1,807 research outputs found
Classification of a supersolid: Trial wavefunctions, Symmetry breakings and Excitation spectra
A state of matter is characterized by its symmetry breaking and elementary
excitations.
A supersolid is a state which breaks both translational symmetry and internal
symmetry.
Here, we review some past and recent works in phenomenological
Ginsburg-Landau theories, ground state trial wavefunctions and microscopic
numerical calculations. We also write down a new effective supersolid
Hamiltonian on a lattice.
The eigenstates of the Hamiltonian contains both the ground state
wavefunction and all the excited states (supersolidon) wavefunctions. We
contrast various kinds of supersolids in both continuous systems and on
lattices, both condensed matter and cold atom systems. We provide additional
new insights in studying their order parameters, symmetry breaking patterns,
the excitation spectra and detection methods.Comment: REVTEX4, 19 pages, 3 figure
Questions of perfect lenses by left handed materials
We consider questions about the much discussed "perfect lenses" made by left
handed materials. The transmission and reflection from a slab of left handed
materials are investigated and the coefficients are obtained by the standard
transfer matrix method. Possible limitations on such superlenses are explored.
It is shown that the quality of the lenses can be significantly affected by the
absorption that is necessarily present in the materials.Comment: 3 figure
Reducing alcohol use through alcohol control policies in the general population and population subgroups: a systematic review and meta-analysis.
We estimate the effects of alcohol taxation, minimum unit pricing (MUP), and restricted temporal availability on overall alcohol consumption and review their differential impact across sociodemographic groups. Web of Science, Medline, PsycInfo, Embase, and EconLit were searched on 08/12/2022 and 09/26/2022 for studies on newly introduced or changed alcohol policies published between 2000 and 2022 (Prospero registration: CRD42022339791). We combined data using random-effects meta-analyses. Risk of bias was assessed using the Newcastle-Ottawa Scale. Of 1887 reports, 36 were eligible. Doubling alcohol taxes or introducing MUP (Int$ 0.90/10 g of pure alcohol) reduced consumption by 10% (for taxation: 95% prediction intervals [PI]: -18.5%, -1.2%; for MUP: 95% PI: -28.2%, 5.8%), restricting alcohol sales by one day a week reduced consumption by 3.6% (95% PI: -7.2%, -0.1%). Substantial between-study heterogeneity contributes to high levels of uncertainty and must be considered in interpretation. Pricing policies resulted in greater consumption changes among low-income alcohol users, while results were inconclusive for other socioeconomic indicators, gender, and racial and ethnic groups. Research is needed on the differential impact of alcohol policies, particularly for groups bearing a disproportionate alcohol-attributable health burden.
Research reported in this publication was supported by the National Institute on Alcohol Abuse and Alcoholism of the National Institutes of Health under Award Number R01AA028009
Non-destructive, dynamic detectors for Bose-Einstein condensates
We propose and analyze a series of non-destructive, dynamic detectors for
Bose-Einstein condensates based on photo-detectors operating at the shot noise
limit. These detectors are compatible with real time feedback to the
condensate. The signal to noise ratio of different detection schemes are
compared subject to the constraint of minimal heating due to photon absorption
and spontaneous emission. This constraint leads to different optimal operating
points for interference-based schemes. We find the somewhat counter-intuitive
result that without the presence of a cavity, interferometry causes as much
destruction as absorption for optically thin clouds. For optically thick
clouds, cavity-free interferometry is superior to absorption, but it still
cannot be made arbitrarily non-destructive . We propose a cavity-based
measurement of atomic density which can in principle be made arbitrarily
non-destructive for a given signal to noise ratio
First-principles study of the structural energetics of PdTi and PtTi
The structural energetics of PdTi and PtTi have been studied using
first-principles density-functional theory with pseudopotentials and a
plane-wave basis. We predict that in both materials, the experimentally
reported orthorhombic phase will undergo a low-temperature phase
transition to a monoclinic ground state. Within a soft-mode framework,
we relate the structure to the cubic structure, observed at high
temperature, and the structure to via phonon modes strongly
coupled to strain. In contrast to NiTi, the structure is extremely close
to hcp. We draw on the analogy to the bcc-hcp transition to suggest likely
transition mechanisms in the present case.Comment: 8 pages 5 figure
Phase Equilibration and Magnetic Field Generation in U(1) Bubble Collisions
We present the results of lattice computations of collisions of two expanding
bubbles of true vacuum in the Abelian Higgs model with a first-order phase
transition. New time-dependent analytical solutions for the Abelian field
strength and the phase of the complex field are derived from initial conditions
inferred from linear superposition and are shown to be in excellent agreement
with the numerical solutions especially for the case where the initial phase
difference between the bubbles is small. With a step-function approximation for
the initial phase of the complex field, solutions for the Abelian field
strength and other gauge-invariant quantities are obtained in closed form.
Possible extensions of the solution to the case of the electroweak phase
transition and the generation of primordial magnetic fields are briefly
discussed.Comment: LaTeX, 41 pages, 6 figures, submitted to Physical Review
Evidence for and phases in the morphotropic phase boundary region of : A Rietveld study
We present here the results of the room temperature dielectric constant
measurements and Rietveld analysis of the powder x-ray diffraction data on
(PMN-PT) in the composition range
to show that the morphotropic phase boundary (MPB)
region contains two monoclinic phases with space groups Cm (or type) and
Pm (or type) stable in the composition ranges and
, respectively. The structure of PMN-PT in the
composition ranges 0.26, and is found to be
rhombohedral (R3m) and tetragonal (P4mm), respectively. These results are
compared with the predictions of Vanderbilt & Cohen's theory.Comment: 20 pages, 11 pdf figure
Cost-effectiveness of lung cancer screening by low-dose CT in China:a micro-simulation study
Background: The effectiveness of lung cancer screening with low-dose computed tomography (LDCT) has been established. The current study evaluates the cost-effectiveness of lung cancer screening with LDCT in a general population in China. Methods: A previously validated micro-simulation model was used to simulate a cohort of men and women on a lifetime horizon in the presence and absence of LDCT screening. The modeling data were collected from numerous national and international sources. Simulated screening scenarios included different combinations of screening intervals and start and stop ages. Additional costs (valued in Chinese Yuan, CNY; 1 USD = 6.8976 CNY, 1 EUR = 7.8755 CNY in 2020), life-years gained (LYG) and mortality reduction due to screening were also determined. The costs and life-years were discounted by 3%. All results were scaled to 1,000 individuals. The average cost-effectiveness ratio (ACER) was calculated. A willingness-to-pay threshold of CNY 217.3k / LYG was considered. A healthcare system perspective was adopted. Results: Compared to no screening, lung cancer screening by LDCT in a general Chinese population yielded 21.0 – 36.7 LYG in men and 9.2 – 16.6 LYG in women across the scenarios. For men, biennial LDCT screening yielded an ACER of CNY 171.4k – 306.3k / LYG relative to no screening. Biennial screening performed between 55 and 75 years of age was optimal at the defined threshold; it resulted in CNY 174.6k / LYG and a lung cancer mortality reduction of 9.1%, and this scenario had a 75% probability of being cost-effective. For women, the ACER ranged from CNY 364.2k to 1193.3k / LYG. Conclusions: In China, lung cancer screening with LDCT in the general population including never smokers could be cost-effective for men with 75% probability, but not for women. The optimal strategy for men would be performing biennial screening between 55 and 75 years of age
QED_3 theory of underdoped high temperature superconductors II: the quantum critical point
We study the effect of gapless quasiparticles in a d-wave superconductor on
the T=0 end point of the Kosterlitz-Thouless transition line in underdoped
high-temperature superconductors. Starting from a lattice model that has
gapless fermions coupled to 3D XY phase fluctuations of the superconducting
order parameter, we propose a continuum field theory to describe the quantum
phase transition between the d-wave superconductor and the spin-density-wave
insulator. Without fermions the theory reduces to the standard Higgs scalar
electrodynamics (HSE), which is known to have the critical point in the
inverted XY universality class. Extending the renormalization group calculation
for the HSE to include the coupling to fermions, we find that the qualitative
effect of fermions is to increase the portion of the space of coupling
constants where the transition is discontinuous. The critical exponents at the
stable fixed point vary continuously with the number of fermion fields , and
we estimate the correlation length exponent (nu = 0.65) and the vortex field
anomalous dimension(eta_Phi=-0.48) at the quantum critical point for the
physical case N=2. The stable critical point in the theory disappears for the
number of Dirac fermions N > N_c, with N_c ~ 3.4 in our approximation. We
discuss the relationship between the superconducting and the chiral (SDW)
transitions, and point to some interesting parallels between our theory and the
Thirring model.Comment: 13 pages including figures in tex
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