University of Nevada, Reno
  • Reno, NV, United States
Recent publications
In recent years, researchers have shown interest in blocking low-frequency vibrations with the aid of metamaterials due to their inherent wave-filtering properties. However, proposing a practical metamaterial layout remains a challenge, taking into consideration the size, shape, and availability of metamaterial components. This study proposes a new configuration that can increase the range of the attenuation frequency. The configuration focuses on the capability of graded metamaterials in filtering a wide range of wave frequencies that can be generated by low-amplitude waves. To find the best configuration with the widest bandgap, square periodic sections using different materials including steel, rubber, concrete, tungsten, and carbon fiber-reinforced polymer were considered. Unit cells with two layers of materials were examined numerically to determine the attenuation zones and the effect of material properties and core size on the bandgap width and frequency range. Furthermore, the performance of the unit cells in a soil medium under the low-amplitude low-frequency surface and bulk waves is evaluated in the frequency domain using finite element analysis, in which the metamaterial is embedded periodically in a soil medium with different configurations, including a graded distribution. The results show that having an array of unit cells spaced periodically can decrease the transmission of the wave to the protected zone located after the array, and the application of grading can increase the attenuation zones to filter frequencies as low as 4.5 Hz and up to 29 Hz
Background As the legalization of cannabis moves forward in many countries, it is important to highlight the potential harm that excessive use can cause on young consumers. Crafting effective policy interventions to reduce the harm stemming from excessive use requires an understanding of the attitudes and motivations of young consumers. Methods This article uses Q methodology to study four aspects of cannabis use among young adults from Mexico City’s metropolitan area: motivations for use, perceived consequences of use, reasons that would increase willingness to reduce consumption, and attitudes towards government regulation. A total of 110 cannabis users between 18 and 21 years old were recruited using chain-referral sampling. Using a Q methodology, we captured the relative importance that participants assigned to a series of statements and identified archetypal profiles of young adults who use cannabis for each of the four aspects mentioned above. Results The sample for this research study included 76 men and 34 women. The average age of participants was 20 years old, and the average age when cannabis consumption started was 15 years old. For each of the four Q-sort factor analyses, we identified 4 distinct factors based on explained variance and interpretability. The Q factor analysis indicated that attenuation of a negative affect (i.e., anxiety, stress) and relaxation were primary motivations for cannabis use. Understood consequences of cannabis use ranged across aspect-archetype, reflecting legal (i.e., interacting with law enforcement), financial, familial (i.e., disappointing family members), and educational performance concerns. Participants indicated that finding alternative relaxation strategies, receiving credible evidence of the health harms of cannabis use, increased financial burden of purchasing, and increased inaccessibility of cannabis products would motivate reductions in use. Across archetypes, participants indicated a willingness to comply with cannabis policies which are simple and easy to understand, which do not lead to discrimination or law enforcement involvement, and which provide for legal places to purchase and use safe (i.e., free of adulterants) cannabis products. Conclusions We posit that these archetypes could be useful to inform cannabis policy design. As the study reveals, participants’ cannabis use was primarily motivated by perceived improvements to mental health. Furthermore, participant responses indicated that they viewed cannabis use as a health matter, not a criminal one. Policies which aim to promote alternative mental health wellness and relaxation mechanisms, which aim to improve communication of potential health harms of cannabis, and which allow for the safe and legal purchase and use of cannabis may be effective in reducing cannabis-associated harms. Though our findings shed light on important aspects of cannabis users’ attitudes and perspectives, the sample size does not allow for a generalization of the findings and the drawing of conclusions about the population under scrutiny. Further research should consider the application of the Q methodology used in this article to a larger and more representative sample of cannabis users.
Urban traffic congestion and crashes have been considered by city planners as critical challenges to the economic development of the city. Traffic signal coordination, which connects a series of signals along an arterial by various coordination methodologies, has been proved as one of the most cost-effective means of reducing traffic congestion. In this regard, Metropolitan Planning Organizations (MPO) or Transportation Management Centers (TMC) have included signal timing coordination in their strategic plans. Nevertheless, concerns on the safety effects of traffic signal coordination have been continuously raised by both transportation agencies and the public. This is mainly because signal coordination may increase the travel speed along an arterial, which increases the risk and severity of traffic collisions. To date, there is neither solid evidence from the field to support the concern, nor theoretical-level models to analyze this issue. This research aims to investigate the effects of traffic signal coordination on the safety performance of urban arterials through microsimulation modeling of two traffic operational conditions: free signal operation and coordinated signals, respectively. Three urban arterials in Reno, Nevada were selected as the simulation testbed and were coded in the PTV VISSIM software. The simulated trajectory data were analyzed by the Surrogate Safety Assessment Model (SSAM) to estimate the number of traffic conflicts. Sensitivity analyses were conducted for various traffic demand levels. Results show that under unsaturated conditions, traffic signal coordination could reduce the number of conflicts in comparison with the free signal operation condition. However, under oversaturated conditions, no significant difference was found between coordinated and free signal operations. Findings from this research indicate that traffic signal coordination has the potential to reduce the risk of crashes on urban arterials under unsaturated conditions.
This letter draws attention to recent work supporting the notion that the SARS-CoV-2 virus may use the nervus terminalis rather than the olfactory nerve as a shortcut route from the nasal cavity to infect the brain.
Background: The COVID-19 pandemic has been accompanied by increases in cannabis consumption, which might relate to dispensary marketing activities. As part of an ongoing project monitoring cannabis dispensary websites in Northern California and Reno, Nevada, we noticed many websites added announcements and "pop-up" communications in response to lockdowns. This brief report describes the cannabis dispensary website communications related to COVID-19 with the aim to provide insight into emerging marketing messages that may increase cannabis consumption in times of crisis. Methods: Content analysis of COVID-19 announcements present on cannabis dispensary websites in San Francisco/Alameda Counties (n = 32), and the Reno area (n = 15) in April-May 2020 shortly after lockdowns were implemented. Results: COVID-19 announcements were present on 25/32 (78%) of dispensary websites in San Francisco/Alameda and 9/15 (60%) of websites in the Reno area. Almost all COVID-19 announcements (88% San Francisco/Alameda, 89% Reno) announced operational changes such as delivery or curbside pickup services, 72% and 56% respectively announced patron/employee safety measures. Health related messages were present; about half of website announcements referred to government/health authorities, 44% of Reno area announcements used healthcare rhetoric, and some San Francisco/Alameda announcements included suggestions for using cannabis to mitigate infection risk or manage anxiety. Conclusions: Most cannabis dispensaries in the study region implemented COVID-19 pandemic operational changes to maintain product availability, and many positioned their identity with health - either by referring to health authorities, or using health rhetoric, and a minority gave health advice. Cannabis dispensary websites provide a timely snapshot of marketing practices that may contribute to increases in cannabis use during stressful events.
Many leaders in medical education have called for the inclusion of students with disabilities. Yet, a small number of review articles have been written summarizing the key literature addressing this topic. This review focuses on literature published between 2000 and 2021 that discusses medical education disability-specific barriers, student disability prevalence, and available institutional disability resources. Barriers include lack of procedure for students with disabilities to access services, delays in education to address disability needs, identified institutional disability resource professional (DRP), structural and physical barriers, outdated policies, and lack of understanding of accommodations needed in all educational settings, especially clinical. Medical school stakeholders must clearly understand the published literature on this topic to promote the full inclusion of students with disabilities.
Once installed, underground concrete pipes with rubber gaskets might be exposed to contaminated soil and groundwater. A pipe material monitoring capsule (PMMC) has been developed to evaluate volatile organic compounds (VOCs) breaking through three types of pipe gaskets; Neoprene, Buna-N, and Viton. The PMMCs were deployed in three contaminated sites: two with gasoline and one with chlorinated solvent (CS). A 3-D field-domain numerical model has been developed for each site to calibrate equivalent hydraulic parameters of each gasket material (ke, D) against benzene and PCE diffusion. The calibrated parameters were then used to compute the concentrations as well as rate of breakthrough of the two study contaminants. A protocol was developed for installing/retrieval of PMMCs to monitor PCE and benzene mass breaking through the gasket material with time. Employing PMMC, benzene concentrations breaking through the Neoprene and Buna-N after 4 months were approximately 70% and 60% respectively of the monitoring wells concentration. The corresponding value for PCE breakthrough after 4 months was 60% for both the Neoprene and Buna-N. Both gasket materials of Neoprene and Buna-N yielded similar performances, including higher rate of contaminant breakthrough compared to Viton. A nonlinear relationship of mass breaking through the gaskets of benzene and PCE with time was discerned from the modeling and field data.
In this mixed methods research, we analyzed the extent to which pre- and in-service teachers' attitudes towards linguistic diversity predicted their attitudes towards English Learner (EL) content-area instruction in the United States. We also analyzed participants' open-ended responses regarding their attitudes towards EL content-area instruction. 195 pre-service (N = 136) and in-service (N = 59) teachers enrolled in university coursework participated. Multiple regression models indicated attitudes towards linguistic diversity was a significant and large contributor to participants’ attitudes towards EL content-area instruction. Qualitative analysis revealed pre-and in-service teachers differed in attitudes towards working with English Learners (ELs) in the content-areas.
While many animals utilize socially transmitted information, there is still much to understand about how individuals form social networks and how these networks influence social information use. Here, we tested the hypothesis that food distribution and availability can influence social structure and social information transfer when discovering novel food sources. We experimentally manipulated distribution and access to food in wild food-caching mountain chickadees, Poecile gambeli, by randomly dividing existing individuals between two feeding locations, with birds only allowed to obtain food at one of the two locations. We carried out such manipulations at multiple sites associated with two montane elevations of different environmental harshness, where birds show differing use of social information. Following 2 weeks of manipulation, we measured social networks and then introduced novel feeders to test how the manipulation affected social information use. The manipulations effectively split the resident chickadees at both elevations into two distinct communities, and when subsequently discovering novel feeders, information transmission about novel food sources followed the new, rather than the premanipulation, network structure at both elevations, although low-elevation birds used social information more than high-elevation birds. Our data show that chickadees can quickly adjust their social associations in response to short-term changes in the distribution of available resources and that these changes influence who they learn from socially when searching for food. Overall, we observed that chickadees are highly flexible in their use of social information despite their rather stable social group structure and that this information use reflects the most current social environment that individuals experience.
Research-based professional development opportunities for early childhood home visitors are valuable to the Early Head Start-Home-Based Option (EHS-HBO) and to the home visiting field broadly to strengthen effective practice. We explored EHS-HBO home visitors' (N = 5) perspectives on effective practice through a professional development activity that included viewing videos of their own practice, analyzing the video and assessment data of their practice and parent-child interactions, and reflection. A convergent mixed methods multiple-case study was used. A variety of skills were noted within each case as indicators of effective practice, suggesting that a plethora of complex skills are needed to work with families. Across-case analytic strategies were used to compare subthemes, codes, and substantial statements across cases to generate themes. Two major themes emerged from our data analysis across cases: practicing self-reflective consciousness and building foundations for parent-child interactions. The findings have implications for professional development activities. Supplementary information: The online version contains supplementary material available at 10.1007/s10643-021-01249-3.
Cu-Al-Mn (CAM) superelastic alloys (SEAs) have been shown to improve the seismic performance of bridges and buildings by replacing the plastic hinge steel reinforcement. Despite research on mechanical performance at the material and structural scales, there is limited data on the degradation in the properties of CAM SEAs under harsh environmental conditions; particularly, under long-term corrosion that are relevant for civil engineering structures. This research aims to fill this knowledge gap by studying the long-term corrosion resistance of CAM SEAs in comparison with different types of steel reinforcing bars (rebar) used in construction. Long-term accelerated corrosion testing of CAM SEAs and four types of commonly used steel rebar, namely, mild steel (MS), high chromium steel (XS), epoxy coated steel (ES), and stainless steel (SS), was conducted up to 1,051 days. Three different diameters (U.S. #3, Φ = 9.53 mm; U.S. #5, Φ = 15.88 mm, and U.S. #10, Φ = 32.26 mm) of steel rebar were considered to determine the effect of bar size on the corrosion rate. Mechanical tests were conducted after specimens reached predetermined corrosion levels. The critical mechanical properties of CAM SEAs and four steel rebar were extracted and analyzed. In addition, potentiodynamic polarization tests were performed and the Tafel curves were employed to determine the corrosion rates of CAM SEAs, steel rebar and NiTi SEAs. NiTi alloy was used as a reference for being the more traditional composition used as SEAs. It was found that the corrosion resistance of CAM SEAs is higher than MS and XS, but lower than NiTi SEA, SS and ES. The superelasticity, particularly the strain recovery, of CAM SEAs showed almost no degradation after over three years of corrosion. The experimental data and control groups in this research provide detailed evaluation of the corrosion resistance of CAM SEAs and guides the application of CAM SEAs in harsh environmental conditions.
Long-lived species of trees, especially conifers, often display weak patterns of reproductive isolation, but clear patterns of local adaptation and phenotypic divergence. Discovering the evolutionary history of these patterns is paramount to a generalized understanding of speciation for long-lived plants. We focus on two closely related yet phenotypically divergent pine species, Pinus pungens and P. rigida, that co-exist along high elevation ridgelines of the southern Appalachian Mountains. In this study, we performed historical species distribution modeling (SDM) to form hypotheses related to population size change and gene flow to be tested in a demographic inference framework. We further sought to identify drivers of divergence by associating climate and geographic variables with genetic structure within and across species boundaries. Population structure within each species was absent based on genome-wide RADseq data. Signals of admixture were present range-wide, however, and species-level genetic differences associated with precipitation seasonality and elevation. When combined with information from contemporary and historical species distribution models, these patterns are consistent with a complex evolutionary history of speciation influenced by Quaternary climate. This was confirmed using inferences based on the multidimensional site frequency spectrum, where demographic modeling inferred recurring gene flow since divergence (2.74 million years ago) and population size reductions that occurred during the last glacial period (~ 35.2 thousand years ago). This suggests that phenotypic and genomic divergence, including the evolution of divergent phenological schedules leading to partial reproductive isolation, as previously documented for these two species, can happen rapidly, even between long-lived species of pines.
Determining the concentration of the dissolved lanthanide species in LiCl–KCl eutectic salt is important to the development of pyrochemical reprocessing of used nuclear fuel. In this process, lanthanide fission products are found dissolved in the electrorefiner electrolyte in their trivalent oxidation state. The presence of dissolved trivalent lanthanides increases the liquidus temperature of the electrolyte mixture and can lead to the formation of insoluble oxide or oxychloride phases and must therefore be continuously monitored and controlled during the operation. Absorbance spectroscopy is a promising method for continuous measurement of the concentration of lanthanides and other elements dissolved in the electrolyte. The absorption of light by elements is linearly proportional to the concentration of the element for relatively dilute solutions according to the Beer-Lambert law. Although measurement of the absorption of ultraviolet and visible range light by lanthanides in LiCl–KCl eutectic molten salt have been explored previously, near infrared (NIR) absorption spectroscopy has received far less attention. It may, however, provide a better analytical signal when insoluble phases are present due to less Raleigh scattering compared to shorter wavelength radiation. Additionally, it may allow for concentration determination for certain elements using NIR absorption features where UV and visible range features are overlapping with features from other species. In this study, we report the UV–Vis–NIR spectra of the trivalent lanthanide chlorides of neodymium, samarium, and dysprosium in LiCl–KCl eutectic. Molar absorption coefficients are reported for analytically useful absorption maxima, with a focus on the molar absorption coefficients for NIR absorption maxima which have not been reported previously. Additionally, we observe a NIR-range absorption band of Nd³⁺ which was previously predicted but never experimentally observed. We compare the calculated crystal field levels to the newly observed absorbance band and find them to be in good agreement with previous predictions.
Polymer modification of asphalt binders has progressively become more common over recent decades. Styrene-Butadiene-Styrene (SBS) is a well-recognized elastomer that has been commonly used in asphalt pavements. SBS polymer specifically exhibits a chemical morphology of hard polystyrene segment tethered by soft polybutadiene segment. Concerns related to binder pump clogging and reduced mixture workability have limited the SBS copolymer content in polymer-modified asphalt (PMA) to around 3 %. This motivated researchers to develop a new SBS polymer structure by modifying the midblock structure to have much higher vinyl content. High polymer-modified (HP) binder technology allowed the use of SBS at higher levels of 7–8 %. Although several studies have highlighted the positive impacts of HP on asphalt binders, they were mostly limited to the linear viscoelastic (LVE) domain. Therefore, there is still a need for a comprehensive evaluation of HP binders that considers failure properties, which constituted the main motivation of this research. In this study, Multiple Stress Creep Recovery (MSCR), Double Edge Notched Tension (DENT) and Asphalt Binder Cracking Device (ABCD) test results showed that HP binders exhibited superior performance compared to PMA in terms of higher strain recovery and lower non-recoverable creep compliance at high temperatures (52–70 °C), higher strain tolerance at intermediate temperature (25 °C), and lower (colder) cracking temperatures at sub-zero temperatures. Additionally, chemical analysis showed minimal HP degradation potential compared to PMA.
We present a theoretical study of quantum coherent dynamics of a three-level Λ-system driven by a thermal environment (such as blackbody radiation), which serves as an essential building block of photosynthetic light-harvesting models and quantum heat engines. By solving nonsecular Bloch–Redfield master equations, we obtain analytical results for the ground-state population and coherence dynamics and classify the dynamical regimes of the incoherently driven Λ-system as underdamped and overdamped depending on whether the ratio Δ/[ rf( p)] is greater or less than one, where Δ is the ground-state energy splitting, r is the incoherent pumping rate, and f( p) is a function of the transition dipole alignment parameter p. In the underdamped regime, we observe long-lived coherent dynamics that lasts for τ c ≃ 1/ r, even though the initial state of the Λ-system contains no coherences in the energy basis. In the overdamped regime for p = 1, we observe the emergence of coherent quasi-steady states with the lifetime τ c = 1.34( r/Δ ² ), which have a low von Neumann entropy compared to conventional thermal states. We propose an experimental scenario for observing noise-induced coherent dynamics in metastable He* atoms driven by x-polarized incoherent light. Our results suggest that thermal excitations can generate experimentally observable long-lived quantum coherent dynamics in the ground-state subspace of atomic and molecular Λ-systems in the absence of coherent driving.
Gamma-ray bursts (GRBs) are known to have the most relativistic jets, with initial Lorentz factors in the order of a few hundreds. Many GRBs display an early X-ray light-curve plateau, which was not theoretically expected and therefore puzzled the community for many years. Here, we show that this observed signal is naturally obtained within the classical GRB fireball model, provided that the initial Lorentz factor is rather a few tens, and the expansion occurs into a medium-low density wind. The range of Lorentz factors in GRB jets is thus much wider than previously thought and bridges an observational gap between mildly relativistic jets inferred in active galactic nuclei, to highly relativistic jets deduced in few extreme GRBs. Furthermore, long GRB progenitors are either not Wolf-Rayet stars, or the wind properties during the final stellar evolution phase are different than at earlier times. Our model has predictions that can be tested to verify or reject it in the future, such as lack of GeV emission, lack of strong thermal component and long (few seconds) variability during the prompt phase characterizing plateau bursts.
Vocal communication is used across taxa to convey a range of information. One of the most well-studied vocal behaviors is the song of temperate passerine birds. Among individuals, male song differs across numerous acoustic parameters, many of which are used by females to assess male quality. Males in better condition often produce higher song output and start singing earlier in the day compared to other males. However, the energetic cost of singing varies throughout the day and may be affected by the singer’s foraging abilities. Along an elevation gradient, harsher environmental conditions at higher elevations shape foraging abilities in mountain chickadees (Poecile gambeli), which are non-migratory food hoarders. High-elevation mountain chickadees exhibit superior spatial cognitive abilities and a higher propensity to cache food, which enables them to forage more efficiently, compared to lower elevation birds. High-elevation males may therefore be able to produce higher song output, especially earlier in the day, than low-elevation males. We compared the daily singing routines of male mountain chickadees inhabiting high and low elevations. We found no difference in total daily song output between elevations; however, high-elevation males sang significantly more than low-elevation males at dawn, when singing is both crucial for reproductive opportunities and most costly due to overnight fasting. Song output at dawn may therefore act as an indicator of condition in male mountain chickadees. Significance statement Animals communicate across modalities to exchange information about foraging, predators, and movements. Researchers have studied the vocalizations of songbirds to understand how individual variation affects the behavior of receives, particularly regarding male song and female mating preferences. The song of many songbirds is learned locally and contains information about the location of origin and respective selective pressures. We tested whether natural access to food via food cache recovery was associated with daily singing routines in food-caching birds. Singing at dawn is thought to be costly as it follows overnight fasting. We found that birds from harsher environments—where selection for enhanced spatial cognitive abilities required for cache retrieval is much stronger—sing more at dawn compared to males from milder environments, where selection on spatial cognition is relaxed. This work shows that environmental selection pressures affect signal production in male songbirds, which may provide information to females during mate choice.
PurposeTo examine the association between bullying victimization and meeting recommendations for the 24-h movement behaviors of physical activity, screen use, and sleep in adolescents.Methods Participants were a sample of US adolescents from the 2015–2019 national Youth Risk Behavior Survey (N = 43,847; Mean age = 16.0 ± 1.2 years; 50.7% female). The bullying victimization variables included the bullying experiences at school and online. Weighted multivariable logistic regressions analyzed associations between bullying victimization and meeting recommendations for 24-h movement behaviors controlling for age, sex, race/ethnicity, and weight status.ResultsAdolescents meeting non-academic screen and sleep recommendations had 25% (OR = 0.75, 95% CI 0.69–0.82) and 19% (OR = 0.81, 95% CI 0.74–0.89) lower odds to be bullied at school. Adolescents meeting non-academic screen recommendation had 27% lower odds (OR = 0.73, 95% CI 0.58–0.91) of experience online bullying. Male adolescents who met physical activity, non-academic screen use, and sleep recommendations had lower odds of experience the bullying at school of 29% (OR = 0.71, 95% CI 0.59–0.85), 26% (OR = 0.74, 95% CI 0.61–0.90), and 31% (OR = 0.69, 95% CI 0.55–0.86), respectively. Among the females, non-academic screen use was the only movement behavior yielded statistical significance, in that those who met the recommendation had 15% (OR = 0.85, 95% CI 0.73–0.98) lower odds of experience the bullying at school.Conclusion The presence of meeting 24-h movement behavior recommendations associates with a lower probability of bullying at school and online in adolescents. Interestingly, these associations tended to be stronger and more consistent in males compared to females.
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Guy Hoelzer
  • Department of Biology
Gary Haynes
  • Department of Anthropology
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