476 research outputs found
Ultracold atoms in optical lattices
Bosonic atoms trapped in an optical lattice at very low temperatures, can be
modeled by the Bose-Hubbard model. In this paper, we propose a slave-boson
approach for dealing with the Bose-Hubbard model, which enables us to
analytically describe the physics of this model at nonzero temperatures. With
our approach the phase diagram for this model at nonzero temperatures can be
quantified.Comment: 29 pages, 10 figure
Mott insulators in an optical lattice with high filling factors
We discuss the superfluid to Mott insulator transition of an atomic Bose gas
in an optical lattice with high filling factors. We show that also in this
multi-band situation, the long-wavelength physics is described by a single-band
Bose-Hubbard model. We determine the many-body renormalization of the tunneling
and interaction parameters in the effective Bose-Hubbard Hamiltonian, and
consider the resulting model at nonzero temperatures. We show that in
particular for a one or two-dimensional optical lattice, the Mott insulator
phase is more difficult to realize than anticipated previously.Comment: 5 pages, 3 figures, title changed, major restructuring, resubmitted
to PR
Tissue-Specific RNAi Tools to Identify Components for Systemic Stress Signaling
Over the past decade there has been a transformative increase in knowledge surrounding the regulation of protein quality control processes, unveiling the importance of intercellular signaling processes in the regulation of cell-nonautonomous proteostasis. Recent studies are now beginning to uncover signaling components and pathways that coordinate protein quality control from one tissue to another. It is therefore important to identify mechanisms and components of the cell-nonautonomous proteostasis network (PN) and its relevance for aging, stress responses and protein misfolding diseases. In the laboratory, we use genetic knockdown by tissue-specific RNAi in combination with stress reporters and tissue-specific proteostasis sensors to study this. We describe methodologies to examine and to identify components of the cell-nonautonomous PN that can act in tissues perceiving a stress condition and in responding cells to activate a protective response. We first describe how to generate hairpin RNAi constructs for constitutive genetic knockdown in specific tissues and how to perform tissue-specific genetic knockdown by feeding RNAi at different life stages. Stress reporters and behavioral assays function as valuable readouts that enable the fast screening of genes and conditions modifying systemic stress signaling processes. Finally, proteostasis sensors expressed in different tissues are utilized to determine changes in the tissue-specific capacity of the PN at different stages of development and aging. Thus, these tools should help clarify and allow monitoring the capacity of PN in specific tissues, while helping to identify components that function in different tissues to mediate cell-nonautonomous PN in an organism
On the Role of Penning Ionization in Photoassociation Spectroscopy
We study the role of Penning ionization on the photoassociation spectra of
He(^3S)-He(^3S). The experimental setup is discussed and experimental results
for different intensities of the probe laser are shown. For modelling the
experimental results we consider coupled-channel calculations of the crossing
of the ground state with the excited state at the Condon point. The
coupled-channel calculations are first applied to model systems, where we
consider two coupled channels without ionization, two coupled channels with
ionization, and three coupled channels, for which only one of the excited
states is ionizing. Finally, coupled-channel calculations are applied to
photoassociation of He(^3S)-He(^3S) and good agreement is obtained between the
model and the experimental results.Comment: 14 pages, 18 figures, submitted to the special issue on Cold
Molecules of J. Phys.
Loops versus lines and the compression stiffening of cells
Both animal and plant tissue exhibit a nonlinear rheological phenomenon known
as compression stiffening, or an increase in moduli with increasing uniaxial
compressive strain. Does such a phenomenon exist in single cells, which are the
building blocks of tissues? One expects an individual cell to compression
soften since the semiflexible biopolymer-based cytoskeletal network maintains
the mechanical integrity of the cell and in vitro semiflexible biopolymer
networks typically compression soften. To the contrary, we find that mouse
embryonic fibroblasts (mEFs) compression stiffen under uniaxial compression via
atomic force microscopy (AFM) studies. To understand this finding, we uncover
several potential mechanisms for compression stiffening. First, we study a
single semiflexible polymer loop modeling the actomyosin cortex enclosing a
viscous medium modeled as an incompressible fluid. Second, we study a
two-dimensional semiflexible polymer/fiber network interspersed with
area-conserving loops, which are a proxy for vesicles and fluid-based
organelles. Third, we study two-dimensional fiber networks with
angular-constraining crosslinks, i.e. semiflexible loops on the mesh scale. In
the latter two cases, the loops act as geometric constraints on the fiber
network to help stiffen it via increased angular interactions. We find that the
single semiflexible polymer loop model agrees well with our AFM experiments
until approximately 35% compressive strain. We also find for the fiber network
with area-conserving loops model that the stress-strain curves are sensitive to
the packing fraction and size distribution of the area-conserving loops,
thereby creating a mechanical fingerprint across different cell types. Finally,
we make comparisons between this model and experiments on fibrin networks
interlaced with beads as well as discuss the tissue-scale implications of
cellular compression stiffening.Comment: 19 pages, 17 figure
Excitations of a Bose-Einstein condensate in a one-dimensional optical lattice
We investigate the low-lying excitations of a stack of weakly-coupled
two-dimensional Bose-Einstein condensates that is formed by a one-dimensional
optical lattice. In particular, we calculate the dispersion relations of the
monopole and quadrupole modes, both for the ground state as well as for the
case in which the system contains a vortex along the direction of the lasers
creating the optical lattice. Our variational approach enables us to determine
analytically the dispersion relations for an arbitrary number of atoms in every
two-dimensional condensate and for an arbitrary momentum. We also discuss the
feasibility of experimentally observing our results.Comment: 16 pages, 5 figures, minor changes,accepted for publication in Phys.
Rev.
Increased levels of Stress-inducible phosphoprotein-1 accelerates amyloid-β deposition in a mouse model of Alzheimer’s disease
Molecular chaperones and co-chaperones, which are part of the protein quality control machinery, have been shown to regulate distinct aspects of Alzheimer’s Disease (AD) pathology in multiple ways. Notably, the co-chaperone STI1, which presents increased levels in AD, can protect mammalian neurons from amyloid-β toxicity in vitro and reduced STI1 levels worsen Aβ toxicity in C. elegans. However, whether increased STI1 levels can protect neurons in vivo remains unknown. We determined that overexpression of STI1 and/or Hsp90 protected C. elegans expressing Aβ(3–42) against Aβ-mediated paralysis. Mammalian neurons were also protected by elevated levels of endogenous STI1 in vitro, and this effect was mainly due to extracellular STI1. Surprisingly, in the 5xFAD mouse model of AD, by overexpressing STI1, we find increased amyloid burden, which amplifies neurotoxicity and worsens spatial memory deficits in these mutants. Increased levels of STI1 disturbed the expression of Aβ-regulating enzymes (BACE1 and MMP-2), suggesting potential mechanisms by which amyloid burden is increased in mice. Notably, we observed that STI1 accumulates in dense-core AD plaques in both 5xFAD mice and human brain tissue. Our findings suggest that elevated levels of STI1 contribute to Aβ accumulation, and that STI1 is deposited in AD plaques in mice and humans. We conclude that despite the protective effects of STI1 in C. elegans and in mammalian cultured neurons, in vivo, the predominant effect of elevated STI1 is deleterious in AD
Transmittivity of a Bose-Einstein condensate on a lattice: interference from period doubling and the effect of disorder
We evaluate the particle current flowing in steady state through a
Bose-Einstein condensate subject to a constant force in a quasi-onedimensional
lattice and to attractive interactions from fermionic atoms that are localized
in various configurations inside the lattice wells. The system is treated
within a Bose-Hubbard tight binding model by an out-of-equilibrium Green's
function approach. A new band gap opens up when the lattice period is doubled
by locating the fermions in alternate wells and yields an interference pattern
in the transmittivity on varying the intensity of the driving force. The
positions of the transmittivity minima are determined by matching the period of
Bloch oscillations and the time for tunnelling across the band gap. Massive
disorder in the distribution of the fermions will wash out the interference
pattern, but the same period doubling of the lattice can be experimentally
realized in a four-beam set-up. We report illustrative numerical results for a
mixture of 87Rb and 40K atoms in an optical lattice created by laser beams with
a wavelength of 763 nm.Comment: 13 pages, 5 figure
Predictors of Societal Costs of Older Care-Dependent Adults Living in the Community in 11 European Countries
BACKGROUND: The objective was to identify predictors of societal costs covering formal and informal care utilization by older home care clients in 11 European countries. METHODS : Societal costs of 1907 older clients receiving home care for 12 months from the Aged in Home care (AdHoc) study were estimated using the InterRAI Minimum Data Set for Home Care's (MDS-HC) resource use items. Predictors (medical, functional, and psychosocial domains) of societal costs were identified by performing univariate and multivariate generalized linear model analyses. RESULTS : Mean societal costs per participant were (sic)36 442, ranging from (sic)14 865 in Denmark to (sic)78 836 in the United Kingdom. In the final multivariate model, country, being married, activities of daily living (ADL) dependency, cognitive impairment, limitations of going out, oral conditions, number of medications, arthritis, and cerebro vascular accident (CVA) were significantly associated with societal costs. CONCLUSIONS: Of the predictors, ADL dependency and limitations of going out may be modifiable. Developing interventions targeted at improving these conditions may create opportunities to curtail societal costs.Peer reviewe
First evaluation of a commercial multiplex PCR panel for rapid detection of pathogens associated with acute joint infections
Background: prompt recognition and identification of the causative
microorganism in acute septic arthritis of native and prosthetic joints is
vital to increase the chances of successful treatment. The aim of this study
was to independently assess the diagnostic accuracy of the multiplex
BIOFIRE® Joint Infection (JI) Panel
(investigational use only) in synovial fluid for rapid diagnosis.
Methods: synovial fluid samples were collected at the University
Medical Center Groningen from patients who had a clinical suspicion of a
native septic arthritis, early acute (post-operative, within 3 months after
arthroplasty) periprosthetic joint infection (PJI) or late acute
(hematogenous, ≥3 months after arthroplasty) PJI. JI Panel results
were compared to infection according to Musculoskeletal Infection Society
criteria and culture-based methods as reference standard. Results:
a total of 45 samples were analysed. The BIOFIRE JI Panel showed a high
specificity (100 %, 95 % confidence interval (CI): 78–100) in all patient categories.
Sensitivity was 83 % (95 % CI: 44–97) for patients with a clinical
suspicion of native septic arthritis (n=12), 73 % (95 % CI: 48–89)
for patients with a clinical suspicion of a late acute PJI (n=14), and
30 % (95 % CI: 11–60) for patients with a clinical suspicion of an
early acute PJI (n=19). Conclusion: the results of this study
indicate a clear clinical benefit of the BIOFIRE JI Panel in patients with a
suspected native septic arthritis and late acute (hematogenous) PJI, but a
low clinical benefit in patients with an early acute (post-operative) PJI
due to the absence of certain relevant microorganisms, such as
Staphylococcus epidermidis, from the panel.</p
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