2,848 research outputs found
Disorder-Induced Stabilization of the Pseudogap in Strongly Correlated Systems
The interplay of strong interaction and strong disorder, as contained in the
Anderson-Hubbard model, is addressed using two non-perturbative numerical
methods: the Lanczos algorithm in the grand canonical ensemble at zero
temperature and Quantum Monte Carlo. We find distinctive evidence for a
zero-energy anomaly which is robust upon variation of doping, disorder and
interaction strength. Its similarities to, and differences from, pseudogap
formation in other contexts, including perturbative treatments of interactions
and disorder, classical theories of localized charges, and in the clean Hubbard
model, are discussed.Comment: 4.2 pages, 4 figure
Magnetism and pairing of two-dimensional trapped fermions
The emergence of local phases in a trapped two-component Fermi gas in an
optical lattice is studied using quantum Monte Carlo simulations. We treat
temperatures that are comparable or lower than those presently achievable in
experiments and large enough systems that both magnetic and paired phases can
be detected by inspection of the behavior of suitable short-range correlations.
We use the latter to suggest the interaction strength and temperature range at
which experimental observation of incipient magnetism and d-wave pairing are
more likely and evaluate the relation between entropy and temperature in
two-dimensional confined fermionic systems.Comment: 4 pages + supplementary materia
Optimized Confinement of Fermions in Two Dimensions
One of the challenging features of studying model Hamiltonians with cold
atoms in optical lattices is the presence of spatial inhomogeneities induced by
the confining potential, which results in the coexistence of different phases.
This paper presents Quantum Monte Carlo results comparing meth- ods for
confining fermions in two dimensions, including conventional diagonal
confinement (DC), a recently proposed 'off-diagonal confinement' (ODC), as well
as a trap which produces uniform den- sity in the lattice. At constant entropy
and for currently accessible temperatures, we show that the current DC method
results in the strongest magnetic signature, primarily because of its judicious
use of entropy sinks at the lattice edge. For d-wave pairing, we show that a
constant density trap has the more robust signal and that ODC can implement a
constant density profile. This feature is important to any prospective search
for superconductivity in optical lattices
A Low-Cost Monitoring Platform and Visual Interface to Analyse Thermal Comfort in Smart Building Applications Using a Citizen–Scientist Strategy
Smart building issues are critical for current energy and comfort managing aspects in built environments. Nevertheless, the diffusion of smart monitoring solutions via user-friendly graphical interfaces is still an ongoing issue subject to the need to diffuse a smart building culture and a low-cost series of solutions. This paper proposes a new low-cost IoT sensor network, exploiting Raspberry Pi and Arduino platforms, for collecting real-time data and evaluating specific thermal comfort indicators (PMV and PPD). The overall architecture was accordingly designed, including the hardware setup, the back-end and the Android user interface. Eventually, three distinct prototyping platforms were deployed for initial testing of the general system, and we analysed the obtained results for different building typologies and seasonal periods, based on collected data and users’ preferences. This work is part of a large educational and citizen science activity
Whole-body heat stress and exercise stimulate the appearance of platelet microvesicles in plasma with limited influence of vascular shear stress
Intense, large muscle mass exercise increases circulating microvesicles, but our understanding of microvesicle dynamics and mechanisms inducing their release remains limited. However, increased vascular shear stress is generally thought to be involved. Here, we manipulated exercise-independent and exercise-dependent shear stress using systemic heat stress with localized single-leg cooling (low shear) followed by single-leg knee extensor exercise with the cooled or heated leg (Study 1, n = 8) and whole-body passive heat stress followed by cycling (Study 2, n = 8). We quantified femoral artery shear rates (SRs) and arterial and venous platelet microvesicles (PMV-CD41+) and endothelial microvesicles (EMV-CD62E+). In Study 1, mild passive heat stress while one leg remained cooled did not affect [microvesicle] (P ≥ 0.05). Single-leg knee extensor exercise increased active leg SRs by ~12-fold and increased arterial and venous [PMVs] by two- to threefold, even in the nonexercising contralateral leg (P < 0.05). In Study 2, moderate whole-body passive heat stress increased arterial [PMV] compared with baseline (mean±SE, from 19.9 ± 1.5 to 35.5 ± 5.4 PMV.μL-1.103, P < 0.05), and cycling with heat stress increased [PMV] further in the venous circulation (from 27.5 ± 2.2 at baseline to 57.5 ± 7.2 PMV.μL-1.103 during cycling with heat stress, P < 0.05), with a tendency for increased appearance of PMV across exercising limbs. Taken together, these findings demonstrate that whole-body heat stress may increase arterial [PMV], and intense exercise engaging either large or small muscle mass promote PMV formation locally and systemically, with no influence upon [EMV]. Local shear stress, however, does not appear to be the major stimulus modulating PMV formation in healthy humans
The response to dynamical modulation of the optical lattice for fermions in the Hubbard model
Fermionic atoms in a periodic optical lattice provide a realization of the
single-band Hubbard model. Using Quantum Monte Carlo simulations along with the
Maximum Entropy Method, we evaluate the effect of a time-dependent perturbative
modulation of the optical lattice amplitude on atomic correlations, revealed in
the fraction of doubly-occupied sites. Our treatment extends previous
approaches which neglected the time dependence of the on-site interaction, and
shows that this term changes the results in a quantitatively significant way.
The effect of modulation depends strongly on the filling-- the response of the
double occupation is significantly different in the half-filled Mott insulator
from the doped Fermi liquid region.Comment: 4 pages, 4 figure
Dehydration accelerates reductions in cerebral blood flow during prolonged exercise in the heat without compromising brain metabolism
Dehydration hastens the decline in cerebral blood flow (CBF) during incremental exercise, while the cerebral metabolic rate for oxygen (CMRO2) is preserved. It remains unknown whether CMRO2 is also maintained during prolonged exercise in the heat and whether an eventual decline in CBF is coupled to fatigue. Two studies were undertaken. In study 1, ten male cyclists cycled in the heat for ~2 h with (control) and without fluid replacement (dehydration) while internal (ICA) and external (ECA) carotid artery blood flow and core and blood temperature were obtained. Arterial and internal jugular venous blood samples were assessed with dehydration to evaluate the CMRO2. In study 2 (8 males), middle cerebral artery blood velocity (MCA Vmean) was measured during prolonged exercise to exhaustion in both dehydrated and euhydrated states. After a rise at the onset of exercise, ICA flow declined to baseline with progressive dehydration (P < 0.05). However, cerebral metabolism remained stable through enhanced oxygen and glucose extraction (P < 0.05). ECA flow increased for one hour but declined prior to exhaustion. Fluid ingestion maintained cerebral and extra-cranial perfusion throughout non-fatiguing exercise. During exhaustive exercise, however, euhydration delayed but did not prevent the decline in cerebral perfusion. In conclusion, during prolonged exercise in the heat dehydration accelerates the decline in CBF without affecting CMRO2 and also restricts extra-cranial perfusion. Thus fatigue is related to reduction in CBF and extra-cranial perfusion rather than in CMRO2.The study was supported by a grant from the Gatorade Sports Science Institute, PepsiCo Inc, USA
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