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M. B. Weissman

Publications and source records attributed to M. B. Weissman.

18 recordsLinked to original sources
arXiv2024

Proximity Ascertainment Bias in Early Covid Case Locations

A comparison of the distances to the Huanan Seafood Market of early Covid cases with known links to the market versus cases without known links shows results apparently incompatible with a location model lacking proximity ascertainment bias. The sign of the difference instead agrees with a model in which such ascertainment bias is large. In the presence of such bias inferences based on the clustering of case locations become unreliable.

physics.soc-ph↗
arXiv2023

Comment on "Examining the effect of counter-narratives about physics on women's physics career intentions"

A paper evaluating the effects of lessons intended to encourage high school students to continue physics studies made some important errors. One was to underestimate the width of confidence intervals by failing to use standard cluster randomization analysis. Another was to use a missing-data imputation program that inappropriately assumes that data are missing at random, leading to potential bias in estimating the effect. The last was to omit discussion of how the treatment used was likely to produce substantial social desirability survey response bias, eroding external validity.

physics.ed-ph↗
arXiv2022

Methods of Causal Inference in Physics Education Research

Finding good educational policies requires sound estimates of their potential effects. Methods for making such estimates, i.e. finding causal estimands, have made great progress in the last few decades. Nevertheless, serious errors in causal reasoning have been found previously in papers n a leading physics education journal, Physical Review Physics Education Research. Here we examine three more recent papers from that journal that present explicit methods of causal inference. The methods given include major errors, including in identifying causal mediation, choosing variables to control for, and imputing missing data.

physics.ed-ph↗
arXiv2021

On Policy Recommendations from Causal Inference in Physics Education Research

Sound educational policy recommendations require valid estimates of causal effects, but observational studies in physics education research sometimes have loosely specified causal hypotheses. The connections between the observational data and the explicit or implicit causal conclusions are sometimes misstated. The link between the causal conclusions reached and the policy recommendations made is also sometimes loose. Causal graphs are used to illustrate these issues in several papers from Physical Review Physics Education Research. For example, the core causal conclusion of one paper rests entirely on the choice of a causal direction although an unstated plausible alternative gives an exactly equal fit to the data.

physics.ed-ph↗
arXiv2019

Multiple Aging Mechanisms in Ferroelectric Deuterated Potassium Dihydrogen Phosphate

The anomalously large dielectric aging in ferroelectric partially deuterated potassium dihydrogen phosphate (DKDP) is found to have multiple distinct mechanisms. Two components cause decreases in dielectric response over a limited range of fields around the aging field. A large fraction of this aging occurs on time scales of ~1000s after a field change, as expected for a hydrogen/deuterium diffusion mechanism. A slower component can give almost complete loss of domain-wall dielectric response at the aging field after weeks of aging. There is also a particularly unusual aging in which the dielectric response increases with time after rapid cooling.

cond-mat.mtrl-sci↗
arXiv2018

Non-equilibrium Strain Relaxation Noise in the Relaxor Ferroelectric (PbMg1/3Nb2/3O3)100-x( PbTiO3)x

Large low-frequency noise is found in some perovskite relaxor ferreoelectrics when they are polarized, regardless of whether the polarization is accompanied by an applied electric field. The noise appears both in the ferroelectric and relaxor states, including in the nominally ergodic paraelectric state at temperatures above the susceptibility peak. Since it is present whenever the samples are microphonic due to piezoelectricity but not evident when they are not microphonic, it appears to be a response to mechanical strain changes. Dependence of the noise on sample thermal history indicates that non-equilibrium strain relaxation is the source, even in the temperature range for which the sample is nominally ergodic. Non-equilibrium noise in the absence of net piezoelectricity is found at somewhat higher frequencies.

cond-mat.mtrl-sci↗
arXiv2017

Aging Dynamics in Ferroelectric Deuterated Potassium Dihydrogen Phosphate

Anomalously large dielectric aging is found in the high-susceptibility plateau ferroelectric regime of ~95% deuterated potassium dihydrogen phosphate (DKDP). Much less aging is found in non-deuterated KDP. Optical images of the DKDP domain structure show no dramatic change during aging. Small changes in electric field restore the pre-aged susceptibility, but the previous aging almost recovers after returning to the aging field. Susceptibility vs. field can show memory of at least two prior aging fields. Rectifying non-linear susceptibility develops for fields slightly above or below a prior aging field. Aging effects are not fully erased even by brief heating above the Curie point, indicating a role for diffusion of hydrogen to the domain walls, leaving changes in disorder that can survive temporary absence of domain walls. Abrupt random-sign steps in polarization on cooling are accompanied by increases in susceptibility, indicating competition between large-scale domain-wall interaction effects and effects of local interactions with disorder.

cond-mat.mtrl-sci↗
arXiv2017

Barkhausen Noise Probe of the Ferroelectric Transition in the Relaxor PbMg1/3Nb2/3O3-12% PbTiO3

Barkhausen current noise is used to probe the slow field-driven conversion of the glassy relaxor ferroelectric state to an ordered ferroelectric (FE) state. The frequent presence of distinct micron-scale Barkhausen events well before the polarization current starts to speed up shows that the process is not a conventional nucleation-limited one. The prevalence of reverse switching events near the onset of the rapid part of the transition strongly indicates that electric dipole interactions play a key role. The combination of Barkhausen noise changes and changes in the complex dielectric response indicate that the process consists of an initial mixed-alignment domain formation stage followed by growth of the domains aligned with the applied field.

cond-mat.mtrl-sci↗
arXiv2010

Anomalous Noise in the Pseudogap Regime of YBa$_2$Cu$_3$O$_{7-δ}$

An unusual noise component is found near and below about 250 K in the normal state of underdoped YBCO and Ca-YBCO films. This noise regime, unlike the more typical noise above 250 K, has features expected for a symmetry-breaking collective electronic state. These include large individual fluctuators, a magnetic sensitivity, and aging effects. A possible interpretation in terms of fluctuating charge nematic order is presented.

cond-mat.supr-con↗
arXiv2007

Stability of Glassy and Ferroelectric States in the Relaxors PbMg1/3Nb2/3O3 and PbMg1/3Nb2/3O3-12% PbTiO3

The stability of the disordered glassy phase in the relaxors PbMg1/3Nb2/3O3 and (PbMg1/3Nb2/3O3)0.88(PbTiO3)0.12, called PMN and PMN-PT, was investigated by preparing partially polarized samples and allowing them to age at zero field in the temperature range for which the phase is history-dependent. The PMN-PT polarization would spontaneously increase until long-range order formed, first appearing as giant polarization noise. Thus the thermodynamically stable phase in PMN-PT appears to be ferroelectric. In contrast, a PMN sample lacking the sharp first-order field-driven transition found in some other samples spontaneously depolarized, consistent with its glassy state being thermodynamically stable. Detailed thermal depolarization results in PMN show two distinct broad peaks as well as a small fraction of material with a distribution of abrupt melting transitions.

cond-mat.mtrl-sci↗
arXiv2006

Irreversibility in Collapse-Free Quantum Dynamics and the Second Law of Thermodynamics

Proposals to solve the problems of quantum measurement via non-linear CPT-violating modifications of quantum dynamics are argued to provide a possible fundamental explanation for the irreversibility of statistical mechanics as well. The argument is expressed in terms of collapse-free accounts. The reverse picture, in which statistical irreversibility generates quantum irreversibility, is argued to be less satisfactory because it leaves the Born probability rule unexplained.

quant-ph↗
arXiv2006

Aging in the Relaxor Ferroelectric PMN/PT

The relaxor ferroelectric (PbMn$_{1/3}$Nb$_{2/3}$O$_3$)$_{1-x}$(PbTiO$_3$)$_{x}$, $x=0.1$, (PMN/PT(90/10)) is found to exhibit several regimes of complicated aging behavior. Just below the susceptibility peak there is a regime exhibiting rejuvenation but little memory. At lower temperature, there is a regime with mainly cumulative aging, expected for simple domain-growth. At still lower temperature, there is a regime with both rejuvenation and memory, reminiscent of spin glasses. PMN/PT (88/12) is also found to exhibit some of these aging regimes. This qualitative aging behavior is reminiscent of that seen in reentrant ferromagnets, which exhibit a crossover from a domain-growth ferromagnetic regime into a reentrant spin glass regime at lower temperatures. These striking parallels suggest a picture of competition in PMN/PT (90/10) between ferroelectric correlations formed in the domain-growth regime with glassy correlations formed in the spin glass regime. PMN/PT (90/10) is also found to exhibit frequency-aging time scaling of the time-dependent part of the out-of-phase susceptibility for temperatures 260 K and below. The stability of aging effects to thermal cycles and field perturbations is also reported.

cond-mat.mtrl-sci↗
arXiv2005

Two-step phase changes in cubic relaxor ferroelectrics

The field-driven conversion between the zero-field-cooled frozen relaxor state and a ferroelectric state of several cubic relaxors is found to occur in at least two distinct steps, after a period of creep, as a function of time. The relaxation of this state back to a relaxor state under warming in zero field also occurs via two or more sharp steps, in contrast to a one-step relaxation of the ferroelectric state formed by field-cooling. An intermediate state can be trapped by interrupting the polarization. Giant pyroelectric noise appears in some of the non-equilibrium regimes. It is suggested that two coupled types of order, one ferroelectric and the other glassy, may be required to account for these data.

cond-mat.mtrl-sci↗
arXiv2005

Higher Order Spectra in Avalanche Models

Utilizing the Haar transform, we study the higher order spectral properties of mean field avalanche models, whose avalanche dynamics are described by Poisson statistics at a critical point or critical depinning transition. The Haar transform allows us to obtain a time series of noise powers, $H(f_1,t)$, that gives improved time resolution over the Fourier transform. Using $H(f_1,t)$ we analytically calculate the Haar power spectrum, the real 1.5 spectra, the second spectra, and the real cross second spectra in mean field avalanche models. We verify our theoretical results with the numerical results from a simulation of the T=0 mean field nonequilibrium random field Ising model (RFIM). We also extend our higher order spectra calculation to data obtained from a numerical simulation of the T=0 infinite range RFIM for $d=3$, and experimental data obtained from an amorphous alloy, $Fe_{21}Co_{64}B_{15}$. We compare the results and obtain novel exponents.

cond-mat.stat-mech↗
arXiv2004

Electronic Transport in Underdoped YBCO Nanowires: Possible Observation of Stripe Domains

We have measured the transport properties of a series of underdoped YBa2Cu3O7 nanowires fabricated with widths of 100-250 nm. We observe large telegraph-like fluctuations in the resistance between the pseudogap temperature T* and the superconducting transition temperature Tc, consistent with the formation and dynamics of a domain structure such as that created by charge stripes. We also find anomalous hysteretic steps in the current-voltage characteristics well below Tc.

cond-mat.supr-con↗
arXiv2001

Barkhausen Noise in a Relaxor Ferroelectric

Barkhausen noise, including both periodic and aperiodic components, is found in and near the relaxor regime of a familiar relaxor ferroelectric, PbMg$_{1/3}$Nb$_{2/3}$O$_3$, driven by a periodic electric field. The temperature dependences of both the amplitude and spectral form show that the size of the coherent dipole moment changes shrink as the relaxor regime is entered, contrary to expectations based on some simple models.

cond-mat.mtrl-sci↗
arXiv1999

Emergent measure-dependent probabilities from modified quantum dynamics without state-vector reduction

Counting outcomes is the obvious algorithm for generating probabilities in quantum mechanics without state-vector reduction (i.e. many-worlds). This procedure has usually been rejected because for purely linear dynamics it gives results in disagreement with experiment. Here it is shown that if non-linear decoherence effects (previously proposed by other authors) are combined with an exponential time dependence of the scale for the non-linear effects, the correct measure-dependent probabilities can emerge via outcome counting, without the addition of any stochastic fields or metaphysical hypotheses.

quant-ph↗