Virginia Polytechnic Institute and State University
  • Blacksburg, Virginia, United States
Recent publications
Two major footbridge failures were reported during the nineteenth century when soldiers marched over them in unison. They resulted in large number of casualties. Even though modern footbridges are not generally in danger of failure due to such activities, they can be susceptible to vibrations when pedestrians move across them. These can become excessively large if people walk or march in unison at the footbridge resonance frequency or its subharmonics. The vibration serviceability issue of the Millennium Bridge over the Thames River in London is a well-known example of such problems. Therefore, it is essential for the structural designer to be able to predict the vibration response of the footbridge due to pedestrian movements with an acceptable accuracy. This paper details the vibration testing and computer modeling of a footbridge. The computer model has been updated to accurately represent the structure. The footbridge vibrations due to the movements of various groups of people at the subharmonics of its resonance frequency were measured. The computer model was then subjected to human footfall forces and the predicted responses were compared with those from the measurements. It is known that the human-structure interactions (HSI) can affect the predicted response of footbridges. However, the incorporation of HSI into a computer model is generally a complex process. By equating the computed and measured Vibration Dose Value (VDV), equivalent damping ratios of the structure due to the HSI effects were found which showed an almost linear increase with the number of the pedestrians.KeywordsFootbridge dynamic responseHuman-structure interaction (HSI)Structural modelingGround reaction force (GRF)Vibration dose value (VDV)
Excessive vibrations of architectural structures have become a prevalent design issue in recent years. The high strength of construction materials, optimized design of structures, and the desire of architects for large open space building layouts have resulted in a number of serviceability issues in existing building structures. In an attempt to search for an economical method of resolving this issue, a new multiple-tuned mass damper (MTMD) has been designed and tested. The device consists of four steel plates cantilevered from a central hub. Each plate (wing) has a central slot that can be used for the movement of steel weights to modify the natural frequencies of the MTMD during the tuning phase. In addition, air dampers connected to each wing provide the required damping for the optimal tuning of the MTMD. This paper details the design of this novel MTMD and provides the analytical equations developed for the tuning of the device. It also provides information on the field tuning of the device to a laboratory floor susceptible to large vibrations due to human movements. In addition, results of the walking and bouncing tests conducted at the Virginia Tech Vibration Testing Laboratory to evaluate the effectiveness of the device are discussed. It is concluded that the proposed device can provide an economical and effective method of floor vibration mitigation.KeywordsMultiple tuned mass damperFloor vibrationVibration serviceabilityMTMD tuningWalk and bounce excitations
The objective of this study was to quantify performance in an obstacle clearance task among individuals with excess body weight or body mass index (BMI). Task performance was operationalized as the maximum obstacle height cleared, four duration measures of successful task completion and compensatory movements used in the process of task completion. Eighteen participants with a BMI exceeding 30 kg/m² completed a laboratory experiment that required stepping over seven lightweight obstacles. Obstacle heights were sequentially increased from 36 cm in 5 cm increments until participants were unsuccessful or unable to clear the obstacle up to 66 cm. Successful task completions decreased from 100% at an obstacle height of 36 cm to 66.1% at 66 cm. Higher obstacle heights were associated with significantly fewer task completions, longer leading and trailing leg stance and overall task duration, and more frequent use of compensatory movements for successful obstacle clearance. Cox PH regression was used to test the association between probability of obstacle clearance and normalized obstacle height adjusting for BMI, standing balance, and type of compensatory movement used, namely, hover and pivot motions involving the leg, and hands for bracing. The probability of successful task completion significantly decreased with increases in BMI (hazard ratio, HR = 1.14, 95% CI: 1.05–1.25), and increased with use of a leg pivot motion (HR = 0.30, 95% CI: 0.09–0.96) during task completion, after adjusting for standing balance and other types of compensatory movements. Overall, the results demonstrated that obstacle clearance performance is affected by an individual's BMI and the use of compensatory behaviors for regaining stability. The ability to recruit internal and external stabilization techniques could potentially serve as a clinical indicator of reduced fall risk and be the focus of fall prevention interventions. Implications for evaluating stability, fall risk, and identifying modifiable factors for fall prevention in the obese population are discussed.
Postmortem changes that occur during the process of converting muscle to meat play a critical role in the development of quality traits and the overall acceptance of the fresh product. After an animal is harvested, muscle glycogen along with high-energy phosphate compounds is anaerobically metabolized in an effort to maintain adenosine triphosphate (ATP) homeostasis. As a consequence of postmortem glycolysis, lactate and hydrogen ions accumulate in the muscle and cause a drop in pH. Ultimately, postmortem metabolism is arrested due to substrate depletion or the inactivation of the glycolytic enzyme phosphofructokinase-1, resulting in ATP depletion and the development of rigor mortis. The muscle subsequently undergoes proteolytic disruption of myofibrillar proteins, thereby improving meat tenderness and flavor. Factors such as genetics, nutrition, environmental conditions, and pre- and postmortem handling can drastically influence the conversion of muscle to meat and ultimately end-product quality.
A robust unbalanced Gires-Tournois interferometer (GTI) mirror for evaluating group delay dispersion (GDD) measurement by scanning white light interferometer is presented, and a novel processing algorithm based on scanning white light interferometer (WLI) is proposed to extract group delay and group delay dispersion characteristics with improved accuracy and low level of noise. The GDD measurement evaluation method is based on error analysis of manufacturing errors and spectral measurement. Spectral measurement is carried out to determine the resonance wavelength of GTI mirror. The sample was prepared by ion beam sputtering deposition. The relative errors of refractive index and layer thickness for the sample are estimated through reverse engineering based on multi-angle transmittance measurements. A novel processing algorithm the extrema searching method (ESM) is proposed that search the positions of multi-order extrema from reconstructed interferogram intensity to exact the GDD characteristics of the sample. GDD measurements performed by WLI with different processing methods are added to comparison including windowed Fourier transform, wavelet transform and time-domain scanning method. The results show that our method is reliable and effective for GDD measurement with a good accuracy and low level of noise.
Rationale Current hepatic locoregional therapies are limited in terms of effectiveness and toxicities. Given promising pre-clinical results, a first in-human trial was designed to assess the technical effectiveness and safety profile of histotripsy, a noninvasive, non-thermal, non-ionizing focused ultrasound therapy that creates precise, predictable tissue destruction, in patients with primary and secondary liver tumors. Methods A multicenter phase I trial (Theresa Study) was performed in a single country with 8 weeks of planned follow-up. Eight of fourteen recruited patients were deemed eligible and enrolled in the study. Hepatic histotripsy, was performed with a prototype system (HistoSonics, Inc., Ann Arbor, MI). Eleven tumors were targeted in the 8 patients who all had unresectable end-stage multifocal liver tumors: colorectal liver metastases (CRLM) in 5 patients (7 tumors), breast cancer metastases in 1 (1 tumor), cholangiocarcinoma metastases in 1 (2 tumors), and hepatocellular carcinoma (HCC) in 1 (1 tumor). The primary endpoint was acute technical success, defined as creating a zone of tissue destruction per planned volume assessed by MRI 1-day post-procedure. Safety (device-related adverse events) through 2 months was a secondary endpoint. Results The 8 patients had a median age of 60.4 years with an average targeted tumor diameter of 1.4 cm. The primary endpoint was achieved in all procedures. The secondary safety profile endpoint identified no device-related adverse events. Two patients experienced a continuous decline in tumor markers during the eight weeks following the procedure. Conclusions This first-in-human trial demonstrates that hepatic histotripsy effectively destroys liver tissue in a predictable manner, correlating very well with the planned histotripsy volume, and has a high safety profile without any device-related adverse events. Based on these results, the need for more definitive clinical trials is warranted. Trial Registration: Study to Evaluate VORTX Rx (Theresa). NCT03741088. https://clinicaltrials.gov/ct2/show/NCT03741088 • KEY POINTS • Histotripsy, a new noninvasive, non-thermal, non-ionizing focused ultrasound therapy, safely created a zone of tissue destruction in the liver that correlated very well with the pre-defined planned tissue destruction volume. • In this first human trial histotripsy was well tolerated with no histotripsy device-related adverse events and its primary endpoint of acute technical success was achieved in all 8 enrolled patients with primary or secondary liver tumors. • This new locoregional therapy for patients with liver tumors is safe and effective, warranting further trials.
Background Sports and recreational activities are the most commonly reported cause of injury-related emergency department (ED) visits among children and young adults in developed countries, yet studies about the effect of neighborhood environment on sports and recreational injuries (SRI) are very limited. The aim of this study was to systematically review studies that apply multilevel modeling approach in examining the relationships between SRI and neighborhood-level risk factors. Data sources A systematic search of peer reviewed English language articles was conducted in four electronic databases including PubMed (1992–2020), CINAHL (2000–2020), Sports Medicine and Education Index (1996–2020), and Web of Science (1991–2020). Study selection Selected studies were observational or experimental studies of people of all ages across the world that assessed neighborhood risk factors for SRI (or all injuries including SRI) using multilevel regression analysis. Data synthesis Nine studies—five cross-sectional, two prospective cohort, and two incidence studies—were selected out of a potential 1510. Six studies used secondary data and three used primary data. Only three studies examined SRI as the main or one of the main outcomes. These studies showed that neighborhood-level factors, such as higher socioeconomic context, lower street connectivity, and living or attending schools in urban communities, were associated with increased risk of SRI. Most studies did not provide a justification for the use of multilevel regression and the multilevel analytical procedure employed and quantities reported varied. The Quality Assessment Tool for Observational Cohort and Cross-Sectional Studies (National Institutes of Health) was used to assess the quality or risk of bias of each study. Four quality assessment criteria out of 15 were met by all nine studies. The quality assessment ratings of the reviewed studies were not correlated with the quality of information reported for the multilevel models. Conclusion Findings from this review provide evidence that neighborhood-level factors, in addition to individual-level factors, should be taken into consideration when developing public health policies for injury prevention. Considering the limited numbers of studies that were identified by this systematic review, more multilevel studies are needed to strengthen this evidence in order to better inform SRI prevention policy decisions.
Background Neurogenesis in the hippocampus endures across the lifespan but is particularly prolific during the first postnatal week in the developing rodent brain. The majority of new born neurons are in the dentate gyrus (DG). The number of new neurons born during the first postnatal week in the DG of male rat pups is about double the number in females. In other systems, the rate of cell proliferation is controlled by epigenetic modifications in stem cells. We, therefore, explored the potential impact of DNA methylation and histone acetylation on cell genesis in the developing DG of male and female rats. Methods Cell genesis was assessed by quantification of BrdU + cells in the DG of neonatal rats following injections on multiple days. Methylation and acetylation were manipulated pharmacologically by injection of well vetted drugs. DNA methylation, histone acetylation and associated enzyme activity were measured using commercially available colorimetric assays. mRNA was quantified by PCR. Multiple group comparisons were made by one- or two-way ANOVA followed by post-hoc tests controlling for multiple comparisons. Two groups were compared by t test. Results We found higher levels of DNA methylation in male DG and treatment with the DNA methylating enzyme inhibitor zebularine reduced the methylation and correspondingly reduced cell genesis. The same treatment had no impact on either measure in females. By contrast, treatment with a histone deacetylase inhibitor, trichostatin-A, increased histone acetylation in the DG of both sexes but increased cell genesis only in females. Females had higher baseline histone deacetylase activity and greater inhibition in response to trichostatin-A treatment. The mRNA levels of the proproliferative gene brain-derived neurotrophic factor were greater in males and reduced by inhibiting both DNA methylation and histone deacetylation only in males. Conclusions These data reveal a sexually dimorphic epigenetically based regulation of neurogenesis in the DG but the mechanisms establishing the distinct regulation involving DNA methylation in males and histone acetylation in females is unknown.
This study investigated how film franchise fans with varying levels of fanship perceive subtle versus explicit signals featured on fan-themed apparel products. A between-subjects experimental design was conducted with two fan-themed t-shirt designs (explicit vs. subtle) × fanship (low vs. high). In this study, the joint effect between subtle vs. explicit designs and fanship was examined to address perceived differentiation, social connection, and purchase intention. For perceived differentiation and social connection, fans with high fanship perceived the subtle design to be more effective than explicit designs. While fans with low fanship perceived the subtle design to be more effective for differentiation, they perceived that the explicit design facilitated social connection more than the subtle design. When fans perceived that signals featured on fan-themed apparel products differentiated themselves from others and facilitated social connection, their purchase intentions increased. The study yielded several theoretical and practical implications. First, the study contributed to the literature on signaling theory, extending the definition of subtle signals to include a more diverse range of design details, such as the content of graphics rather than the visibility and size of brand logos. The study also extended the use of signaling theory and optimal distinctiveness theory to new research areas of fan-themed products. Second, practical implications for producers, marketers, and retailers of fan-themed apparel included the consideration of developing fan-themed apparel with subtle signals, co-creating products with fans, and targeting female fans through more inclusive merchandising practices.
Customer-to-customer (C2C) interactions can be realised through other customers’ responses (OCRs) in the online review system. However, the externality of such interactions has not been clearly understood. We address this deficiency by exploring the effects of OCRs on subsequent review volume. Drawing on social learning theory and reinforcement theory, we hypothesise that OCRs have positive effects on subsequent review volume through the visibility mechanism. We verify this hypothesis by matching restaurants across two online platforms using a difference-in-differences strategy. The results show that restaurants with OCRs show an average increase of 5.286 reviews per month, but the effect fades if subsequent customers have not observed OCRs in the last five review pages. We further validate the visibility mechanism and conduct robustness checks by examining review heterogeneity and performing within-platform analysis. Our findings highlight the importance of C2C interactions and provide implications for the design and management of online review systems.
Background Hemoglobinopathies represent a set of inherited red blood cell (RBCs) disorders, characterized by abnormal hemoglobin molecule. They include qualitative and quantitative hemoglobinopathies, with a structurally abnormal globin chain in the first and defective production in the later. This study assessed, for the first time, the significance of the mathematically calculated RBC indices to identify patients with hemoglobinopathies from normal subjects or iron deficiency anemia (IDA) and to differentiate various types of hemoglobinopathies from each other. Subjects and methods The study was a comparative hospital based and included 167 participants with hemoglobinopathies (group 1) and 49 participants with IDA (group 2) as an active comparator. Another 50 healthy volunteers (group 3) were also included. All participants were subjected to medical history, clinical examination, CBC, and HPLC. Next, 10 RBC indices were mathematically calculated from the CBC for each participant. Results Gender analysis shows that females represent 36.8% in thalassemia group, 42% in sickle cell disease (SCD) group, and 71.4% in IDA group. The receiver operating characteristic (ROC) curve shows that Ehsani index (EI) is the most reliable screening tool for thalassemics because of showing the highest Youden index and specificity of 41.88% and 88.89%, respectively, followed by Shine and Lal index (SL), with Youden index (YI) value, specificity, and sensitivity equal to 39.78%, 69.70%, and 70.09%, respectively. Similar results were found for IDA. For SCD, SL index is the most suitable screening tool. In conclusion, the mathematically calculated RBC indices are available, cheap, reliable, and sensitive tools for screening patients with hemoglobinopathies.
This letter presents a family of filter topologies for circulating current and conducted emissions mitigation, applicable with parallel and interleaved converters. The proposed alternative topologies are aimed at reducing the overall filter volume using magnetic integration or topological variations. In general, they are classified into three distinct forms, namely in-directly coupled, localized and direct phase to phase coupled topologies. The emphasis is on pure common mode (CM) harmonics but can be extended to differential mode (DM) components as well. A quantitative comparison among the variants is made on the basis of simulation/experimental findings and references aiding the designer to select the structure best suited for a particular application.
Modeling infiltration in water-repellent soils is difficult, as the underlying processes remain poorly quantified. However, recent work has adapted the Beerkan Soil Transfer Parameter (BEST) algorithm to include an exponential correction term for characterizing these types of soils. The original BEST-WR (WR = Water Repellent) method used a two-term approximate expansion of the Haverkamp quasi-exact implicit model. However, the BEST-WR method can have considerable inaccuracy, particularly as the time of infiltration and the soil water repellency increase. Here, we extended the BEST-WR model by adapting a three-term approximation of the Haverkamp quasi-exact implicit model to water-repellent soils. We then tested the new method using analytical data. For highly water-repellent soils, the proposed method had better performance when estimating soil sorp-tivity (S) and soil saturated conductivity (K s), with respective errors of less than 1.5 % and 8 %, compared to relative errors of more than 10 % and 30 % with the two-term BEST-WR method. We also tested both approaches with experimental data. The two methods provided similar estimates for hydraulic parameters, with linear correlations between methods of R 2 = 0.84 for S and R 2 = 0.88 for K s. Initial infiltration was not well modeled by either the two-term or three-term model for 33 tests, thus revealing limitations in the applied exponential model that we used to account for soil repellency. Nonetheless, the proposed three-term expression provided better fits than the two-term model for most of the infiltration runs, meaning that this new approach is more robust when modeling infiltration processes in water-repellent soils.
The interactions between ants and certain sap-feeding insects in the order Hemiptera are classic examples of food-for-protection mutualisms. In these associations, herbivorous hemipterans use a highly specialized, straw-like mouthpart to consume sap directly from plant phloem and xylem and, as a result, excrete a sugar-rich waste product called honeydew. Ant foragers in turn use specialized adaptations to collect and share honeydew with nestmates and, in exchange, protect hemipterans against predators. The two key innovations underlying this interaction—hemipteran sap feeding and ant harvesting of honeydew—have driven the evolutionary success and ecological dominance of ants. These interactions also carry unique costs and benefits for each partner and are highly context dependent. Understanding the factors mediating this mutualism is critical, as these interactions have broader ecological consequences for the natural and agricultural ecosystems in which they are embedded. Expected final online publication date for the Annual Review of Ecology, Evolution, and Systematics, Volume 53 is November 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.
The current study investigates whether prepregnancy maternal posttraumatic stress disorder (PTSD) symptoms, depressive symptoms, and stress predict children's cortisol diurnal slopes and cortisol awakening responses (CARs) adjusting for relevant variables. Mothers were enrolled after delivering a baby and followed through their subsequent pregnancy with 5 years of longitudinal data on their subsequent child. This prospective design allowed assessment of PTSD symptoms, depressive symptoms, and perceived stress prior to pregnancy. Children provided three saliva samples per day on three consecutive days at two timepoints in early childhood (M age = 3.7 years, SD = 0.38; M age = 5.04 years, SD = 0.43). Mothers’ PTSD symptoms prior to pregnancy were significantly associated with flatter child diurnal cortisol slopes at 4 and 5 years, but not with child CAR. Findings at the age of 4 years, but not 5 years, remained statistically significant after adjustment for maternal socioeconomic status, race/ethnicity, child age, and other covariates. In contrast, maternal prepregnancy depressive symptoms and perceived stress did not significantly predict cortisol slopes or CAR. Results suggest that maternal prepregnancy PTSD symptoms may contribute to variation in early childhood physiology. This study extends earlier work demonstrating risk of adverse outcomes among children whose mothers experienced trauma but associations cannot be disentangled from effects of prenatal mental health of mothers on children's early childhood.
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Stefanie Robel
  • Virginia Tech Carilion School of Medicine and Research Institute
Manisha Singal
  • Department of HT Management
Joseph S Merola
  • Department of Chemistry
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