Intensity Trajectories Research Articles

End-of-life (EOL) trajectories among older adults dying with lung cancer (LC).

e24008 Background: Medicare decedents often receive intensive care during the last month (mth) of life. There is little information on longer (6-mth) EOL trajectories of care intensity. Area hospice use rates may reflect supply and/or patient and physician preferences, and may influence patterns for individual decedents. Methods: Using SEER-Medicare linked registry and claims data, we selected decedents diagnosed with LC between 2008-2013 who survived ≥6-mths and died between 2008-2014. We linked Dartmouth Atlas data on hospital referral region (HRR) % cancer decedents with hospice use. Each mth we assessed claims to identify cancer-directed (CD) care (chemotherapy or radiation) and pharmacologic or other palliative care services (PCS) and assigned decedents to either CD only, PCS only, concurrent CD & PCS, full-mth inpatient (IP) or full-mth hospice. We ordered monthly care intensity from high to low (IP > CD only > concurrent CD & PCS > PCS only > hospice). Using the indicators arrayed by calendar mth, we assigned each decedent to 1 of 6 trajectories: stable (6-mth continuous) hospice, stable PCS only, stable CD only or concurrent CD & PCS, decreasing intensity, increasing intensity, and mixed (multiple directional shifts). Multinomial logistic regression estimated associations between area hospice rates, socio-demographics, and comorbidity with EOL trajectory, controlling for 1st line therapy, and diagnosis stage. Results: Our sample (N = 24,342) was predominantly male (53.7%), age ≥75 years (59.4%), and non-Hispanic white (80.5%); 19.1% lived in HRRs where ≤50% of cancer decedents received any hospice care. Trajectories were 7% stable hospice, 26% stable PCS only, 4% stable CD; 29% decreasing intensity, 9% increasing intensity, and 26% mixed. Relative to stable hospice, higher HRR-level hospice rates were associated with decreasing EOL intensity; higher age, female, and married were associated with increased probability of stable hospice enrollment); Black, non-Hispanic decedents had higher risk of increasing intensity (aRRR: 1.39, 95% confidence interval: 1.09-1.76, p < .01) and mixed patterns. Conclusions: Among older decedents with LC, only 62% had 6-mth EOL trajectories indicating low- (stable hospice or PCS only) or decreasing intensity, but few received persistent CD care. Area hospice use patterns, demographic characteristics and health status were associated with EOL trajectory. Additional research is needed to identify subgroups at risk of high or increasing intensity trajectories, and interventions that may shift trajectories towards lower intensity at EOL.

Matrix decomposition for modeling lesion development processes in multiple sclerosis.

Our main goal is to study and quantify the evolution of multiple sclerosis lesions observed longitudinally over many years in multi-sequence structural magnetic resonance imaging (sMRI). To achieve that, we propose a class of functional models for capturing the temporal dynamics and spatial distribution of the voxel-specific intensity trajectories in all sMRI sequences. To accommodate the hierarchical data structure (observations nested within voxels, which are nested within lesions, which, in turn, are nested within study participants), we use structured functional principal component analysis. We propose and evaluate the finite sample properties of hypothesis tests of therapeutic intervention effects on lesion evolution while accounting for the multilevel structure of the data. Using this novel testing strategy, we found statistically significant differences in lesion evolution between treatment groups.

Five-year Pain Intensity and Treatment Trajectories of Post-9/11 Veterans With Mild Traumatic Brain Injury

Pain is a pervasive problem that affects nearly half of the U.S. Veterans deployed in support of the Global War on Terror (Post-9/11 Veterans) and over half of the Post-9/11 Veterans with diagnosed traumatic brain injury (TBI). The goal of the current study was to identify pain phenotypes based on distinct longitudinal patterns of pain scores in light of pain treatment among Post-9/11 Veterans over 5 years of care using latent growth mixture analysis stratified by TBI status. Five pain phenotypes emerged: 1) simple low impact stable pain, 2) complex low impact stable pain, 3) complex low impact worsening pain, 4) complex moderate impact worsening pain, and 5) complex high impact stable pain. Baseline pain scores and slopes were significantly higher in Veterans with mild TBI for some phenotypes. The mild TBI cohort was younger, had more men, more whites, less blacks, less education, more unmarried, more Marines and Army, more active duty in comparison to the no TBI cohort. Distinct trajectories in pain treatment were apparent among the pain intensity subgroups. PerspectiveThe complexity of pain in patients with mTBI is categorically different than those with no TBI. Pain in patients with mTBI is heterogeneous with distinct phenotypes which may explain poor outcomes in this group. Identification of the individual differences may have a significant impact on the success of interventions.

A Center Location Algorithm for Tropical Cyclone in Satellite Infrared Images

The precise location of the tropical cyclone (TC) center is critical for intensity estimation and trajectory prediction. Due to the variability of TC morphology and structure, there are still some challenges in locating its center automatically. The ability of the deep convolutional network to capture multilevel structural features of the images is exploited. Furthermore, a two-step scheme for locating the TC center is proposed, which contains the object detection for TCs with deep learning and the comprehensive decision for TC centers. In the object detection, considering the statistical scale distribution of TCs, the global and local features extracted by the network are combined to form the fusion feature maps through the upsampling and concatenation. The changes in the TC scale are accommodated by two different scale outputs. A high detection rate and a low false alarm rate are obtained with the object detection, which provides an initial position for the TC center. Within the scope of the TCs, the final position of the center is obtained through segmentation, edge detection, circle fitting, and comprehensive decision. The experimental results show that the average latitude and longitude error of the proposed method is about 0.237$^\circ$. For the TC in the initial phase or dissipation stage, the location results are usually superior to the results of the comparison algorithms.

Applying infectious disease forecasting to public health: a path forward using influenza forecasting examples

BackgroundInfectious disease forecasting aims to predict characteristics of both seasonal epidemics and future pandemics. Accurate and timely infectious disease forecasts could aid public health responses by informing key preparation and mitigation efforts.Main bodyFor forecasts to be fully integrated into public health decision-making, federal, state, and local officials must understand how forecasts were made, how to interpret forecasts, and how well the forecasts have performed in the past. Since the 2013–14 influenza season, the Influenza Division at the Centers for Disease Control and Prevention (CDC) has hosted collaborative challenges to forecast the timing, intensity, and short-term trajectory of influenza-like illness in the United States. Additional efforts to advance forecasting science have included influenza initiatives focused on state-level and hospitalization forecasts, as well as other infectious diseases. Using CDC influenza forecasting challenges as an example, this paper provides an overview of infectious disease forecasting; applications of forecasting to public health; and current work to develop best practices for forecast methodology, applications, and communication.ConclusionsThese efforts, along with other infectious disease forecasting initiatives, can foster the continued advancement of forecasting science.

Pediatric Chronic Postsurgical Pain And Functional Disability: A Prospective Study Of Risk Factors Up To One Year After Major Surgery.

BackgroundChronic postsurgical pain (CPSP) is a surgical complication associated with increased functional disability, psychological distress, and economic costs. The aims of this paper were to prospectively: (1) examine the incidence of CPSP 6 and 12 months after pediatric major surgery; (2) identify pain intensity and pain unpleasantness trajectories before, and up to 12 months after, surgery; (3) identify pre-operative factors that predict pain trajectory group membership; and (4) identify predictors of 12-month functional disability.MethodsThis study followed 265 children aged 8–17 years at four time points (pre-surgical [T0], in-hospital [T1], 6 [T2] and 12 [T3] months after surgery). Children and parents completed pain and psychological questionnaires. In-hospital physical activity was monitored using actigraphy.Results and discussionThe incidence of moderate-to-severe CPSP at 6 and 12 months was 35% (95% CI 29.1% to 41.9%) and 38% (95% CI 32.4% to 45.1%), respectively. Three percent (95% CI 1.17% to 6.23%) and 4% (95% CI 1.45% to 6.55%) of children reported using opioids to manage pain at 6 and 12 months, respectively. Growth mixture modeling revealed a two-class trajectory model with a quadratic slope best fit the data for both pain intensity (Bayesian information criterion [BIC] = 3977.03) and pain unpleasantness (BIC = 3644.45) over the 12 months. Preoperative functional disability and cumulative in-hospital opioid consumption predicted pain intensity trajectories. Preoperative functional disability predicted pain unpleasantness trajectories. Preoperative functional disability (OR: 1.05, 95% CI: 1.01 to 1.09) and pain unpleasantness trajectories (OR: 2.59, 95% CI: 1.05 to 6.37) predicted 12-month moderate-to-severe functional disability.ConclusionPre-surgical functional disability is the only factor that predicts both 12-month functional disability and the course of pain intensity and pain unpleasantness ratings over the 12-month period.

Atividade turística em Natal e Tibau do Sul

Este artigo tem o objetivo de analisar as trajetórias de expansão do setor turístico no Rio Grande do Norte, estado situado na Região Nordeste do Brasil, considerando seus dois destinos mais importantes: Natal, capital estadual e Tibau do Sul, onde está localizada a praia de Pipa. O estudo comparativo da dinâmica dos empregos turísticos nesses dois municípios no período 2001- 2016 oferece indicações a respeito do peso do turismo na determinação do emprego ao longo do tempo nos mesmos. A hipótese que sustenta este trabalho é que enquanto a atividade turística em Natal experimentou perda de importância relativa, a inserção alcançada por Pipa nos mercados internacional e nacional tornou-a um produto turístico singular, determinando uma trajetória de crescimento mais intensivo dos negócios ligados ao setor e promovendo a concentração do emprego nesta localidade. Os resultados obtidos a partir do Quociente locacional (), do índice Hirschman- Herfindahl () e do índice de Participação Relativa () permitem aumentar o grau de confiança na hipótese formulada.
 Palavras-chave: Turismo. Emprego. Medidas de Especialização.

Time Off Work After Childbirth and Breastfeeding Supportive Workplaces: Associations with Near-Exclusive Breastfeeding Trajectory Membership.

We aimed to determine whether the association between time off work and a near-exclusive breastfeeding trajectory is moderated by perceived employer support for breastfeeding. We conducted a secondary analysis of working mothers (n=1,468) from the Infant Feeding Practices Study II, a longitudinal observational (2005-2007) study of U.S. infant feeding behaviors. Previous studies have found four latent infant feeding subgroups in the Infant Feeding Practices Study II sample, each following a distinct breastfeeding intensity trajectory. Multivariate least-squares regression was conducted to estimate whether time off work after delivery predicted increased membership in the subgroup characterized by near-exclusive breastfeeding, and whether this association was moderated by perceived employer support for workplace breastfeeding. Both time off work and perception of more breastfeeding support were independently, positively related to probability of membership in the near-exclusive breastfeeding trajectory (β=0.16, p=.019, and β=0.14, p=.004, respectively). The interaction of these two factors suggests an attenuation effect. The addition of paid leave to the model did not change the estimates. The positive relationship between time off and trajectory membership was significant only for mothers who perceived their workplaces to be unsupportive of breastfeeding.

Insights on heterogeneity in blinking mechanisms and non-ergodicity using sub-ensemble statistical analysis of single quantum-dots.

Photo-luminescence (P-L) intermittency (or blinking) in semiconductor nanocrystals (NCs), a phenomenon ubiquitous to single-emitters, is generally considered to be temporally random intensity fluctuations between "bright" ("On") and "dark" ("Off") states. However, individual quantum-dots (QDs) rarely exhibit such telegraphic signals, and yet, a vast majority of single-NC blinking data are analyzed using a single fixed threshold which generates binary trajectories. Furthermore, while blinking dynamics can vary dramatically over NCs in the ensemble, the extent of diversity in the exponents (mOn/Off) of single-particle On-/Off-time distributions (P(tOn/Off)), often used to validate mechanistic models of blinking, remains unclear due to a lack of statistically relevant data sets. Here, we subclassify an ensemble of QDs based on the emissivity of each emitter and subsequently compare the (sub)ensembles' behaviors. To achieve this, we analyzed a large number (>1000) of blinking trajectories for a model system, Mn+2 doped ZnCdS QDs, which exhibits diverse blinking dynamics. An intensity histogram dependent thresholding method allowed us to construct distributions of relevant blinking parameters (such as mOn/Off). Interestingly, we find that single QD P(tOn/Off)s follow either truncated power law or power law, and their relative proportion varies over subpopulations. Our results reveal a remarkable variation in mOn/Off amongst as well as within subensembles, which implies multiple blinking mechanisms being operational amongst various QDs. We further show that the mOn/Off obtained via cumulative single-particle P(tOn/Off) is distinct from the weighted mean value of all single-particle mOn/Off, evidence for the lack of ergodicity. Thus, investigation and analyses of a large number of QDs, albeit for a limited time span of a few decades, are crucial to characterize the spatial heterogeneity in possible blinking mechanisms.

Conformational Heterogeneity in Large Macrocyclic Thiophenes.

For conjugated macrocycles, conformational disorder plays a key role in determining whether the unique form of excitons that are fully delocalized over the cyclic framework (cyclic excitons) is formed by photoexcitation. We have investigated the ring size dependence of conformations and photophysical properties of macrocyclic thiophenes of varying ring sizes (C-5NTNV) by using single-molecule fluorescence spectroscopy. We measured modulation depth, M, values and fluorescence intensities. As the ring size increases, the correlation plots of the two parameters show bimodal distributions, revealing that larger macrocycles exhibit extremely congested linear structures. The size dependence of structural changes in macrocyclic thiophenes have been clearly confirmed by molecular dynamics simulation. The number of torsional defects from simulated structures, in conjunction with survival times from fluorescence intensity trajectories and photon coincidence measurements, demonstrated the existence of multiple acyclic chromophores in the larger macrocycles from the ground state due to complete deformation of circular structures.

Proposing a new indicator to combat procrastination over CO2 mitigation in China

A reduction in the CO2 emission intensity (ton per gross domestic product) from a base year to a target year with different rates of reduction in each individual year can yield different cumulative CO2 emissions over time, which could have different effects on the climate. In this paper, an indicator is proposed to measure the extent to which the cumulative CO2 emissions are generated by a specific reduction trajectory of CO2 emission intensity, especially for emerging economies with a relatively higher economic growth rate. The proposed indicator is important for less-developed countries and regions in which economic growth is heavily reliant on energy and in which significant potential exists for improvement of energy efficiency. The indicator is applied to evaluate the CO2 emission reduction performance in China’s 12th Five-Year Plan period, and the result is not encouraging, especially when the likely gap between the energy conservation goals and temperature goals is further examined. Mitigation goals should be set by considering not only the performance in the final year, but also the reduction in cumulative emissions over the evaluation period.

P030: Acute pain resolution after an emergency department visit: a 14-day trajectory analysis

Introduction: The objective of the study was to evaluate the acute pain intensity evolution in ED discharged patients using Group-based trajectory modeling (GBTM). This method identified patient groups with similar profiles of change over time without assuming the existence of a particular pattern or number of groups. Methods: This was a prospective cohort study of ED patients aged ≥18 years with an acute pain condition (≤ 2 weeks) and discharged with an opioid prescription. Patients completed a 14-day diary assessing daily pain intensity level (0-10 numeric rating scale) and pain medication use. Results: Among the 372 included patients, six distinct post-ED pain intensity trajectories were identified: two started with severe levels of pain, one remained with severe pain intensity (12.6% of the sample) and the other ended with moderate pain intensity level (26.3%). Two other trajectories had severe initial pain, one decreased to mild pain (21.7%) and the other to no-pain (13.8%). Another trajectory had moderate initial pain which decreased to a mild level (15.9%) and the last one started with mild pain intensity and had no pain at the end of the 14-day (9.7%). The pain trajectory patterns were significantly associated with age, type of painful conditions, pain intensity at ED discharge, and with opioid consumption. Conclusion: Acute pain resolution following an ED visit seems to progress through six different trajectory patterns that are more informative than simple linear models and could be useful to adapt acute pain management in future research.

P029: Are acute pain trajectories after an emergency department visit associated with chronic pain at 3 months?

Introduction: Studies suggest that acute pain evolution after an emergency department (ED) visit has been associated with the development of chronic pain. Using group-based trajectory modeling (GBTM), we aimed to evaluate if ED discharged patients with similar pain intensity profiles of change over 14 days are associated with chronic pain at 3 months. Methods: This is a prospective cohort study of patients aged 18 years or older who visited the ED for an acute pain condition (≤2 weeks) and were discharged with an opioid prescription. Patients completed a 14-day diary in which they listed their daily pain intensity level (0-10 numeric rating scale). Three months post-ED visit, participants were interviewed by phone to report their pain intensity related to the initial pain. Results: A total of 305 patients were retained at 3 months (mean age ± SD: 55 ± 15 years, 49% women). Using GBTM, six distinct pain intensity trajectories were identified during the first 14 days of the acute pain period; two linear one with moderate or severe pain during the follow-up (representing almost 40% of the patients) and four cubic polynomial order trajectories, with mild or no-pain at the end of the 14 days (low final pain). Twelve percent (11.9; ±95%CI: 8.2-15.4) of the patients had chronic pain at 3 months. Controlling for age, sex and types of pain condition, patients with trajectories of moderate or severe pain and those with only severe pain were 5.1 (95%CI: 2.2-11.8) and 8.2 (95%CI: 3.4-20.0) times more likely to develop chronic pain at 3 months, respectively, compared to the low final pain group. Conclusion: Trajectories could be useful to early identification of patients at risk of chronic pain.

Acute Pain Resolution After an Emergency Department Visit: A 14-Day Trajectory Analysis

The objective of the study is to evaluate the acute pain intensity evolution in emergency department (ED) discharged patients, using group-based trajectory modeling. This method identifies patient groups with similar profiles of change over time without assuming the existence of a particular pattern or number of groups. This was a prospective cohort study of ED patients aged 18 years or older, with an acute pain condition (≤2 weeks), and discharged with an opioid prescription. Patients completed a 14-day diary assessing daily pain intensity level (numeric rating scale of 0 to 10) and pain medication use. Among the 372 included patients, 6 distinct post-ED pain intensity trajectories were identified. Two started with severe levels of pain; one remained with severe pain intensity (12.6% of the sample) and the other ended with a moderate pain intensity level (26.3%). Two other trajectories had severe initial pain; one decreased to mild pain (21.7%) and the other to no pain (13.8%). Another trajectory had moderate initial pain that decreased to a mild level (15.9%) and the last one started with mild pain intensity and had no pain at the end of the 14-day period (9.7%). The pain trajectory patterns were significantly associated with age, type of painful conditions, pain intensity at ED discharge, and opioid consumption. Acute pain resolution after an ED visit seems to progress through 6 different trajectory patterns that are more informative than simple linear models and could be useful to adapt acute pain management in future research.

Novel Approach to Characterize Heterogeneity in an Aerobic Exercise Intervention.

Exercise intervention studies for brain health can be difficult to interpret due to heterogeneity in exercise intensity, exercise duration, and in adherence to the exercise intervention. This study aimed to characterize heterogeneity in these components in a cohort of healthy middle-age and older adults who participated in a prescribed 6-month supervised aerobic exercise intervention as part of the Brain in Motion study. Group-based multitrajectory analysis (GBMTA) was used to characterize variation in the trajectory of exercise intensity and duration for male and female participants in the first 3 months of the exercise program. The GBMTA for males and females revealed two distinct trajectory subgroups, namely, "high-increasing" (HI) and "low-increasing" (LI). Logistic regression was used to assess the association between the identified latent subgroups and (i) demographic characteristics; (ii) physiological characteristics, including cardiovascular and cerebrovascular function; (iii) genetic characteristics; and (iv) adherence with American College of Sports Medicine guidelines on exercise for older adults. Of the 196 participants, 54.1% met the American College of Sports Medicine aerobic exercise targets for intensity and duration during the intervention. Aerobic fitness (maximal oxygen uptake; odds ratio, 1.27; P < 0.01) was significantly different between these trajectory subgroups in males, and cerebrovascular function (cerebrovascular resistance; odds ratio, 0.14; P < 0.01) was significantly different between these trajectory subgroups in females. This novel approach to tracking a prespecified exercise program highlights that there are individual and group-specific variations within a prescribed exercise intervention. Characterizing exercise adherence in this way holds promise in developing optimized exercise prescriptions tailored to individual baseline characteristics, and additionally highlighting those participants at greatest risk of not meeting minimum dosage requirements for physiological and/or cognitive health.

In-hospital opioid consumption, but not pain intensity scores, predicts 6-month levels of pain catastrophizing following hepatic resection: A trajectory analysis.

The study aims were to model acute pain intensity and opioid consumption trajectories up to 72hr after open hepatic resection, identify predictors of trajectory membership and examine the association between trajectory memberships and 6-month pain and psychological outcomes. This is a long-term analysis of a published randomized controlled trial on the impact of medial open transversus abdominis plane catheters on post-operative outcomes. A total of 152 patients (89 males; mean age 63.0 [range: 54-72]) completed questionnaires on pain and related characteristics pre-operatively and 6months post-operatively. Total opioid use was recorded several times over a 72-hr period while self-reported pain intensity scores were collected multiple times until hospital discharge. Analyses were carried out using growth mixture modelling, logistic regression and general linear models. Both pain intensity and opioid consumption showed that a four-trajectory model best fits the data. Patients in the lowest opioid consumption trajectory were more likely to be classified in the constant mild pain intensity trajectory. Age and baseline levels of anxiety significantly predicted opioid trajectory membership while baseline depressive symptoms significantly predicted pain intensity trajectory membership. Patients in the two highest opioid consumption trajectories reported significantly higher levels of pain catastrophizing at 6months compared to patients in the other 3 trajectories (all p<0.05). High consumption of opioids after surgery is associated with higher levels of pain catastrophizing 6months later. Identification of patients within these trajectories may lead to the development of early interventions targeted to high risk individuals. Differences in initial levels of opioid consumption and rates of change in opioid consumption shortly after surgery can help predict long-term psychological responses to pain. Identifying key characteristics associated with initial opioid consumption can lead to the development of cost-effective early interventions targeted to high risk individuals.

Changes in Smoking During Retirement Transition: A Longitudinal Cohort Study.

Aims: We examined the effect of retirement transition on changes in smoking, identified trajectories of smoking around the retirement transition, and investigated factors predicting the membership in the trajectories. Methods: This longitudinal cohort study included 1,432 current or former smokers who entered into statutory retirement in 2000-2011 and who filled out two to four questionnaires sent at four-year intervals. Effect of retirement on smoking was analysed as a non-randomized pseudo-trial in which we compared the likelihood of quitting and relapsing smoking between two subsequent survey waves among those who retired and did not retire. We used latent class analysis to identify trajectories of smoking status and smoking intensity (low: <10 cigarettes/day or high: ⩾10 cigarettes/day), and multinomial logistic regression models to assess pre-retirement factors associated with smoking trajectories. Results: Retirement transition was associated with 1.7-fold odds of quitting smoking (95% confidence intervals 1.3-2.2) compared with no retirement transition. We identified three smoking status trajectories: 'sustained non-smoking' (61% of the participants), 'sustained smoking' (23%) and 'decreasing smoking' (16%). For 489 baseline smokers, we identified three smoking intensity trajectories: 'sustained high intensity smoking' (32% of the participants), 'sustained low intensity smoking' (32%) and 'decreasing high intensity smoking' (35%). Living outside an inner urban area predicted membership in the 'decreasing smoking' versus 'sustained smoking' trajectory. Conclusions: Smokers are more likely to quit smoking during transition to retirement than before or after it. Characteristics of the smoking environment may affect smoking behaviour around retirement.

Trajectory of thirst intensity and distress from admission to 4-weeks follow up at home in patients with heart failure.

BackgroundPatients with heart failure (HF) can suffer from increased thirst intensity and distress. Trajectories of thirst intensity and distress from hospital to home are unclear. The aim of this study was to describe thirst intensity and distress trajectories in patients from the time of hospital admission to 4 weeks after discharge, and describe trajectories of thirst intensity and distress by patients’ characteristics (gender, age, body mass index [BMI], plasma urea, anxiety, and depression).Patients and methodsIn this observational study, data were collected from patients with HF (n=30) at hospital admission, discharge, and at 2 and 4 weeks after discharge. Thirst intensity (visual analog scale, 100 mm) and distress (Thirst Distress Scale-HF, score 9–45) were used. Trajectories were examined using growth modeling.ResultsTrajectory of the thirst intensity was significantly different, for patients with low and high thirst intensity levels (median cut-off 39 mm), from admission to 4 weeks follow up (thirst increased and decreased, respectively). Patients with high level of thirst distress (median score >22) at admission, having fluid restriction and women continued to have higher thirst distress over time. Patients feeling depressed had higher thirst intensity over time. There were no differences in the trajectories of thirst intensity and distress by age, BMI, plasma urea, and anxiety.ConclusionIntensity and distress of thirst, having fluid restriction, and feeling depressed at the admission were critical in predicting the trajectory of thirst intensity and distress after discharge to home in patients with HF. Effective intervention relieving thirst should be provided before their discharge to home.

Digital footprints: Using WiFi probe and locational data to analyze human mobility trajectories in cities

City governments all over the world face challenges understanding mobility patterns within dense urban environments at high spatial and temporal resolution. While such measures are important to provide insights into the functional patterns of a city, novel quantitative methods, derived from ubiquitous mobile connectivity, are needed to provide policy-makers with better insights to improve urban management and planning decisions. In this paper, we develop a model that uses large-scale WiFi probe request data to model urban mobility trajectories in dense urban environments. We collect probe request data from a public Wifi network with 54 access points in the Lower Manhattan section of New York City over one week, accounting for more than 30 million observations and over 800,000 unique devices. First, we aggregate unique entries per access point and per hour, demonstrating the potential to use WiFi data to approximate local population counts by type of user. We then use a spatial network analysis to identify edge frequencies and directions of journeys between the network nodes, and apply the results to the road and pedestrian sidewalk network to identify usage intensity levels and trajectories for individual street segments. We demonstrate the significant potential in the use of WiFi probe request data for understanding mobility patterns in cities, while highlighting non-trivial issues in data privacy raised by the growing availability of public WiFi networks.

Ionization waves of arbitrary velocity driven by a flying focus

A chirped laser pulse focused by a chromatic lens exhibits a dynamic, or "flying," focus in which the trajectory of the peak intensity decouples from the group velocity. In a medium, the flying focus can trigger an ionization front that follows this trajectory. By adjusting the chirp, the ionization front can be made to travel at an arbitrary velocity along the optical axis. We present analytical calculations and simulations describing the propagation of the flying focus pulse, the self-similar form of its intensity profile, and ionization wave formation. The ability to control the speed of the ionization wave and, in conjunction, mitigate plasma refraction has the potential to advance several laser-based applications, including Raman amplification, photon acceleration, high harmonic generation, and THz generation.