Time Variability Research Articles

The asymptotic preserving unified gas kinetic scheme for the multi-scale kinetic SIR epidemic model

In this paper, we present an asymptotic preserving scheme for the two-dimensional space-dependent and multi-scale kinetic SIR epidemic model which is widely used to model the spread of infectious diseases in populations. The scheme combines a discrete ordinate method for the velocity variables and finite volume method for the spatial and time variables. The idea of unified gas kinetic scheme (UGKS) is used to construct the numerical boundary fluxes which needs the formal integral solutions of the model. Due to the coupling of the three transfer equations in the SIR model, it is difficult to obtain these integral solutions dependently. We decouple the system by constructing the fluxes in a separate way. Then following the framework of UGKS we can obtain the macro auxiliary quantities which is needed in the scheme. Thus the SIR model can be solved in the sequential way. In addition, we can show numerically that the scheme is second-order accurate both in space and time. Moreover, it can not only capture the solution of the diffusion limit equations without requiring the cell size and time step being related to the smallness of the scaling parameters, but also resolve the solution in hyperbolic regime in a natural way. Furthermore, the positive property of the UGKS is analyzed in detail, and through adding time step constraint conditions and applying nodal limiters together, the positive UGKS, called PPUGKS2−order, is obtained. Moreover, in order release the time step constraints in the diffusion regime, a temporal first-order accuracy positive preserving UGKS, called PPUGKS1−order, is proposed. Finally, several numerical tests are included to validate the performance of the proposed schemes.

Mind wandering is associated with worsening attentional vigilance.

The tendency for our minds to wander is a pervasive and disruptive influence on continued task performance. Models of sustained attention have implicated mind wandering, moments when attention has turned inwards toward task-unrelated thought, in characteristic patterns of worsening performance with greater time-on-task, known as the vigilance decrement. Despite their theoretical connection, associations between mind wandering and the vigilance decrement have not been investigated systematically. Across two studies (N = 730), we evaluated covariance between within-task change in rates of probe-caught mind wandering and patterns of worsening behavioral task performance that characterize the vigilance decrement. Bivariate growth curve models characterized patterns of intraindividual linear change in mind wandering alongside concomitant changes in task accuracy, response time (RT), and RT variability. Importantly, models assessing the covariance between intraindividual change in mind wandering and behavioral outcome measures confirmed that increases in mind wandering are associated with patterns of worsening behavioral performance with greater time-on-task. In addition, we investigated the role of several moderating factors associated with patterns of within-task change: self-reported task interest and motivation, and individuals' propensity for mind wandering, and mindfulness in their daily lives. These factors moderated either the overall level or rate of within-task change in mind wandering. Our results provide support for models of sustained attention that directly implicate mind wandering in worsening behavioral performance with greater time-on-task in continuous performance tasks requiring sustained attention. (PsycInfo Database Record (c) 2024 APA, all rights reserved).

Comparison of Cognitive Functions between Healthy Controls and Individuals with Chronic Low Back Pain with High and Low Pain Catastrophizing: A Cross-sectional Study.

Researchers suggested that the interruptive effects of chronic pain on cognitive functions may be modulated by the level of pain catastrophizing (PC). However, in individuals with chronic low back pain (CLBP), domains of cognitive function that may be affected by the level of PC remain largely unclear. Therefore, this study was aimed to compare cognitive functions between healthy controls and individuals with CLBP with high and low PC. This cross-sectional study examined cognitive functions of 42 individuals with CLBP and 21 healthy controls. The PC scale was used to stratify participants with CLBP into high and low PC. Participants performed 5 cognitive tests from the Cambridge Neuropsychological Test Automated Battery, namely five-choice reaction time, rapid visual processing, spatial working memory, attention switching task, and stop signal task. The statistical analyses revealed that compared to individuals with CLBP with low PC and healthy controls, individuals with high PC demonstrated greater values of the between errors (P=0.01), reaction latency (P<0.001), and stop signal reaction time variables (P=0.004, P=0.003, respectively) but lower values of probability of hit (P=0.02, P=0.01, respectively), A' (P=0.01, P<0.001, respectively), and percent correct trials variables (P=0.002, P<0.001, respectively). The results of the current study showed deficits in sustained attention, working memory, cognitive flexibility, and inhibitory control in individuals with CLBP with high PC. From a clinical perspective, therapeutic interventions targeting PC should be considered to decrease catastrophic thinking about pain in individuals with CLBP. Additional research is warranted to explore cognitive functioning as an outcome of these interventions in individuals with CLBP.

Service center in electricity distribution sector with variable peak electricity time: A two-stage queuing model approach with nested simulation

Customer service is essential for any business, significantly impacting customer satisfaction, brand reputation, and reducing associated costs. In the electricity industry, this importance is heightened due to the critical nature of electricity in daily life and growing usage rate of new technologies. Effective customer service in electric distribution companies involves handling a wide range of inquiries, from billing issues to technical support, requiring both remote and on-site assistance. The variability in customer calls, influenced by factors such as peak electricity hours, and different service and customer types, presents unique challenges in designing efficient service centers. This research develops a tailored model for the service center operations of a power distribution company, focusing on optimal staffing levels within budget constraints. A two-stage queuing model is proposed to address the needs of residential and non-residential customers. The study employs nested simulation techniques to account for variability in customer arrival times and peak hours. Key performance indicators (KPIs) are used to evaluate the effectiveness of staffing policies, considering both quantitative and qualitative costs. The study integrates stochastic optimization and ranking and selection methods to identify the best staffing configurations. The findings offer actionable insights for improving customer service efficiency and operational effectiveness in electricity customer service centers.

Pilot deployment of a machine-learning enhanced prediction of need for hemorrhage resuscitation after trauma – the ShockMatrix pilot study

ImportanceDecision-making in trauma patients remains challenging and often results in deviation from guidelines. Machine-Learning (ML) enhanced decision-support could improve hemorrhage resuscitation.AimTo develop a ML enhanced decision support tool to predict Need for Hemorrhage Resuscitation (NHR) (part I) and test the collection of the predictor variables in real time in a smartphone app (part II).Design, setting, and participantsDevelopment of a ML model from a registry to predict NHR relying exclusively on prehospital predictors. Several models and imputation techniques were tested. Assess the feasibility to collect the predictors of the model in a customized smartphone app during prealert and generate a prediction in four level-1 trauma centers to compare the predictions to the gestalt of the trauma leader.Main outcomes and measuresPart 1: Model output was NHR defined by 1) at least one RBC transfusion in resuscitation, 2) transfusion ≥ 4 RBC within 6 h, 3) any hemorrhage control procedure within 6 h or 4) death from hemorrhage within 24 h. The performance metric was the F4-score and compared to reference scores (RED FLAG, ABC). In part 2, the model and clinician prediction were compared with Likelihood Ratios (LR).ResultsFrom 36,325 eligible patients in the registry (Nov 2010—May 2022), 28,614 were included in the model development (Part 1). Median age was 36 [25–52], median ISS 13 [5–22], 3249/28614 (11%) corresponded to the definition of NHR. A XGBoost model with nine prehospital variables generated the best predictive performance for NHR according to the F4-score with a score of 0.76 [0.73–0.78]. Over a 3-month period (Aug—Oct 2022), 139 of 391 eligible patients were included in part II (38.5%), 22/139 with NHR. Clinician satisfaction was high, no workflow disruption observed and LRs comparable between the model and the clinicians.Conclusions and relevanceThe ShockMatrix pilot study developed a simple ML-enhanced NHR prediction tool demonstrating a comparable performance to clinical reference scores and clinicians. Collecting the predictor variables in real-time on prealert was feasible and caused no workflow disruption.

Mental health trajectories among Syrian refugees in Norway: A longitudinal cohort study

Abstract Background Refugees encounter various risk factors that can affect their mental health throughout the migration process. However, while most studies focus on mental health challenges at the time of resettlement, only a few explore these changes over an extended period. This study aims to explore changes in mental health among Syrian refugees in Norway and to identify influencing factors. Methods This is a prospective cohort study using data from CHART and Integration for Health studies, which followed Syrian refugees granted settlement in Norway. Data collection took place in Lebanon between 2017-2018 (baseline), and at one- and four-years post-arrival in Norway. Assessments for anxiety/depression and post-traumatic stress disorder (PTSD) were conducted using the Hopkins Symptom Checklist (HSCL-10) and the Harvard Trauma Questionnaire, respectively. Mixed-effects logistic regression analyzed temporal changes, with results presented as odds ratio (OR) with 95% confidence intervals (CI). The study also explored the effect modification of outcomes by the following baseline factors: age, gender, education. Results A total of 132 participants were included in all three data collection points. There was a decrease in the proportion of participants reporting anxiety/depression (from 30% to 28%, OR 0.1, 95% CI 0.1 - 0.2) four years post-settlement. The proportion of participants reporting PTSD symptoms decreased one year after settlement (from 4% to 3%, OR 0.3, 95% CI 0.1 - 0.7), but increased to 4% four years after arrival, showing no improvement from baseline (OR 0.8, 95% CI 0.4 - 2.0). No interactions were observed between changes over time and baseline variables. Conclusions After four years in Norway, Syrian refugees reported improvement in anxiety/depression, but PTSD symptoms worsened. This highlights the need for ongoing support that extends beyond the initial phases of resettlement. Key messages • Refugees face various risk factors that affect their mental health throughout the migration process. • Ongoing mental health support for refugees is essential, beyond the initial resettlement phase.

Photoactivated chromophore for keratitis-Corneal cross-linking in dogs and cats: A retrospective study in Italy.

To evaluate the success and failure rate of photoactivated chromophore for keratitis-corneal cross-linking (PACK-CXL) therapy in a single population of dogs and cats. To identify the usefulness of the PACK-CXL based on ulcer depth and establish a cutoff at which this procedure could be recommended. To analyze the influence of the different variables in corneal healing time and to report the presence of secondary endothelial damage and cataract formation. Medical records of dogs and cats with presumptive infectious keratitis which underwent accelerated epithelium-off PACK-CXL between 2016 and 2023 were reviewed and analyzed. Records for 369 animals were included, and the overall success rate for healing was 97% (range 4-74 days and no rescue procedure). The second success (re-epithelialization <30 days and no rescue procedure) rate was 86%, and a total of 40 eyes needed more than 1 month for the corneal repair. Corneal ulcers were classified in three categories based on the depth: 0%-33% (46%), 34%-66% (37.4%), and 67%-100% (16.5%). The cutoff at which PACK-CXL had a higher probability of failure was with ulcer depth >66.5%. Animals who suffered from keratomalacia and hypopyon at presentation, or were treated with topical serum or gentamicin after PACK-CXL showed an increase in epithelial healing time (EHT). Increasing age, brachycephalic conformation, keratomalacia alone, and deeper ulcers were identified as risk factors for the treatment outcome. Secondary endothelial injury or cataract formation was not noted in this study. Accelerated PACK-CXL is a non-invasive, adjunctive treatment to medical therapy, which can be used in presumed infectious keratitis with a high probability of success. However, it is important to take in consideration the patient age, skull conformation, presence of keratomalacia, and the ulcer depth.

The Effect Of Air Lead (Pb) And Individual Characteristics On Subjective Complaints Of Gas Station Operators

Lead (Pb) is an air pollutant present in particulate form, often known as metallic powder. Gas station operators are one of the groups at risk of exposure to lead from motor vehicle emissions, which is harmful to health because it can accumulate in the body. This study aims to analyse the effect of airborne lead (Pb) and individual characteristics on the subjective complaints of petrol station operators in Surabaya. This study is an analytical observational study with a cross-sectional approach with a sample size of 28 respondents. Data were collected through measurements, observations and interviews, which were then processed and analysed using chi-square test. The results showed that airborne Pb measurements at two points met the NAB based on Permenaker No. 5 of 2018, which is less than 0.05 mg/m3. Based on the chi-square test, it was found that the variables of working time and the habit of using PPE had an effect on subjective complaints with a p-value &lt;0.05. The variables airborne Pb, age and smoking habits had no effect on subjective complaints.

Second law and Liu relations: the no-reversible-direction axiom—revisited

AbstractA thermodynamic process is governed by balance equations in field-formulated thermodynamics. Especially the balance equation of entropy takes a prominent role: it introduces the Second Law in the form of a dissipation inequality via the non-negative entropy production. Balance equations and dissipation inequality are independent of the considered material which is described by additional constitutive equations which need the introduction of a state space which is spanned by the state space variables. Inserting these constitutive equations into the balance equations results in the balance equations on state space which include the first order time and position derivatives of the state space variables, called “higher derivatives” wich are directional derivatives in a mathematicle sense. Why do not appear the latter in the Liu Relations which pretend to describe material as well as the equations on state space do ? The answer is that the Liu Relations describe materials whose entropy production does not depend on the higher derivatives. Consequently, the Liu Relations are more specific than the balance equations on state space. A toy example concerning heat conduction in compressible fluids is in two different versions added for elucidation.

Titanium Dioxide Nanoparticle: A Comprehensive Review on Synthesis, Applications and Toxicity

Nanotechnology has garnered significant interest worldwide due to its wide-ranging applications across various industries. Titanium dioxide nanoparticles are one type of nanoparticle that is commonly utilised in everyday use and can be synthesized by different techniques using physical, chemical and biological extracts. Green synthesis is an economical, environmentally benign and non-toxic method of synthesising nanoparticles. Titanium dioxide nanoparticles have a positive impact on plant physiology, particularly in response to biotic and abiotic stresses, depending on various factors like size, concentration, exposure of the nanoparticles and other variables. Further, titanium dioxide nanoparticles have many applications, such as being used as nano-fertilizers, adsorption of heavy metal from industrial wastewater and antimicrobial activity, as discussed in this review paper. Previous studies investigated whether titanium dioxide nanoparticles also induce genotoxicity may be due to mishandling procedure, exposure time, size, concentration and other variables. This is still contradictory and requires more research. The present review is a pragmatic approach to summarize the synthesis, application, nanotoxicity, genotoxicity and eco-friendly method of nanoparticle synthesis and disposable.

Reconstructing the Ocean State Using Argo Data and a Data-Driven Method

Abstract Over the past two decades, Argo profiles have provided unprecedented insight into the global patterns of space and time variability of ocean temperature and salinity, significantly reducing associated uncertainties. However, analyzing such assessments during the pre-Argo period remains challenging due to the scarcity of observations in many regions. From the Argo period, a set of dominant three-dimensional patterns can be estimated using Empirical Orthogonal Function (EOF) analysis, which helps to fill in observational gaps. From the associated principal components, temporal fluctuations can be observed, aiming to build a catalog of possible ocean state trajectories. To map pre-Argo observations, EOFs are used in a data assimilation framework that uses this catalog to feed an analog prediction and provide reanalysis. In this study, a new data-driven interpolation method called RedAnDA (Reduced-space Analog Data Assimilation) was tested in the tropical Pacific Ocean. RedAnDA was first validated through an Observing System Simulation Experiment (OSSE) approach, using synthetic observations extracted from a model simulation. It was subsequently applied to a real historical dataset and compared with other available reanalysis products. Overall, the reconstructed temperature field showed variability consistent with the OSSE true field and other reanalysis products in the real data application. Further improvements are needed to optimally estimate uncertainty, but RedAnDA already combines valuable information about state predictability, observational sampling, and unresolved scale issues.

Existence and uniqueness of the solution to initial and inverse problems for integro-differential heat equations with fractional load

This work is devoted to the unique solvability of the direct and inverse problems for a multidimensional heat equation with a fractional load in Holder spaces. In the problem under consideration, the loaded term is in the form of a fractional integral operator for the time variable. We prove the existence and uniqueness of the solution to these problems by the contraction mapping theorem and the theory of integral equations. For more information see https://ejde.math.txstate.edu/Volumes/2024/64/abstr.html

Broad-line Region of the Quasar PG 2130+099. II. Doubling the Size Over Four Years?

Over the past three decades, multiple reverberation mapping (RM) campaigns conducted for the quasar PG 2130+099 have exhibited inconsistent findings with time delays ranging from ∼10 to ∼200 days. To achieve a comprehensive understanding of the geometry and dynamics of the broad-line region (BLR) in PG 2130+099, we continued an ongoing high-cadence RM monitoring campaign using the Calar Alto Observatory 2.2 m optical telescope for an extra four years from 2019 to 2022. We measured the time lags of several broad emission lines (including He ii, He i, Hβ, and Fe ii) with respect to the 5100 Å continuum, and their time lags continuously vary through the years. Especially, the Hβ time lags exhibited approximately a factor of 2 increase in the last two years. Additionally, the velocity-resolved time delays of the broad Hβ emission line reveal a back-and-forth change between signs of virial motion and inflow in the BLR. The combination of negligible (∼10%) continuum change and substantial time-lag variation (over 2 times) results in a significant scatter in the intrinsic R Hβ –L 5100 relationship for PG 2130+099. Taking the consistent changes in the continuum variability time scale and the size of the BLR into account, we tentatively propose that the changes in the measurement of the BLR size may be affected by “geometric dilution”

Regional Sensorimotor Effects of Chiropractic Spinal Manipulation: Preliminary Results From an Experimental Study.

The purpose of this study was to assess the effects of different spinal manipulation (SM) techniques and target segments on a specific dermatome and myotome, when compared with a remote spinal cord segment that served as a control location. Twenty-nine healthy volunteers were randomized to receive instrumental (Activator IV, Activator Methods International Ltd) or manual SM at the C6, C1, and T4 vertebral segments in 3 independent sessions. Pressure pain thresholds (PPTs) and muscle strength were examined at the C6 (test) and L4 (control) dermatomes and myotomes, at baseline and after intervention. Linear mixed-effects models were used to analyze changes over time and interindividual variability. Pressure pain thresholds significantly increased at both proximal and distal C6 dermatome locations (P < .05), irrespective of the technique and segment of application (P > .2). No significant changes were observed at the L4 dermatome. Muscle strength remained unchanged throughout the study. Multilevel modeling revealed significant associations between increased PPTs along the C6 dermatome (P < .001), whereas the combination of technique and target segment predicted PPT increases at the proximal C6 dermatome. These findings support regional, rather than segmental mechanisms underlying the sensory effects of SM. Specifically, significant increases in PPTs along the C6 dermatome suggest localized effects on pain sensitivity, which may depend on the target spinal region. Further investigation is needed to better understand these regional changes of SM and their potential clinical implications.

From ‘dankgevingsdag' to 'turkey party’: Historical sociolinguistic perspectives on loan strategies in Flemish-American heritage newspapers

Within the domain of historical sociolinguistics, attention for heritage languages has been on the rise in the last decade (see e.g., Brown 2019; Litty 2019). The goal of this paper is to contribute to that growing body of research studying the role of sociolinguistic factors in heritage language use in the past, by looking at the lexical output of Belgian emigrants in the United States using heritage newspapers. We will investigate the borrowing patterns in three Flemish-American newspapers that were published in the 19th and 20th centuries and circulated widely within the Flemish-American communities. We focus on (1) borrowing rate (how many English-origin lexemes are transferred?), and (2) borrowing type (which loan processes are involved?). The findings are interpreted in terms of the social variables time and space to chart diachronic as well as regional differences, besides looking at differences between the newspapers more generally.

Optimization of wood vinegar from cacao pod shells by response surface methodology

The purpose of this study is to find the optimal conditions for producing wood vinegar from cacao pod shells using Response Surface Methodology (RSM). Box Behnken Design (BBD) was used to optimize the variables of pyrolysis times, temperature, and particle size. Wood vinegar was prepared by slow pyrolysis technology. The RSM with three design variables including pyrolysis duration at 50, 75, and 100 minutes; pyrolysis temperatures at 300°C, 340°C, and 380°C; and particle size of 3, 5 and 7 cm with 15 runs were applied. Chemical characterization of wood vinegar was performed by Gas Chromatography-Mass Spectrometry (GC-MS) analysis. The results showed that phenolic, furan, and ketone compounds were the main component in the cacao pod shells vinegar. The optimum production of wood vinegar from cacao pod shells based on RSM results was identified at a pyrolysis time of 100 minutes, a temperature of 353°C, and a particle size of 3 cm.

Cognitive functions explain discrete parameters of normal walking and dual-task walking, but not postural sway in quiet stance among physically active older people.

Postural control is dependent on the central nervous system's accurate interpretation of sensory information to formulate and execute adequate motor actions. Research has shown that cognitive functions are associated with both postural control and fall risk, but specific associations are not established. The aim of this study was to explore how specific components of everyday postural control tasks are associated with both general and specific cognitive functions. Forty-six community-dwelling older adults reported their age, sex, physical activity level, falls and fall-related concerns. The following cognitive aspects were assessed: global cognition, executive functions, processing speed and intraindividual variability. Postural control was quantified by measuring postural sway in quiet stance, walking at a self-selected pace, and walking while performing a concurrent arithmetical task. Separate orthogonal projections of latent structures models were generated for each postural control outcome using descriptive and cognitive variables as explanatory variables. Longer step length and faster gait speed were related to faster processing speed and less intraindividual variability in the choice reaction test. Moreover, longer step length was also related to less fall-related concerns and less severe fall-related injuries, while faster gait speed was also related to female sex and poorer global cognition. Lower dual-task cost for gait speed was explained by the executive function inhibition and faster processing speed. Postural sway in quiet stance was not explained by cognitive functions. Cognitive functions explained gait speed and step length during normal walking, as well as the decrease of gait speed while performing a concurrent cognitive task. The results suggest that different cognitive processes are important for different postural control aspects. Postural sway in quiet stance, step time and gait variability seem to depend more on physical and automatic processes rather than higher cognitive functions among physically active older people. The relationships between cognitive functions and postural control likely vary depending on the specific tasks and the characteristics of different populations.

Early prehospital mechanical cardiopulmonary resuscitation use for out-of-hospital cardiac arrest: an observational study

BackgroundThe use of mechanical cardiopulmonary resuscitation device has been very prevalent in out-of-hospital cardiac arrest rescue. This study aimed to investigate whether the timing of mechanical cardiopulmonary resuscitation device set-up correlated with the the outcome of cardiac arrest patients.MethodsWe retrospectively reviewed adult nontrauma cardiac arrest cases in New Taipei City, Taiwan, from January to December 2022. Demographic data, intervention-related factors, and the time variables of mechanical cardiopulmonary resuscitation were collected. The outcomes included the return of spontaneous circulation and 24-hour survival. We compared patients who achieved spontaneous circulation and those who did not with univariate and multivariable regression analyses.ResultsIn total, 1680 patients who received mechanical cardiopulmonary resuscitation were included in the analysis. Reducing the time interval from manual chest compression initiation to device setup was independently associated with the return of spontaneous circulation and 24-hour survival, especially in the subgroup of patients of initial shockable rhythm. Receiver operating characteristic analysis revealed that the outcome of patients with an initial shockable rhythm could be predicted by the mechanical cardiopulmonary resuscitation setup time, with areas under the curve of 60.8% and 63.9% for ROSC and 24-hour survival, respectively. The cutoff point was 395.5 s for patients with an initial shockable rhythm.ConclusionA positive correlation was found between early mechanical cardiopulmonary resuscitation intervention and the outcomes of out-of-hospital cardiac arrest patients. The time between manual chest compression and device setup could predict the return of spontaneous circulation and 24-hour survival in the subgroup of patients with initially shockable rhythm with the optimal cutoff point at 395.5 s.

Reaching and stepping respond differently to medication and cueing in Parkinson’s disease

The basal ganglia contribute to internal timekeeping, and dopaminergic medication has been observed to moderate timing deficits associated with Parkinson’s Disease (PD) during single joint movements. However, it is unclear whether similar effects can be observed in multi-joint movements. Twenty-five people with PD and twelve healthy peers performed repetitive reaching and stepping-in-place tasks with and without auditory cues at their self-selected maximal cadence. The PD group was measured ON and OFF medication. Reduced cadence error was found for both groups and tasks when cued, and ON PD exhibited decreased cadence compared to OFF PD. Overall timing variability was no different from controls, but differences were found in estimates of clock and motor variance using the Wing-Kristofferson model of interval timing. A medication and cueing interaction during the reaching task produced increased clock variance in uncued, ON PD. During the stepping task, clock and motor variance of the PD group were unaffected by cues, in contrast to the control group. Serial lag-one correlation was reduced in both groups for cued reaching, but was unaffected by cueing or medication in the PD group when stepping-in-place. These findings suggest that overall timing variability may not capture timing deficits in PD.

Direct observation of the neural computations underlying a single decision

Neurobiological investigations of perceptual decision-making have furnished the first glimpse of a flexible cognitive process at the level of single neurons. Neurons in the parietal and prefrontal cortex are thought to represent the accumulation of noisy evidence, acquired over time, leading to a decision. Neural recordings averaged over many decisions have provided support for the deterministic rise in activity to a termination bound. Critically, it is the unobserved stochastic component that is thought to confer variability in both choice and decision time. Here, we elucidate this drift-diffusion signal on individual decisions. We recorded simultaneously from hundreds of neurons in the lateral intraparietal cortex of monkeys while they made decisions about the direction of random dot motion. We show that a single scalar quantity, derived from the weighted sum of the population activity, represents a combination of deterministic drift and stochastic diffusion. Moreover, we provide direct support for the hypothesis that this drift-diffusion signal approximates the quantity responsible for the variability in choice and reaction times. The population-derived signals rely on a small subset of neurons with response fields that overlap the choice targets. These neurons represent the integral of noisy evidence. Another subset of direction-selective neurons with response fields that overlap the motion stimulus appear to represent the integrand. This parsimonious architecture would escape detection by state-space analyses, absent a clear hypothesis.