Boosting Monte Carlo simulations of spin glasses using autoregressive neural networks

The autoregressive neural networks are emerging as a powerful computational tool to solve relevant problems in classical and quantum mechanics. One of their appealing functionalities is that, after they have learned a probability distribution from a dataset, they allow exact and efficient sampling of typical system configurations. Here we employ a neural autoregressive distribution estimator (NADE) to boost Markov chain Monte Carlo (MCMC) simulations of a paradigmatic classical model of spin-glass theory, namely the two-dimensional Edwards-Anderson Hamiltonian. We show that a NADE can be trained to accurately mimic the Boltzmann distribution using unsupervised learning from system configurations generated using standard MCMC algorithms. The trained NADE is then employed as smart proposal distribution for the Metropolis-Hastings algorithm. This allows us to perform efficient MCMC simulations, which provide unbiased results even if the expectation value corresponding to the probability distribution learned by the NADE is not exact. Notably, we implement a sequential tempering procedure, whereby a NADE trained at a higher temperature is iteratively employed as proposal distribution in a MCMC simulation run at a slightly lower temperature. This allows one to efficiently simulate the spin-glass model even in the low-temperature regime, avoiding the divergent correlation times that plague MCMC simulations driven by local-update algorithms. Furthermore, we show that the NADE-driven simulations quickly sample ground-state configurations, paving the way to their future utilization to tackle binary optimization problems.Comment: 13 pages, 14 figure

Scaling properties of velocity and temperature spectra above the surface friction layer in a convective atmospheric boundary layer

International audienceWe report velocity and temperature spectra measured at nine levels from 1.42 meters up to 25.7 m over a smooth playa in Western Utah. Data are from highly convective conditions when the magnitude of the Obukhov length (our proxy for the depth of the surface friction layer) was less than 2 m. Our results are somewhat similar to the results reported from the Minnesota experiment of Kaimal et al. (1976), but show significant differences in detail. Our velocity spectra show no evidence of buoyant production of kinetic energy at at the scale of the thermal structures. We interpret our velocity spectra to be the result of outer eddies interacting with the ground, not "local free convection". We observe that velocity spectra represent the spectral distribution of the kinetic energy of the turbulence, so we use energy scales based on total turbulence energy in the convective boundary layer (CBL) to collapse our spectra. For the horizontal velocity spectra this scale is (zi ?o)2/3, where zi is inversion height and ?o is the dissipation rate in the bulk CBL. This scale functionally replaces the Deardorff convective velocity scale. Vertical motions are blocked by the ground, so the outer eddies most effective in creating vertical motions come from the inertial subrange of the outer turbulence. We deduce that the appropriate scale for the peak region of the vertical velocity spectra is (z ?o)2/3 where z is height above ground. Deviations from perfect spectral collapse under these scalings at large and small wavenumbers are explained in terms of the energy transport and the eddy structures of the flow. We find that the peaks of the temperature spectra collapse when wavenumbers are scaled using (z1/2 zi1/2). That is, the lengths of the thermal structures depend on both the lengths of the transporting eddies, ~9z, and the progressive aggregation of the plumes with height into the larger-scale structures of the CBL. This aggregation depends, in top-down fashion, on zi. The whole system is therefore highly organized, with even the smallest structures conforming to the overall requirements of the whole flow

An Economic Geography Of Venture Capital Investment In Canada

This dissertation investigates the supply and demand components of Canadian venture capital investment. Four areas are addressed: (1) where venture capital firms and their investments are located, (2) investment specialization of firms in different urban markets, (3) the spatial pattern of portfolio firm industrial sector and funding stage characteristics and (4) the economic impact of portfolio firms. These investigations are based on data gathered from industrial directories, surveys of both venture capitalists and their investments, and an online database of export oriented firms.;Venture capital investors are highly concentrated and regionally biased in their portfolio selections. Further, investors located in particular urban markets specialize in certain geographic regions, funding stages and industrial sectors. The resulting spatial patterns are the aggregate result of efforts to minimize uncertainty and reduce the inherent risk of ventures. Investigation of the performance and economic impacts of venture backed firms showed that venture capitalists usually invest in the elite of small and medium sized companies. These firms typically have above average rates of growth, and strong financial positions. They commit relatively large amounts of capital to research and development activity, and are highly export oriented. As a result of their rapid growth, they generate many new employment opportunities

Inexperienced decision-makers' use of positive heuristics for marketing decisions

Purpose: Research has reliably demonstrated that decision-makers, especially expert ones, use heuristics to make decisions under uncertainty. However, whether decision-makers with little or no experience also do, and if so, how? is unknown. This research addresses this issue in the marketing context by studying how a group of young and generally inexperienced entrepreneurs decide when asked to set a price and choose a distribution channel in a scenario involving a hypothetical firm. Design/methodology/approach: The authors used think-aloud protocols to elicit data and then used inductive procedures to code the data for analysis. Findings: The inexperienced entrepreneurs in the sample used three types of heuristics in their decision-making, forming a structured process that narrows in scope. First, metacognitive heuristics, which specify a decision-making approach, were used, followed by heuristics representing the criteria they considered, and finally, heuristics detailing the execution of a selected option. The authors also found that heuristics relating to a market orientation, especially customer-centric criteria, were the most common, but these were balanced with ones representing an internal orientation or growth. Research limitations/implications: The generally inexperienced decision-makers the authors’ studied used heuristics in a structured way that helped them to select and balance several potentially conflicting decision-making criteria. As with most research using qualitative research designs, the generalizability of these findings is unclear. Further research on the mechanisms by which relatively inexperienced decision-makers learn the heuristics they use is recommended. Originality/value: This research's novelty lies in its focus on heuristic use by nonexpert decision-makers under conditions of uncertainty and the findings about their scope and the order they are used. As the authors collected data from think-aloud protocols with relatively young entrepreneurs with limited experience, they also offer a description of the heuristics used by nascent entrepreneurs when making marketing decisions about pricing and channels. The most surprising conclusion is that even without relevant domain-specific knowledge, decision-makers can use heuristics in an ecologically rational way (i.e. structured to match the environment).Peer reviewe

On the Sets of Real Numbers Recognized by Finite Automata in Multiple Bases

This article studies the expressive power of finite automata recognizing sets of real numbers encoded in positional notation. We consider Muller automata as well as the restricted class of weak deterministic automata, used as symbolic set representations in actual applications. In previous work, it has been established that the sets of numbers that are recognizable by weak deterministic automata in two bases that do not share the same set of prime factors are exactly those that are definable in the first order additive theory of real and integer numbers. This result extends Cobham's theorem, which characterizes the sets of integer numbers that are recognizable by finite automata in multiple bases. In this article, we first generalize this result to multiplicatively independent bases, which brings it closer to the original statement of Cobham's theorem. Then, we study the sets of reals recognizable by Muller automata in two bases. We show with a counterexample that, in this setting, Cobham's theorem does not generalize to multiplicatively independent bases. Finally, we prove that the sets of reals that are recognizable by Muller automata in two bases that do not share the same set of prime factors are exactly those definable in the first order additive theory of real and integer numbers. These sets are thus also recognizable by weak deterministic automata. This result leads to a precise characterization of the sets of real numbers that are recognizable in multiple bases, and provides a theoretical justification to the use of weak automata as symbolic representations of sets.Comment: 17 page

The Validity of a Novel Staged Exercise Test for Measuring Lactate Metabolism and Performance in Cyclists

Several types of lactate threshold (Tlac) protocols have been developed over the years to maximize accuracy and reliability while maintaining ease of measurement and application to training and performance. PURPOSE: The purpose of this study was to determine the validity of a novel staged maximal lactate steady state exercise test (sMLSS) in predicting the MLSS using the Lactate Plus® (Nova Biomedical, Waltham, MA) analyzer. METHODS: Blood lactate concentration (BLC) was measured in duplicate for all tests. Seven trained cyclists (20 miles per week) performed a V̇O2max test starting at 100W and increasing by 30W every three minutes until volitional fatigue. Lactate threshold was defined as the previous workload to a 2 mmol•L-1 increase in BLC. Next, the sMLSS test was performed starting at the Tlac workload, determined previously, then increasing 10W every 15 minutes for a total of three stages. BLC was measured every 3 minutes. MLSS was predicted by visual inspection and defined as \u3c 1.0 mmol•L-1 increase in the final 6 minutes of the stage. Finally, cyclists then performed two to six MLSS exercise tests, adjusting by 5W depending on lactate response, to validate the sMLSS. MLSS was determined at the maximal workload with \u3c 1 mmol•L-1 increase in BLC in the final 20 minutes. Dependent T-test and Pearson correlation coefficient was used to determine reliability between lactate trials. Bland-Altman plots, One-way ANOVA, and regression analyses were used to analyze differences between the types of exercise tests. RESULTS: There were no significant differences for duplicate BLC trials for all tests (p= 0.21; r=0.982). The sMLSS was significantly correlated with the MLSS workload and percentage of max workload (r = 0.997; p=0.001, r = 0.978, p=0.01), respectively. There was no bias noted between sMLSS and MLSS protocols for predicting lactate accumulation. CONCLUSION: This novel protocol was determined to be a valid and efficient means determining lactate performance in recreationally trained cyclists. The sMLSS was effective at reducing testing time from 12 days to 3 days

The DDO IVC Distance Project: Survey Description and the Distance to G139.6+47.6

We present a detailed analysis of the distance determination for one intermediate Velocity Cloud (IVC G139.6+47.6) from the ongoing DDO IVC Distance Project. Stars along the line of sight to G139.6+47.6 are examined for the presence of sodium absorption attributable to the cloud, and the distance bracket is established by astrometric and spectroscopic parallax measurements of demonstrated foreground and background stars. We detail our strategy regarding target selection, observational setup, and analysis of the data, including a discussion of wavelength calibration and sky subtraction uncertainties. We find a distance estimate of 129 (+/- 10) pc for the lower limit and 257 (+211-33) pc for the upper limit. Given the high number of stars showing absorption due to this IVC, we also discuss the small-scale covering factor of the cloud and the likely significance of non-detections for subsequent observations of this and other similar IVC's. Distance measurements of the remaining targets in the DDO IVC project will be detailed in a companion paper.Comment: 10 pages, 6 figures, LaTe

Biomass burning and pollution aerosol over North America: Organic components and their influence on spectral optical properties and humidification response

Thermal analysis of aerosol size distributions provided size resolved volatility up to temperatures of 400°C during extensive flights over North America (NA) for the INTEX/ICARTT experiment in summer 2004. Biomass burning and pollution plumes identified from trace gas measurements were evaluated for their aerosol physiochemical and optical signatures. Measurements of soluble ionic mass and refractory black carbon (BC) mass, inferred from light absorption, were combined with volatility to identify organic carbon at 400°C (VolatileOC) and the residual or refractory organic carbon, RefractoryOC. This approach characterized distinct constituent mass fractions present in biomass burning and pollution plumes every 5–10 min. Biomass burning, pollution and dust aerosol could be stratified by their combined spectral scattering and absorption properties. The “nonplume” regional aerosol exhibited properties dominated by pollution characteristics near the surface and biomass burning aloft. VolatileOC included most water-soluble organic carbon. RefractoryOC dominated enhanced shortwave absorption in plumes from Alaskan and Canadian forest fires. The mass absorption efficiency of this RefractoryOC was about 0.63 m2 g−1 at 470 nm and 0.09 m2 g−1 at 530 nm. Concurrent measurements of the humidity dependence of scattering, γ, revealed the OC component to be only weakly hygroscopic resulting in a general decrease in γ with increasing OC mass fractions. Under ambient humidity conditions, the systematic relations between physiochemical properties and γ lead to a well-constrained dependency on the absorption per unit dry mass for these plume types that may be used to challenge remotely sensed and modeled optical properties

Gender & Sport Related Differences in Electrocardiogram & Pre-participation Exams (PPE) in College Age Athletes

TACSM Abstract Gender & sport related differences in electrocardiogram & pre-participation exams (PPE) in college age athletes Harp J, Garcia B, Fulfer S, Cvikel J ,. Blevins-McNaughton J. Clinical Exercise Research Facility; Kinesiology; Tarleton State University; Stephenville, TX Category: Masters Advisor/ Mentor: Blevins-McNaughton, JS ([email protected]) ABSTRACT Background and Purpose: The NCAA requires all college level athletes receive a pre-participation physical exam. However, the pre-participation exams occasionally do not require electrocardiogram screening to help detect cardiac abnormalities. Though electrocardiograms may not be available at all testing’s, using specific markers and finding differences between gender and sport abnormalities could help detect cardiac abnormalities. The purpose of this study was to determine if there were significant differences in resting 12-Lead ECG markers in a group NCAA Div. II collegiate level athletes. Methods: Three hundred and eight college level athlete’s ages 18 to 25 participated in this study. Age, gender, height, weight, BMI, blood pressure and heart rate were measured during a pre-participation exam. Electrocardiogram measurements were gathered by using Mortara X-Scribe™ , Vacumed Turbo Fit 5™, Welch Allyn CardioPerfect™. Twelve-Lead ECGs were categorized by sport and analyzed by the lab director and the attending physician. One-way ANOVA was used to analyze differences in ECG findings in genders and sports. Independent t-test and linear regression were used to analyze differences between male and female outcomes. Significance was set at the 0.05 level. Results: No significant differences in wave conformation or arrhythmias were found between sports. Cross country athletes had significantly lower resting heart rate (61 ± 12.5 bpm) than football (70.6 ± 14 bpm), baseball (72.6 ± 12.8 bpm), track and field (73.2 ± 13.4 bpm), and cheerleading (75 ± 11.8 bpm) (P=0.003) . Resting systolic blood pressure was significantly higher in football (124.8 ± 10.4 mmHg) and baseball (124 ± 10.4 mmHg) than softball (115.8 ± 5.4 mmHg), track and field (119.2 ± 10.9 mmHg), cross country (112.7 ± 11.2 mmHg), and cheerleading (114.9 ± 7.9 mmHg) (P=0.001). Similarly, heart work expressed as rate pressure product (RPP) was significantly lower in cross country compared to all other sports. Relative to ECG parameters cross country athletes showed ECG changes typical for cardiovascular endurance training compared to all other sports including sinus bradycardia, increased RR interval, and leftward axis shift. Discussion: Although marked differences in 12-lead ECG parameters were not found between sports in this sample, two athletes were sent for further echo evaluation due to abnormal ECGs, but were subsequently cleared to participate in their sport