158 research outputs found
Memory effects in classical and quantum mean-field disordered models
We apply the Kovacs experimental protocol to classical and quantum p-spin
models. We show that these models have memory effects as those observed
experimentally in super-cooled polymer melts. We discuss our results in
connection to other classical models that capture memory effects. We propose
that a similar protocol applied to quantum glassy systems might be useful to
understand their dynamics.Comment: 24 pages, 12 figure
Static properties of the dissipative random quantum Ising ferromagnetic chain
We study the zero temperature static properties of dissipative ensembles of
quantum Ising spins arranged on periodic one dimensional finite clusters and on
an infinite chain. The spins interact ferro-magnetically with nearest-neighbour
pure and random couplings. They are subject to a transverse field and coupled
to an Ohmic bath of quantum harmonic oscillators. We analyze the coupled system
using Monte Carlo simulations of the classical two-dimensional counterpart
model. The coupling to the bath enhances the extent of the ordered phase, as
found in mean-field spin-glasses. In the case of finite clusters we show that a
generalization of the Caldeira-Leggett localization transition exists. In the
case of the infinite random chain we study the effect of dissipation on the
transition and the Griffiths phase.Comment: 21 pages, 10 figure
Effects of dissipation on disordered quantum spin models
We study the effects of the coupling to an Ohmic quantum reservoir on the
static and dynamical properties of a family of disordered SU(2) spin models in
a transverse magnetic field using a method of direct spin summation. The
tendency to form a glassy phase increases with the strength of the coupling of
the system to the environment. We study the influence of the environment on the
features of the phase diagram of the various models as well as the stability of
the possible phases.Comment: 24 pages, 8 fig
Mycofactocin Is Associated with Ethanol Metabolism in Mycobacteria
Tuberculosis is caused by Mycobacterium tuberculosis, and the increasing emergence of multidrug-resistant strains renders current treatment options ineffective. Although new antimycobacterial drugs are urgently required, their successful development often relies on complete understanding of the metabolic pathwaysâe.g., cholesterol assimilationâthat are critical for persistence and for pathogenesis of M. tuberculosis. In this regard, mycofactocin (MFT) function appears to be important because its biosynthesis genes are predicted to be essential for M. tuberculosisin vitro growth in cholesterol. In determining the metabolic basis of this genetic requirement, our results unexpectedly revealed the essential function of MFT in ethanol metabolism. The metabolic dysfunction thereof was found to affect the mycobacterial growth in cholesterol which is solubilized by ethanol. This knowledge is fundamental in recognizing the bona fide function of MFT, which likely resembles the pyrroloquinoline quinone-dependent ethanol oxidation in acetic acid bacteria exploited for industrial production of vinegar.Mycofactocin (MFT) belongs to the class of ribosomally synthesized and posttranslationally modified peptides conserved in many Actinobacteria. Mycobacterium tuberculosis assimilates cholesterol during chronic infection, and its in vitro growth in the presence of cholesterol requires most of the MFT biosynthesis genes (mftA, mftB, mftC, mftD, mftE, and mftF), although the reasons for this requirement remain unclear. To identify the function of MFT, we characterized MFT biosynthesis mutants constructed in Mycobacterium smegmatis, M. marinum, and M. tuberculosis. We found that the growth deficit of mft deletion mutants in medium containing cholesterolâa phenotypic basis for gene essentiality predictionâdepends on ethanol, a solvent used to solubilize cholesterol. Furthermore, functionality of MFT was strictly required for growth of free-living mycobacteria in ethanol and other primary alcohols. Among other genes encoding predicted MFT-associated dehydrogenases, MSMEG_6242 was indispensable for M. smegmatis ethanol assimilation, suggesting that it is a candidate catalytic interactor with MFT. Despite being a poor growth substrate, ethanol treatment resulted in a reductive cellular state with NADH accumulation in M. tuberculosis. During ethanol treatment, mftC mutant expressed the transcriptional signatures that are characteristic of respirational dysfunction and a redox-imbalanced cellular state. Counterintuitively, there were no differences in cellular bioenergetics and redox parameters in mftC mutant cells treated with ethanol. Therefore, further understanding of the function of MFT in ethanol metabolism is required to identify the cause of growth retardation of MFT mutants in cholesterol. Nevertheless, our results establish the physiological role of MFT and also provide new insights into the specific functions of MFT homologs in other actinobacterial systems
requirements for naive CD4+ T cell stimulation
Human primary dendritic cells (DCs) are heterogeneous by phenotype, function,
and tissue localization and distinct from inflammatory monocyte-derived DCs.
Current information regarding the susceptibility and functional role of
primary human DC subsets to Mycobacterium tuberculosis (Mtb) infection is
limited. Here, we dissect the response of different primary DC subsets to Mtb
infection. Myeloid CD11c+ cells and pDCs (C-type lectin 4C+ cells) were
located in human lymph nodes (LNs) of tuberculosis (TB) patients by
histochemistry. Rare CD141hi DCs (C-type lectin 9A+ cells) were also
identified. Infection with live Mtb revealed a higher responsiveness of
myeloid CD1c+ DCs compared to CD141hi DCs and pDCs. CD1c+ DCs produced
interleukin (IL)-6, tumor necrosis factor α, and IL-1ÎČ but not IL-12p70, a
cytokine important for Th1 activation and host defenses against Mtb. Yet,
CD1c+ DCs were able to activate autologous naĂŻve CD4+ T cells. By combining
cell purification with fluorescence-activated cell sorting and gene expression
profiling on rare cell populations, we detected in responding CD4+ T cells,
genes related to effector-cytolytic functions and transcription factors
associated with Th1, Th17, and Treg polarization, suggesting multifunctional
properties in our experimental conditions. Finally, immunohistologic analyses
revealed contact between CD11c+ cells and pDCs in LNs of TB patients and in
vitro data suggest that cooperation between Mtb-infected CD1c+ DCs and pDCs
favors stimulation of CD4+ T cells
Comparison of the LUNA 3He(alpha,gamma)7Be activation results with earlier measurements and model calculations
Recently, the LUNA collaboration has carried out a high precision measurement
on the 3He(alpha,gamma)7Be reaction cross section with both activation and
on-line gamma-detection methods at unprecedented low energies. In this paper
the results obtained with the activation method are summarized. The results are
compared with previous activation experiments and the zero energy extrapolated
astrophysical S factor is determined using different theoretical models.Comment: Accepted for publication in Journal of Physics
Activation measurement of the 3He(alpha,gamma)7Be cross section at low energy
The nuclear physics input from the 3He(alpha,gamma)7Be cross section is a
major uncertainty in the fluxes of 7Be and 8B neutrinos from the Sun predicted
by solar models and in the 7Li abundance obtained in big-bang nucleosynthesis
calculations. The present work reports on a new precision experiment using the
activation technique at energies directly relevant to big-bang nucleosynthesis.
Previously such low energies had been reached experimentally only by the
prompt-gamma technique and with inferior precision. Using a windowless gas
target, high beam intensity and low background gamma-counting facilities, the
3He(alpha,gamma)7Be cross section has been determined at 127, 148 and 169 keV
center-of-mass energy with a total uncertainty of 4%. The sources of systematic
uncertainty are discussed in detail. The present data can be used in big-bang
nucleosynthesis calculations and to constrain the extrapolation of the
3He(alpha,gamma)7Be astrophysical S-factor to solar energies
The 3He(alpha,gamma)7Be S-factor at solar energies: the prompt gamma experiment at LUNA
The 3He(alpha,gamma)7Be process is a key reaction in both Big-Bang
nucleosynthesis and p-p chain of Hydrogen Burning in Stars. A new measurement
of the 3He(alpha,gamma)7Be cross section has been performed at the INFN Gran
Sasso underground laboratory by both the activation and the prompt gamma
detection methods. The present work reports full details of the prompt gamma
detection experiment, focusing on the determination of the systematic
uncertainty. The final data, including activation measurements at LUNA, are
compared with the results of the last generation experiments and two different
theoretical models are used to obtain the S-factor at solar energies.Comment: Accepted for publication in Nucl. Phys.
NLRC5 promotes transcription of BTN3A1-3 genes and VÎł9VÎŽ2 T cell-mediated killing
BTN3A molecules-BTN3A1 in particular-emerged as important mediators of VÎł9VÎŽ2 T cell activation by phosphoantigens. These metabolites can originate from infections, e.g. with Mycobacterium tuberculosis, or by alterations in cellular metabolism. Despite the growing interest in the BTN3A genes and their high expression in immune cells and various cancers, little is known about their transcriptional regulation. Here we show that these genes are induced by NLRC5, a regulator of MHC class I gene transcription, through an atypical regulatory motif found in their promoters. Accordingly, a robust correlation between NLRC5 and BTN3A gene expression was found in healthy, in M. tuberculosis-infected donors' blood cells, and in primary tumors. Moreover, forcing NLRC5 expression promoted VÎł9VÎŽ2 T-cell-mediated killing of tumor cells in a BTN3A-dependent manner. Altogether, these findings indicate that NLRC5 regulates the expression of BTN3A genes and hence open opportunities to modulate antimicrobial and anticancer immunity
Ultra-sensitive in-beam gamma-ray spectroscopy for nuclear astrophysics at LUNA
Ultra-sensitive in-beam gamma-ray spectroscopy studies for nuclear
astrophysics are performed at the LUNA (Laboratory for Underground Nuclear
Astrophysics) 400 kV accelerator, deep underground in Italy's Gran Sasso
laboratory. By virtue of a specially constructed passive shield, the laboratory
gamma-ray background for E_\gamma < 3 MeV at LUNA has been reduced to levels
comparable to those experienced in dedicated offline underground gamma-counting
setups. The gamma-ray background induced by an incident alpha-beam has been
studied. The data are used to evaluate the feasibility of sensitive in-beam
experiments at LUNA and, by extension, at similar proposed facilities.Comment: accepted, Eur. Phys. J.
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