgkin's lymphoma (HL) is still a matter of debate. Since many of these patients receive combined modality treatment, we evaluated the impact of different radiation field sizes, that is extended-field (EF) or involved-field (IF) technique when given after four cycles of chemotherapy. Patients and methods: In the multicenter HD8 study of the German Hodgkin Study Group, 1204 patients with early-stage unfavorable HL were randomized to receive four cycles of chemotherapy followed by either radiotherapy (RT) of 30 Gy EF + 10 Gy to bulky disease (arm A) or 30 Gy IF + 10 Gy to bulky disease (arm B). A total of 1064 patients were assessable for the analysis. Of these, 89 patients (8.4%) were 60 years or older. Results: Elderly patients had a poorer risk profile. Acute toxicity from RT was more pronounced in elderly patients receiving EF-RT compared with IF-RT [World Health Organization (WHO) grade 3/4: 26.5% versus 8.6%)]. Freedom from treatment failure (FFTF, 64% versus 87%) and overall survival (OS, 70% versus 94%) after 5 years was lower in elderly patients compared with younger patients. Importantly, elderly patients had poorer outcome when treated with EF-RT compared with IF-RT in terms of FFTF (58% versus 70%; P = 0.034) and OS (59% versus 81%; P = 0.008). Conclusion: Elderly patients with early-stage unfavorable HL generally have a poorer risk profile and outcome when compared with younger patients. Treatment with EF-RT instead of IF-RT after chemotherapy has a negative impact on survival of elderly patients and should be avoide
A Rydberg Quantum Simulator
Following Feynman and as elaborated on by Lloyd, a universal quantum
simulator (QS) is a controlled quantum device which reproduces the dynamics of
any other many particle quantum system with short range interactions. This
dynamics can refer to both coherent Hamiltonian and dissipative open system
evolution. We investigate how laser excited Rydberg atoms in large spacing
optical or magnetic lattices can provide an efficient implementation of a
universal QS for spin models involving (high order) n-body interactions. This
includes the simulation of Hamiltonians of exotic spin models involving
n-particle constraints such as the Kitaev toric code, color code, and lattice
gauge theories with spin liquid phases. In addition, it provides the
ingredients for dissipative preparation of entangled states based on
engineering n-particle reservoir couplings. The key basic building blocks of
our architecture are efficient and high-fidelity n-qubit entangling gates via
auxiliary Rydberg atoms, including a possible dissipative time step via optical
pumping. This allows to mimic the time evolution of the system by a sequence of
fast, parallel and high-fidelity n-particle coherent and dissipative Rydberg
gates.Comment: 8 pages, 4 figure
Orbital superfluidity in the -band of a bipartite optical square lattice
The successful emulation of the Hubbard model in optical lattices has
stimulated world wide efforts to extend their scope to also capture more
complex, incompletely understood scenarios of many-body physics. Unfortunately,
for bosons, Feynmans fundamental "no-node" theorem under very general
circumstances predicts a positive definite ground state wave function with
limited relevance for many-body systems of interest. A promising way around
Feynmans statement is to consider higher bands in optical lattices with more
than one dimension, where the orbital degree of freedom with its intrinsic
anisotropy due to multiple orbital orientations gives rise to a structural
diversity, highly relevant, for example, in the area of strongly correlated
electronic matter. In homogeneous two-dimensional optical lattices, lifetimes
of excited bands on the order of a hundred milliseconds are possible but the
tunneling dynamics appears not to support cross-dimensional coherence. Here we
report the first observation of a superfluid in the -band of a bipartite
optical square lattice with -orbits and -orbits arranged in a
chequerboard pattern. This permits us to establish full cross-dimensional
coherence with a life-time of several ten milliseconds. Depending on a small
adjustable anisotropy of the lattice, we can realize real-valued striped
superfluid order parameters with different orientations or a
complex-valued order parameter, which breaks time reversal
symmetry and resembles the -flux model proposed in the context of high
temperature superconductors. Our experiment opens up the realms of orbital
superfluids to investigations with optical lattice models.Comment: 5 pages, 5 figure
Bacterial porin disrupts mitochondrial membrane potential and sensitizes host cells to apoptosis
The bacterial PorB porin, an ATP-binding beta-barrel protein of pathogenic Neisseria gonorrhoeae, triggers host cell apoptosis by an unknown mechanism. PorB is targeted to and imported by host cell mitochondria, causing the breakdown of the mitochondrial membrane potential (delta psi m). Here, we show that PorB induces the condensation of the mitochondrial matrix and the loss of cristae structures, sensitizing cells to the induction of apoptosis via signaling pathways activated by BH3-only proteins. PorB is imported into mitochondria through the general translocase TOM but, unexpectedly, is not recognized by the SAM sorting machinery, usually required for the assembly of beta-barrel proteins in the mitochondrial outer membrane. PorB integrates into the mitochondrial inner membrane, leading to the breakdown of delta psi m. The PorB channel is regulated by nucleotides and an isogenic PorB mutant defective in ATP-binding failed to induce delta psi m loss and apoptosis, demonstrating that dissipation of delta psi m is a requirement for cell death caused by neisserial infection
Lethal pneumatosis coli in a 12-month-old child caused by acute intestinal gas gangrene after prolonged artificial nutrition: a case report
<p>Abstract</p> <p>Introduction</p> <p>Pneumatosis coli is a rare disease with heterogeneous symptoms which can be detected in the course of various acute and chronic intestinal diseases in children, such as necrotizing enterocolitis, intestinal obstruction and intestinal bacteriological infections.</p> <p>Case presentation</p> <p>We report the case of a 12-month-old boy who died of pneumatosis coli caused by an acute intestinal gas gangrene after prolonged artificial alimentation.</p> <p>Conclusion</p> <p>While intestinal gas gangrene is a highly uncommon cause of pneumatosis coli, it is important to consider it as a differential diagnosis, especially in patients receiving a prolonged artificial food supply. These patients may develop intestinal gas gangrene due to a dysfunctional intestinal barrier.</p
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