3,967 research outputs found
Topological Quantum Glassiness
Quantum tunneling often allows pathways to relaxation past energy barriers
which are otherwise hard to overcome classically at low temperatures. However,
this is not always the case. In this paper we provide simple exactly solvable
examples where the barriers each system encounters on its approach to lower and
lower energy states become increasingly large and eventually scale with the
system size. If the environment couples locally to the physical degrees of
freedom in the system, tunnelling under large barriers requires processes whose
order in perturbation theory is proportional to the width of the barrier. This
results in quantum relaxation rates that are exponentially suppressed in system
size: For these quantum systems, no physical bath can provide a mechanism for
relaxation that is not dynamically arrested at low temperatures. The examples
discussed here are drawn from three dimensional generalizations of Kitaev's
toric code, originally devised in the context of topological quantum computing.
They are devoid of any local order parameters or symmetry breaking and are thus
examples of topological quantum glasses. We construct systems that have slow
dynamics similar to either strong or fragile glasses. The example with
fragile-like relaxation is interesting in that the topological defects are
neither open strings or regular open membranes, but fractal objects with
dimension .Comment: (18 pages, 4 figures, v2: typos and updated figure); Philosophical
Magazine (2011
Physiotherapists implicitly evaluate bending and lifting with a round back as dangerous
© 2018 Elsevier Ltd. Background: Beliefs can be assessed using explicit measures (e.g. questionnaires) that rely on information of which the person is ‘aware’ and willing to disclose. Conversely, implicit measures evaluate beliefs using computer-based tasks that allow reduced time for introspection thus reflecting ‘automatic’ associations. Thus far, physiotherapists’ beliefs about back posture and safety have not been evaluated with implicit measures. Objectives: (1) Evaluate implicit associations between bending lifting back posture (straight-back vs round-back) and safety (safe vs danger); (2) Explore correlations between implicit and explicit measures of beliefs towards vulnerability of the back. Design: Exploratory cross-sectional quantitative study. Methods: 47 musculoskeletal physiotherapists completed explicit measures of fear of movement (TSK-HC), back beliefs (BackPAQDanger) and beliefs related to bending and lifting back posture and safety (BSB). An Implicit Association Test (IAT) was used to assess implicit associations between (i) images of people bending/lifting with a ‘round-back’ or with a ‘straight-back’ posture, and (ii) words representing ‘safety’ and ‘danger’. A one-sample t-test assessed the degree and direction of the sample's IAT score. Cohen's d provided an effect size of the estimated bias. Correlation between IAT and each explicit measure was assessed using Pearson's coefficient. Results: The sample displayed an implicit association between ‘round-back’ and ‘danger’ (µ = 0.213, 95% CI [0.075-0.350], p =.003), with an effect size magnitude of 0.45. There were fair to moderate correlations between IAT and BSB (r = 0.320, 95% CI [0.036-0.556], p =.029) and, IAT and BackPAQDanger (r = 0.413, 95%CI [0.143-0.626], p =.004). Conclusions: Physiotherapists displayed an implicit bias towards bending and lifting with a round-back as dangerous
Neutralisation of SARS-CoV-2 by monoclonal antibody through dual targeting powder formulation
Neutralising monoclonal antibody (mAb) is an important weapon in our arsenal for combating respiratory viral infections. However, the effectiveness of neutralising mAb has been impeded by the rapid emergence of mutant variants. Early administration of broad-spectrum mAb with improved delivery efficiency can potentially enhance efficacy and patient outcomes. WKS13 is a humanised mAb which was previously demonstrated to exhibit broad-spectrum activity against SARS-CoV-2 variants. In this study, a dual targeting formulation strategy was designed to deliver WKS13 to both the nasal cavity and lower airways, the two critical sites of infection caused by SARS-CoV-2. Dry powders of WKS13 were first prepared by spray drying, with cyclodextrin used as stabiliser excipient. Two-fluid nozzle (TFN) was used to produce particles below 5 μm for lung deposition (C-TFN formulation) and ultrasonic nozzle (USN) was used to produce particles above 10 μm for nasal deposition (C-USN formulation). Gel electrophoresis and size exclusion chromatography studies showed that the structural integrity of mAb was successfully preserved with no sign of aggregation after spray drying. To achieve dual targeting property, C-TFN and C-USN were mixed at various ratios. The aerosolisation property of the mixed formulations dispersed from a nasal powder device was examined using a Next Generation Impactor (NGI) coupled with a glass expansion chamber. When the ratio of C-TFN in the mixed formulation increased, the fraction of particles deposited in the lung increased proportionally while the fraction of particles deposited in the nasal cavity decreased correspondingly. A customisable aerosol deposition profile could therefore be achieved by manipulating the mixing ratio between C-TFN and C-USN. Dual administration of C-TFN and C-USN powders to the lung and nasal cavity of hamsters, respectively, was effective in offering prophylactic protection against SARS-CoV-2 Delta variant. Viral loads in both the lung tissues and nasal wash were significantly reduced, and the efficacy was comparable to systemic administration of unformulated WKS13. Overall, dual targeting powder formulation of neutralising mAb is a promising approach for prophylaxis of respiratory viral infections. The ease and non-invasive administration of dual targeting nasal powder may facilitate the widespread distribution of neutralising mAb during the early stage of unpredictable outbreaks
Can ultrasound be used to stimulate nerve tissue?
BACKGROUND: The stimulation of nerve or cortical tissue by magnetic induction is a relatively new tool for the non-invasive study of the brain and nervous system. Transcranial magnetic stimulation (TMS), for example, has been used for the functional mapping of the motor cortex and may have potential for treating a variety of brain disorders. METHODS AND RESULTS: A new method of stimulating active tissue is proposed by propagating ultrasound in the presence of a magnetic field. Since tissue is conductive, particle motion created by an ultrasonic wave will induce an electric current density generated by Lorentz forces. An analytical derivation is given for the electric field distribution induced by a collimated ultrasonic beam. An example shows that peak electric fields of up to 8 V/m appear to be achievable at the upper range of diagnostic intensities. This field strength is about an order of magnitude lower than fields typically associated with TMS; however, the electric field gradients induced by ultrasound can be quite high (about 60 kV/m(2 )at 4 MHz), which theoretically play a more important role in activation than the field magnitude. The latter value is comparable to TMS-induced gradients. CONCLUSION: The proposed method could be used to locally stimulate active tissue by inducing an electric field in regions where the ultrasound is focused. Potential advantages of this method compared to TMS is that stimulation of cortical tissue could be highly localized as well as achieved at greater depths in the brain than is currently possible with TMS
Lattice potentials and fermions in holographic non Fermi-liquids: hybridizing local quantum criticality
We study lattice effects in strongly coupled systems of fermions at a finite
density described by a holographic dual consisting of fermions in
Anti-de-Sitter space in the presence of a Reissner-Nordstrom black hole. The
lattice effect is encoded by a periodic modulation of the chemical potential
with a wavelength of order of the intrinsic length scales of the system. This
corresponds with a highly complicated "band structure" problem in AdS, which we
only manage to solve in the weak potential limit. The "domain wall" fermions in
AdS encoding for the Fermi surfaces in the boundary field theory diffract as
usually against the periodic lattice, giving rise to band gaps. However, the
deep infrared of the field theory as encoded by the near horizon AdS2 geometry
in the bulk reacts in a surprising way to the weak potential. The hybridization
of the fermions bulk dualizes into a linear combination of CFT1 "local quantum
critical" propagators in the bulk, characterized by momentum dependent
exponents displaced by lattice Umklapp vectors. This has the consequence that
the metals showing quasi-Fermi surfaces cannot be localized in band insulators.
In the AdS2 metal regime, where the conformal dimension of the fermionic
operator is large and no Fermi surfaces are present at low T/\mu, the lattice
gives rise to a characteristic dependence of the energy scaling as a function
of momentum. We predict crossovers from a high energy standard momentum AdS2
scaling to a low energy regime where exponents found associated with momenta
"backscattered" to a lower Brillioun zone in the extended zone scheme. We
comment on how these findings can be used as a unique fingerprint for the
detection of AdS2 like "pseudogap metals" in the laboratory.Comment: 42 pages, 5 figures; v2, minor correction, to appear in JHE
Tracing magnetism and pairing in FeTe-based systems
In order to examine the interplay between magnetism and superconductivity, we
monitor the non- superconducting chalcogenide FeTe and follow its transitions
under insertion of oxygen, doping with Se and vacancies of Fe using
spin-polarized band structure methods (LSDA with GGA) starting from the
collinear and bicollinear magnetic arrangements. We use a supercell of Fe8Te8
as our starting point so that it can capture local changes in magnetic moments.
The calculated values of magnetic moments agree well with available
experimental data while oxygen insertions lead to significant changes in the
bicollinear or collinear magnetic moments. The total energies of these systems
indicate that the collinear-derived structure is the more favorable one prior
to a possible superconducting transition. Using a 8-site Betts-cluster-based
lattice and the Hubbard model, we show why this structure favors electron or
hole pairing and provides clues to a common understanding of charge and spin
pairing in the cuprates, pnictides and chalcogenides
Fractional quantum Hall effect in a quantum point contact at filling fraction 5/2
Recent theories suggest that the excitations of certain quantum Hall states
may have exotic braiding statistics which could be used to build topological
quantum gates. This has prompted an experimental push to study such states
using confined geometries where the statistics can be tested. We study the
transport properties of quantum point contacts (QPCs) fabricated on a
GaAs/AlGaAs two dimensional electron gas that exhibits well-developed
fractional quantum Hall effect, including at bulk filling fraction 5/2. We find
that a plateau at effective QPC filling factor 5/2 is identifiable in point
contacts with lithographic widths of 1.2 microns and 0.8 microns, but not 0.5
microns. We study the temperature and dc-current-bias dependence of the 5/2
plateau in the QPC, as well as neighboring fractional and integer plateaus in
the QPC while keeping the bulk at filling factor 3. Transport near QPC filling
factor 5/2 is consistent with a picture of chiral Luttinger liquid edge-states
with inter-edge tunneling, suggesting that an incompressible state at 5/2 forms
in this confined geometry
Holographic Superconductors from Einstein-Maxwell-Dilaton Gravity
We construct holographic superconductors from Einstein-Maxwell-dilaton
gravity in 3+1 dimensions with two adjustable couplings and the charge
carried by the scalar field. For the values of and we
consider, there is always a critical temperature at which a second order phase
transition occurs between a hairy black hole and the AdS RN black hole in the
canonical ensemble, which can be identified with the superconducting phase
transition of the dual field theory. We calculate the electric conductivity of
the dual superconductor and find that for the values of and where
is small the dual superconductor has similar properties to the
minimal model, while for the values of and where is
large enough, the electric conductivity of the dual superconductor exhibits
novel properties at low frequencies where it shows a "Drude Peak" in the real
part of the conductivity.Comment: 25 pages, 13 figures; v2, typos corrected; v3, refs added, to appear
in JHE
Generality of shear thickening in suspensions
Suspensions are of wide interest and form the basis for many smart fluids.
For most suspensions, the viscosity decreases with increasing shear rate, i.e.
they shear thin. Few are reported to do the opposite, i.e. shear thicken,
despite the longstanding expectation that shear thickening is a generic type of
suspension behavior. Here we resolve this apparent contradiction. We
demonstrate that shear thickening can be masked by a yield stress and can be
recovered when the yield stress is decreased below a threshold. We show the
generality of this argument and quantify the threshold in rheology experiments
where we control yield stresses arising from a variety of sources, such as
attractions from particle surface interactions, induced dipoles from applied
electric and magnetic fields, as well as confinement of hard particles at high
packing fractions. These findings open up possibilities for the design of smart
suspensions that combine shear thickening with electro- or magnetorheological
response.Comment: 11 pages, 9 figures, accepted for publication in Nature Material
The progesterone receptor Val660→Leu polymorphism and breast cancer risk
BACKGROUND: Recent evidence suggests a role for progesterone in breast cancer development and tumorigenesis. Progesterone exerts its effect on target cells by interacting with its receptor; thus, genetic variations, which might cause alterations in the biological function in the progesterone receptor (PGR), can potentially contribute to an individual's susceptibility to breast cancer. It has been reported that the PROGINS allele, which is in complete linkage disequilibrium with a missense substitution in exon 4 (G/T, valine→leucine, at codon 660), is associated with a decreased risk for breast cancer. METHODS: Using a nested case-control study design within the Nurses' Health Study cohort, we genotyped 1252 cases and 1660 matched controls with the use of the Taqman assay. RESULTS: We did not observe any association of breast cancer risk with carrying the G/T (Val660→Leu) polymorphism (odds ratio 1.10, 95% confidence interval 0.93–1.30). In addition, we did not observe an interaction between this allele and menopausal status and family history of breast cancer as reported previously. CONCLUSION: Overall, our study does not support an association between the Val660→Leu PROGINS polymorphism and breast cancer risk
- …