500 research outputs found
Bath-induced decay of Stark many-body localization
We investigate the relaxation dynamics of an interacting Stark-localized
system coupled to a dephasing bath, and compare its behavior to the
conventional disorder-induced many body localized system. Specifically, we
study the dynamics of population imbalance between even and odd sites, and the
growth of the von Neumann entropy. For a large potential gradient, the
imbalance is found to decay on a time scale that grows quadratically with the
Wannier-Stark tilt. For the non-interacting system, it shows an exponential
decay, which becomes a stretched exponential decay in the presence of finite
interactions. This is different from a system with disorder-induced
localization, where the imbalance exhibits a stretched exponential decay also
for vanishing interactions. As another clear qualitative difference, we do not
find a logarithmically slow growth of the von-Neumann entropy as it is found
for the disordered system. Our findings can immediately be tested
experimentally with ultracold atoms in optical lattices
Prethermal memory loss in interacting quantum systems coupled to thermal baths
We study the relaxation dynamics of an extended Fermi-Hubbard chain with a
strong Wannier-Stark potential tilt coupled to a bath. When the system is
subjected to dephasing noise, starting from a pure initial state the system's
total von Neumann entropy is found to grow monotonously. The scenario becomes
rather different when the system is coupled to a thermal bath of finite
temperature. Here, for sufficiently large field gradients and initial energies,
the entropy peaks in time and almost reaches its largest possible value
(corresponding to the maximally mixed state), long before the system relaxes to
thermal equilibrium. This entropy peak signals a prethermal memory loss and,
relative to the time where it occurs, the system is found to exhibit a simple
scaling behavior in space and time. By comparing the system's dynamics to that
of a simplified model, the underlying mechanism is found to be related to the
localization property of the Wannier-Stark system, which favors dissipative
coupling between eigenstates that are close in energy
Heat transport in an optical lattice via Markovian feedback control
Ultracold atoms offer a unique opportunity to study many-body physics in a
clean and well-controlled environment. However, the isolated nature of quantum
gases makes it difficult to study transport properties of the system, which are
among the key observables in condensed matter physics. In this work, we employ
Markovian feedback control to synthesize two effective thermal baths that
couple to the boundaries of a one-dimensional Bose-Hubbard chain. This allows
for the realization of a heat-current-carrying state. We investigate the
steady-state heat current, including its scaling with system size and its
response to disorder. In order to study large systems, we use semi-classical
Monte-Carlo simulation and kinetic theory. The numerical results from both
approaches show, as expected, that for non- and weakly interacting systems with
and without disorder one finds the same scaling of the heat current with
respect to the system size as it is found for systems coupled to thermal baths.
Finally, we propose and test a scheme for measuring the energy flow. Thus, we
provide a route for the quantum simulation of heat-current-carrying steady
states of matter in atomic quantum gases
Characterization of Hydrolytic Degradation of U-f Joints Through Apparent Diffusivity
The hydrolytic aging of an adhesive joint (wood-urea/formaldehyde resin) is characterized by measurements of the apparent diffusivity of two inert gases within the bond. This kind of measurement is of some interest, because it includes both chemical and geometrical changes in joint structure.Apparent diffusivities are determined in a diffusion cell after various degradation times in a cold water bath. Our results show that diffusivity increases with aging time with an asymptotic trend. Nevertheless, when the joint undergoes cyclic aging (immersion/drying), chemical degradation occurs mainly during the first cycle, while mechanical degradation observed during the drying steps also appears during the following cycles. The values of apparent diffusivity show that the solute transport is a real diffusional transport phenomenon and that resin joints are not porous
COPD and cardiovascular disease
COPD is one of the major public health problems in people aged 40 years or above. It is currently the 4th leading cause of death in the world and projected to be the 3rd leading cause of death by 2020. COPD and cardiac comorbidities are frequently associated. They share common risk factors, pathophysiological processes, signs and symptoms, and act synergistically as negative prognostic factors. Cardiac disease includes a broad spectrum of entities with distinct pathophysiology, treatment and prognosis. From an epidemiological point of view, patients with COPD are particularly vulnerable to cardiac disease. Indeed, mortality due to cardiac disease in patients with moderate COPD is higher than mortality related to respiratory failure. Guidelines reinforce that the control of comorbidities in COPD has a clear benefit over the potential risk associated with the majority of the drugs utilized. On the other hand, the true survival benefits of aggressive treatment of cardiac disease and COPD in patients with both conditions have still not been clarified. Given their relevance in terms of prevalence and prognosis, we will focus in this paper on the management of COPD patients with ischemic coronary disease, heart failure and dysrhythmia.Novartis Portugal
Novartisinfo:eu-repo/semantics/publishedVersio
Describing many-body localized systems in thermal environments
In this work we formulate an efficient method for the description of
many-body localized systems in weak contact with thermal environments at
temperature . For this purpose we exploit the representation of the system
in terms of quasi-local integrals of motion (-bits) to derive a quantum
master equation using Born-Markov approximations. We show how this equation can
be treated by using quantum-jump Monte-Carlo techniques as well as by deriving
approximate kinetic equations of motion. As an example, we consider the
one-dimensional Anderson model for spinless fermions including also
nearest-neighbor interactions, which we diagonalize approximately by employing
a recently proposed method valid in the limit of strong disorder and weak
interactions. Coupling the system to a global thermal bath, we study the
transport between two leads with different chemical potentials at both of its
ends. We find that the temperature-dependent current is captured by an
interaction-dependent version of Mott's law for variable range hopping, where
transport is enhanced/lowered depending on whether the interactions are
attractive or repulsive, respectively. We interpret these results in terms of
spatio-energetic correlations between the -bits
Indication of critical scaling in time during the relaxation of an open quantum system
Phase transitions correspond to the singular behavior of physical systems in
response to continuous control parameters like temperature or external fields.
Near continuous phase transitions, associated with the divergence of a
correlation length, universal power-law scaling behavior with critical
exponents independent of microscopic system details is found. Recently,
dynamical quantum phase transitions and universal scaling have been predicted
and also observed in the non-equilibrium dynamics of isolated quantum systems
after a quench, with time playing the role of the control parameter. However,
signatures of such critical phenomena in time in open systems, whose dynamics
is driven by the dissipative contact to an environment, were so far elusive.
Here, we present results indicating that critical scaling with respect to time
can also occur during the relaxation dynamics of an open quantum system
described by mixed states. We experimentally measure the relaxation dynamics of
the large atomic spin of individual Caesium atoms induced by the dissipative
coupling via spin-exchange processes to an ultracold Bose gas of Rubidium
atoms. For initial states far from equilibrium, the entropy of the spin state
is found to peak in time, transiently approaching its maximum possible value,
before eventually relaxing to its lower equilibrium value. Moreover, a
finite-size scaling analysis based on numerical simulations shows that it
corresponds to a critical point with respect to time of the dissipative system
in the limit of large system sizes. It is signalled by the divergence of a
characteristic length at a critical time, characterized by critical exponents
that are found to be independent of system details
CD8 T cell-mediated depletion of HBV surface-antigen-expressing, bilineal-differentiated liver carcinoma cells generates highly aggressive escape variants
The expression of viral antigens in chronic hepatitis B virus (HBV) infection drives continuous liver inflammation, one of the main risk factors to develop liver cancer. HBV developed immune-suppressive functions to escape from the host immune system, but their link to liver tumor development is not well understood. Here, we analyzed if and how HBV surface antigen (HBs) expression in combined hepatocellular-cholangiocarcinoma (cHCC/iCCA) cells influences their antigenicity for CD8 T cells. We randomly isolated liver tumor tissues from AlfpCre+-Trp53fl/fl/Alb-HBs+ tg mice and established primary carcinoma cell lines (pCCL) that showed a bilineal (CK7+/HNF4α+) cHCC/iCCA phenotype. These pCCL uniformly expressed HBs (HBshi), and low levels of MHC-I (MHC-Ilo), and were transiently convertible to a high antigenicity (MHC-Ihi) phenotype by IFN-γ treatment. HBshi/pCCL induced HBs/(Kb/S190–197)-specific CD8 T cells and developed slow-growing tumors in subcutaneously transplanted C57Bl/6J (B6) mice. Interestingly, pCCL-ex cells, established from HBshi/pCCL-induced and re-explanted tumors in B6 but not those in immune-deficient Rag1−/− mice showed major alterations, like an MHC-Ihi phenotype, a prominent growth-biased gene expression signature, a significantly decreased HBs expression (HBslo) and a switch to fast-growing tumors in re-transplanted B6 or PD-1−/− hosts with an unlocked PD-1/PD-L1 control system. CD8 T cell-mediated elimination of HBshi/pCCL, together with the attenuation of the negative restraints of HBs in the tumor cells, like ER-stress, reveals a novel mechanism to unleash highly aggressive HBslo/pCCL-ex immune-escape variants. Under certain conditions, HBs-specific CD8 T-cell responses thus potentiate tumor growth, an aspect that should be considered for therapeutic vaccination strategies against chronic HBV infection and liver tumors.</p
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