1,502 research outputs found
Universality of modulation length (and time) exponents
We study systems with a crossover parameter lambda, such as the temperature
T, which has a threshold value lambda* across which the correlation function
changes from exhibiting fixed wavelength (or time period) modulations to
continuously varying modulation lengths (or times). We report on a new
exponent, nuL, characterizing the universal nature of this crossover. These
exponents, similar to standard correlation length exponents, are obtained from
motion of the poles of the momentum (or frequency) space correlation functions
in the complex k-plane (or omega-plane) as the parameter lambda is varied. Near
the crossover, the characteristic modulation wave-vector KR on the variable
modulation length "phase" is related to that on the fixed modulation length
side, q via |KR-q|\propto|T-T*|^{nuL}. We find, in general, that nuL=1/2. In
some special instances, nuL may attain other rational values. We extend this
result to general problems in which the eigenvalue of an operator or a pole
characterizing general response functions may attain a constant real (or
imaginary) part beyond a particular threshold value, lambda*. We discuss
extensions of this result to multiple other arenas. These include the ANNNI
model. By extending our considerations, we comment on relations pertaining not
only to the modulation lengths (or times) but also to the standard correlation
lengths (or times). We introduce the notion of a Josephson timescale. We
comment on the presence of "chaotic" modulations in "soft-spin" and other
systems. These relate to glass type features. We discuss applications to Fermi
systems - with particular application to metal to band insulator transitions,
change of Fermi surface topology, divergent effective masses, Dirac systems,
and topological insulators. Both regular periodic and glassy (and spatially
chaotic behavior) may be found in strongly correlated electronic systems.Comment: 22 pages, 15 figure
The Fermi Problem in Discrete Systems
The Fermi two-atom problem illustrates an apparent causality violation in
Quantum Field Theory which has to do with the nature of the built in
correlations in the vacuum. It has been a constant subject of theoretical
debate and discussions during the last few decades. Nevertheless, although the
issues at hand could in principle be tested experimentally, the smallness of
such apparent violations of causality in Quantum Electrodynamics prevented the
observation of the predicted effect. In the present paper we show that the
problem can be simulated within the framework of discrete systems that can be
manifested, for instance, by trapped atoms in optical lattices or trapped ions.
Unlike the original continuum case, the causal structure is no longer sharp.
Nevertheless, as we show, it is possible to distinguish between "trivial"
effects due to "direct" causality violations, and the effects associated with
Fermi's problem, even in such discrete settings. The ability to control
externally the strength of the atom-field interactions, enables us also to
study both the original Fermi problem with "bare atoms", as well as correction
in the scenario that involves "dressed" atoms. Finally, we show that in
principle, the Fermi effect can be detected using trapped ions.Comment: Second version - minor change
Explaining the Frequency of Alcohol Consumption in a Conflict Zone: Jews and Palestinians in Israel
Experiencing stress and exposure to terrorism may have an adverse effect on health risk behaviors. Few studies have examined alcohol use among adults living in Israel under chronic, stressful terrorism-related conditions. In this study, we examined the relationships of demographics, past stressful events, and terrorism exposure to the frequency of alcohol use and the mediating roles of depressive and post-traumatic stress disorder (PTSD) symptoms. We used three waves of data from a 2007–2008 nationally representative sample of Jewish and Palestinian adults in Israel. We assessed past stressful events, in addition to direct and indirect exposures to terrorism. Results indicated that past stressful events and exposure to terrorism were not directly associated with alcohol use, but were indirectly associated and mediated by depressive and PTSD symptomology. Mental health symptoms were differentially associated with alcohol use. More frequent drinking was mediated by higher levels of depression, including for women and Palestinians; however, PTSD symptom severity was related to less frequent drinking. Mental health may play a prominent role in the frequency of alcohol use among adults exposed to terrorism in Israel. Alcohol use, as a coping mechanism, may differ by demographic characteristics (gender and ethnicity) and psychological symptomology for adults living in a conflict zone in Israel
Bond Algebras and Exact Solvability of Hamiltonians: Spin S=1/2 Multilayer Systems and Other Curiosities
We introduce an algebraic methodology for designing exactly-solvable Lie
model Hamiltonians. The idea consists in looking at the algebra generated by
bond operators. We illustrate how this method can be applied to solve numerous
problems of current interest in the context of topological quantum order. These
include Kitaev's toric code and honeycomb models, a vector exchange model, and
a Clifford gamma model on a triangular lattice.Comment: 12 pages, 5 figure
Voltage dependence of Landau-Lifshitz-Gilbert damping of a spin in a current driven tunnel junction
We present a theory of Landau-Lifshitz-Gilbert damping for a
localized spin in the junction coupled to the conduction electrons
in both leads under an applied volatege . We find the voltage dependence of
the damping term reflecting the energy dependence of the density of states. We
find the effect is linear in the voltage and cotrolled by particle-hole
asymmetry of the leads.Comment: 6 pages, 3 figure
Evolutionary Selection Against Short Nucleotide Sequences in Viruses and Their Related Hosts
Viruses are under constant evolutionary pressure to effectively interact with the host intracellular factors, while evading its immune system. Understanding how viruses co-evolve with their hosts is a fundamental topic in molecular evolution and may also aid in developing novel viral based applications such as vaccines, oncologic therapies, and anti-bacterial treatments. Here, based on a novel statistical framework and a large-scale genomic analysis of 2,625 viruses from all classes infecting 439 host organisms from all kingdoms of life, we identify short nucleotide sequences that are under-represented in the coding regions of viruses and their hosts. These sequences cannot be explained by the coding regions’ amino acid content, codon, and dinucleotide frequencies. We specifically show that short homooligonucleotide and palindromic sequences tend to be under-represented in many viruses probably due to their effect on gene expression regulation and the interaction with the host immune system. In addition, we show that more sequences tend to be under-represented in dsDNA viruses than in other viral groups. Finally, we demonstrate, based on in vitro and in vivo experiments, how under-represented sequences can be used to attenuated Zika virus strains
Exact results on the Kitaev model on a hexagonal lattice: spin states, string and brane correlators, and anyonic excitations
In this work, we illustrate how a Jordan-Wigner transformation combined with
symmetry considerations enables a direct solution of Kitaev's model on the
honeycomb lattice. We (i) express the p-wave type fermionic ground states of
this system in terms of the original spins, (ii) adduce that symmetry alone
dictates the existence of string and planar brane type correlators and their
composites, (iii) compute the value of such non-local correlators by employing
the Jordan-Wigner transformation, (iv) affirm that the spectrum is
inconsequential to the existence of topological quantum order and that such
information is encoded in the states themselves, and (v) express the anyonic
character of the excitations in this system and the local symmetries that it
harbors in terms of fermions.Comment: 14 pages, 7 figure
Renormalization, duality, and phase transitions in two- and three-dimensional quantum dimer models
We derive an extended lattice gauge theory type action for quantum dimer
models and relate it to the height representations of these systems. We examine
the system in two and three dimensions and analyze the phase structure in terms
of effective theories and duality arguments. For the two-dimensional case we
derive the effective potential both at zero and finite temperature. The
zero-temperature theory at the Rokhsar-Kivelson (RK) point has a critical point
related to the self-dual point of a class of models in the
limit. Two phase transitions featuring a fixed line are shown to appear in the
phase diagram, one at zero temperature and at the RK point and another one at
finite temperature above the RK point. The latter will be shown to correspond
to a Kosterlitz-Thouless (KT) phase transition, while the former will be
governed by a KT-like universality class, i.e., sharing many features with a KT
transition but actually corresponding to a different universality class. On the
other hand, we show that at the RK point no phase transition happens at finite
temperature. For the three-dimensional case we derive the corresponding dual
gauge theory model at the RK point. We show in this case that at zero
temperature a first-order phase transition occurs, while at finite temperatures
both first- and second-order phase transitions are possible, depending on the
relative values of the couplings involved.Comment: 16 pages, 3 figure
Strontium and Oxygen Isotope Analyses Reveal Late Cretaceous Shark Teeth in Iron Age Strata in the Southern Levant
Skeletal remains in archaeological strata are often assumed to be of similar ages. Here we show that combined Sr and O isotope analyses can serve as a powerful tool for assessing fish provenance and even for identifying fossil fish teeth in archaeological contexts. For this purpose, we established a reference Sr and O isotope dataset of extant fish teeth from major water bodies in the Southern Levant. Fossil shark teeth were identified within Iron Age cultural layers dating to 8–9th century BCE in the City of David, Jerusalem, although the reason for their presence remains unclear. Their enameloid 87Sr/86Sr and δ18OPO4 values [0.7075 ± 0.0001 (1 SD, n = 7) and 19.6 ± 0.9‰ (1 SD, n = 6), respectively], are both much lower than values typical for modern marine sharks from the Mediterranean Sea [0.7092 and 22.5–24.6‰ (n = 2), respectively]. The sharks’ 87Sr/86Sr are also lower than those of rain- and groundwater as well as the main soil types in central Israel (≥0.7079). This indicates that these fossil sharks incorporated Sr (87Sr/86Sr ≈ 0.7075) from a marine habitat with values typical for Late Cretaceous seawater. This scenario is in line with the low shark enameloid δ18OPO4 values reflecting tooth formation in the warm tropical seawater of the Tethys Ocean. Age estimates using 87Sr/86Sr stratigraphy place these fossil shark teeth at around 80-million-years-old. This was further supported by their taxonomy and the high dentine apatite crystallinity, low organic carbon, high U and Nd contents, characteristics that are typical for fossil specimens, and different from those of archaeological Gilthead seabream (Sparus aurata) teeth from the same cultural layers and another Chalcolithic site (Gilat). Chalcolithic and Iron Age seabream enameloid has seawater-like 87Sr/86Sr of 0.7091 ± 0.0001 (1 SD, n = 6), as expected for modern marine fish. Fossil shark and archaeological Gilthead seabream teeth both preserve original, distinct enameloid 87Sr/86Sr and δ18OPO4 signatures reflecting their different aquatic habitats. Fifty percent of the analysed Gilthead seabream teeth derive from hypersaline seawater, indicating that these seabreams were exported from the hypersaline Bardawil Lagoon in Sinai (Egypt) to the Southern Levant since the Iron Age period and possibly even earlier
mu and General Gauge Mediation
We address the mu-problem in the context of General Gauge Mediation (GGM). We
classify possible models depending on the way the Higgs fields couple to the
supersymmetry breaking hidden-sector. The different types of models have
distinct signatures in the MSSM parameters. We find concrete and surprisingly
simple examples based on messengers in each class. These examples lead to all
the soft masses and a consistent Higgs-sector.Comment: 21 pages. v2: minor corrections. v3: added referenc
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