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.
Mitigating invasive annual grass impacts is critical to halting native rangeland conversion to fire-prone, annual grass-dominated communities and maintaining the ecosystem services provided by perennial plants. The herbicide indaziflam (Rejuvra, Bayer, Leverkusen, Germany) may allow managers to selectively deplete annual grass seed banks in plant communities that continue to support desirable perennial vegetation, but nontarget impacts are difficult to assess in the small plots typically used in herbicide trials, and the potential for impacts to the seed bank is not well understood. To assess the potential for nontarget impacts resulting from indaziflam treatment, we used modified-Whittaker multiscale vegetation plots to compare diversity (species accumulation) in three treatment plots (73 g ai ha⁻¹ indaziflam) and three control plots in sagebrush-grasslands near Pinedale, Wyoming that are invaded by cheatgrass (Bromus tectorum L.). We also assessed the density and richness of shallow (0- to 1-cm depth) and deep (1- to 5-cm depth) germinable seed banks in treatment and control plots by tracking seedling emergence from seed bank samples during a 20-wk greenhouse study. Vegetation data and seed bank samples were collected during the third growing season after treatment. Treatment did not impact aboveground species diversity, but this contrasted with the results of the seed bank assay; shallow and deep native seed bank density and shallow native seed bank richness were significantly reduced in treatment plots. All impacted species were detected in the aboveground plant community in treatment plots after herbicide application, suggesting that reduced native annual abundance may be temporary. Considering the potential for nontarget impacts to seed banks will help land managers accurately assess trade-offs when making treatment decisions.
The present work reports the utilization of laser treatment for the structuring of a B2O3 coating on ceramic substrates. The two ceramic substrates, pure Al2O3, and Al2O3-20wt% B2O3, were prepared in-house using cold pressing and sintering route. The coatings were prepared by applying the ethanol-B2O3 slurry on the ceramic substrate using a dip coater followed by drying at 100 °C. The dried coatings were subjected to the continuous laser at 22, 29, and 36 W of laser power to achieve the final coating. Coating characterization by X-ray diffraction (XRD) revealed the importance of laser power on controlling the phases of B2O3, which are H3BO3, HBO2, and amorphous B2O3. The crystallinity index (CI) of the coatings calculated using XRD spectrum decreased with an increase in laser power. The coating processed at 36 W showed the lowest CI that reveals higher amorphous B2O3 content. Sliding tests conducted in a controlled humid environment at three sliding velocities suggested a direct relationship between tribological performance and CI value—coating with lower CI value provided consistent lower COF. Additionally, a strong influence of the substrate on tribological performance was also observed—the coatings on the Al2O3-20wt%B2O3 substrate performed superior compared to the coating on the pure Al2O3. The effect of substrates is discussed in terms of thermal conductivity to achieve higher amorphous B2O3 content and the initial surface roughness of the substrates.
Infections by maternally inherited bacterial endosymbionts, especially Wolbachia , are common in insects and other invertebrates but infection dynamics across species ranges are largely under studied. Specifically, we lack a broad understanding of the origin of Wolbachia infections in novel hosts and the factors governing their spread. We used Genotype-by-Sequencing (GBS) data from previous population genomics studies for range-wide surveys of Wolbachia presence and genetic diversity in over 2,700 North American butterflies of the genus Lycaeides . As few as one sequence read identified by assembly to a Wolbachia pan-reference genome provided high accuracy in detecting infections as determined by confirmatory PCR tests. Using a conservative threshold of five reads, we detected Wolbachia in all but two of the 107 sampling localities spanning the continent, and with most localities having high infection frequencies (mean = 91\% infection rate). Three major lineages of Wolbachia were identified as separate strains that appear to represent three separate invasions of Lycaeides butterflies. Overall, we found extensive evidence for acquisition of Wolbachia through interspecific transfer between host lineages. Strain wLyc C was confined to a single butterfly taxon, hybrid lineages derived from it, and closely adjacent populations in other taxa. While the other two strains were detected throughout the rest of the continent, strain wLyc B almost always co-occurred with wLyc A. Our demographic modeling suggests wLyc B is a recent invasion. These results demonstrate the utility of using resequencing data from hosts to quantify Wolbachia genetic variation and provide evidence of multiple colonizations of novel hosts through hybridization between butterfly lineages and complex dynamics between Wolbachia strains.
Strongly deformed footwall rocks exposed in metamorphic core complexes (MCC) of the North American Cordillera were exhumed via ductile attenuation, mylonitic shearing, and detachment faulting. Whether these structures accommodated diapiric upwelling or regional extension via low-angle normal faulting is debated. The Ruby Mountains-East Humboldt Range MCC, northeast Nevada, records top-west normal-sense exhumation of deformed Proterozoic-Paleozoic stratigraphy and older basement. We conducted 1:24,000-scale mapping of the southwestern East Humboldt Range, with integrated structural, geochemical, and geochronological analyses to characterize the geometry and kinematics of extension and exhumation of the mylonitized footwall. Bedrock stratigraphy is pervasively intruded by Cretaceous, Eocene, and Oligocene intrusions, but observations of a coherent stratigraphic section show >80% vertical attenuation of Neoproterozoic to Ordovician rocks. These rocks are penetratively sheared with top-west kinematics. The shear zone thus experienced combined pure- and simple-shear (i.e., general shear) strain. We argue that this shear zone was syn-/post-kinematic with respect to Oligocene plutonism because: (1) mylonitic shearing spatially corresponds with preceding Oligocene intrusions; (2) thermochronology reveal that the shear zone experienced substantial cooling and exhumation after Oligocene plutonism; and (3) the mylonites are crosscut by undated, but likely late Oligocene, leucogranite. We propose that Eocene mantle-derived magmatism and thermal incubation led to Oligocene diapiric upwelling of the middle crust, with ductile stretching focused on the flanks of this upwarp. Regional Basin and Range extension initiated later in the middle Miocene. Therefore, the development of the East Humboldt Range shear zone was not driven by regional extension and coupled detachment faulting.
Background and Objectives: Understanding the influence of social resources on health is crucial in gerontological research. However, access to social resources may differ by one’s particular LGBT identity and the intersection of LGBT identity with other sociodemographic characteristics, including age. Research Design and Methods: Using 2010 data from Caring and Aging With Pride (N = 2,536), this study examined how access to social resources varied by LGBT identity and whether the effect of LGBT identity was modified by additional sociodemographic characteristics among LGBT adults aged 50 to 95. Results: Lesbian respondents had larger social networks than gay male respondents, and gay male respondents had smaller networks than transgender respondents. Lesbian respondents reported more social support and community belonging than other identity groups. Bisexual male respondents and transgender respondents had less support than gay male respondents, and bisexual male respondents reported less community belonging than gay male respondents. Age and education moderated the association between LGBT identity and social support. Discussion and Implications: This study demonstrated differences in access to social resources according to environmental circumstances that can intersect and govern access to social resources. Findings highlight the importance of considering social support separately from social network size; thus, large social networks do not necessarily provide ample social support. LGBT older adults had different perceptions of social support than their middle-aged counterparts. Health and human service professionals should not only consider the sexual and gender identity of their LGBT clients, but also education and age when assessing access to social resources.
To predict hydrologic responses to inputs and perturbations, it is important to understand how precipitation is stored in catchments, released back to the atmosphere via evapotranspiration (ET), or transported to aquifers and streams. We investigated this partitioning of precipitation using stable isotopes of water (18O) at the Can Vila catchment in the Spanish Pyrenees mountains. The isotope data covered four years of measurements, comprising >550 rainfall and >980 stream water samples, capturing intra-event variations. They were complemented by fortnightly plant water isotope data sampled over eight months. The isotope data were used to quantify how long it takes for water to become evapotranspiration or to be discharged as streamflow using StorAge Selection (SAS) functions. We calibrated the SAS functions using a conventional approach fitting the model solely to stream water isotope data and a multi-objective calibration approach in which the model was simultaneously fitted to tree xylem water isotope data. Our results showed that the conventional model-fitting approach was not able to constrain the model parameters that represented the age of water supplying ET. Consequently, the ET isotope ratios simulated by the conventionally calibrated model failed to adequately simulate the observed xylem isotope ratios. However, the SAS model was capable of adequately simulating both observed stream water and xylem water isotope ratios, if those xylem water isotope observations were used in calibration (i.e., the multi-objective approach). The multi-objective calibration approach led to a more constrained parameter space facilitating parameter value identification. The model was tested on a segment of data reserved for validation showing a Kling–Gupta Efficiency of 0.72 compared to the 0.83 observed during in the calibration period. The water-age dynamics inferred from the model calibrated using the conventional approach differed substantially from those inferred from the multi-objective calibration model. The latter suggested that the median ages of water supplying evapotranspiration is much older (150–300 d) than what was suggested by the former (50–200 d). Regardless, the modeling results support recent findings in ecohydrological field studies that highlighted both subsurface heterogeneity of water storage and fluxes and the use of relatively old water by trees. We contextualized the SAS-derived water ages by also using young-water-fraction and endmember-splitting approaches, which respectively also showed the contribution of young water to streamflow was variable but sensitive to runoff rates and that ET was largely sourced by winter precipitation that must have resided in the subsurface across seasons.
Prison officers not only affect prison operations, but correctional workplace variables also have effects on officers. Most of the past empirical research on this topic has focused on officers working in Western prisons. This study used the job demands–resources model to examine the effects of workplace variables in terms of job demands (e.g., perceived dangerousness of the job and role overload) and job resources (e.g., job autonomy, job variety, instrumental communication, and quality supervision) on job involvement among Indian prison officers using a sample of 163 prison officers from a prison in the state of Haryana in India. OLS regression indicated role overload, job autonomy, and instrumental communication all had nonsignificant effects, while job variety and quality supervision had positive effects on job involvement, as did the job demand of perceived dangerousness of the job. Similar to past research, the positive effects of job variety and quality supervision appear to be universal across prisons, as are the lack of direct effects for role overload and instrumental communication. Conversely, the effects of perceived dangerousness of the job and job autonomy appear to be contextual, varying across prisons in different nations.
Melioidosis is very challenging to diagnose. There is a clear need for a point-of-care assay for the detection of B. pseudomallei antigen directly from patient samples.
Unlike the other terrestrial planets, Earth has a substantial silica-rich continental crust with a bulk andesitic composition. A small number of meteorites with andesitic bulk compositions have been identified that are thought to be the products of partial melting of chondritic protoliths, a mode of petrogenesis distinct from that of Earth’s continental crust. Here we show, using geochemical analyses, that unlike other known andesitic meteorites, Erg Chech 002 has strongly fractionated and low abundances of the highly siderophile elements and mineralogy consistent with origin from a melt. The meteorite’s bulk composition, which is similar to terrestrial andesites, cannot be explained by partial melting of basaltic lithologies and instead requires a metal-free chondritic source. We argue that Erg Chech 002 probably formed by ~15–25% melting of the mantle of an alkali-undepleted differentiated asteroid. Our findings suggest that extensive silicate differentiation after metal–silicate equilibration of chondritic parent bodies was already occurring within the first 2.25 million years of Solar System history and that andesitic crust formation does not necessarily require plate tectonics.
Understanding bacterial communication mechanisms is imperative to improve our current understanding of bacterial infectivity and find alternatives to current modes of antibacterial therapeutics. Both Gram-positive and Gram-negative bacteria use quorum sensing (QS) to regulate group behaviours and associated phenotypes in a cell-density-dependent manner. Group behaviours, phenotypic expression and resultant infection and disease can largely be attributed to efficient bacterial communication. Of particular interest are the communication mechanisms of Gram-positive bacteria known as streptococci. This group has demonstrated marked resistance to traditional antibiotic treatment, resulting in increased morbidity and mortality of infected hosts and an ever-increasing burden on the healthcare system. Modulating circuits and mechanisms involved in streptococcal communication has proven to be a promising anti-virulence therapeutic approach that allows managing bacterial phenotypic response but does not affect bacterial viability. Targeting the chemical signals bacteria use for communication is a promising starting point, as manipulation of these signals can dramatically affect resultant bacterial phenotypes, minimizing associated morbidity and mortality. This review will focus on the use of modified peptide signals in modulating the development of proliferative phenotypes in different streptococcal species, specifically regarding how such modification can attenuate bacterial infectivity and aid in developing future alternative therapeutic agents.
Traffic signal coordination, which connects a series of signals along an arterial by various coordination methodologies, has been proven as one of the most cost-effective means for alleviating traffic congestion. Various metropolitan planning organizations (MPO) or transportation management centers (TMC) have included signal timing updates in their strategic plans. However, in practice, signal coordination is usually implemented when traffic volume is heavy (i.e., during peak hours). For the rest of the day, the free operation strategy is usually used to reduce the waiting time of uncoordinated phases. However, this free operation strategy may result in the loss of operational efficiency on the major street. Currently, implementing signal coordination during off-peak hours is rare in the U.S. since there is lack of an efficient method that considers traffic operations for both the major and the minor streets. Therefore, this research provides a novel method that balances the control delays between the major street and the minor street. The procedure is to optimize the splits of the major street while also using the reservice strategy in the signal controller for the minor street. Microsimulation modeling was employed to assess the performance of traffic signal coordination during off-peak periods. Results show that, under reasonable splits, the coordination effect on the major street can be achieved and protected with an acceptable delay to minor street traffic. The strategy can be immediately implemented to reduce travel time for major street traffic.
To address the mounting concern about the validity of student self-reported data, this study relies on official matriculation records to gauge the effect of classroom diversity on student dropout risk. Using panel data to track the 4-year dropout risk of a cohort of new first-year students (N = 3545) at a public research university, we employ a discrete-time-to-event history model to estimate the marginal effect of classroom ethnic-racial composition while controlling for both time-variant and time-invariant student-level and classroom-level factors on demographics, precollege preparation, college academic experience, campus living arrangement, and financial aid support. The study finds: 1) The effect of classroom ethnic-racial composition during a student’s enrollment spell varies across student ethnic-racial identity, first-generation status, and level of academic preparation of classroom peers; exposure to Asian classmates is associated with a lower dropout risk for Black students, while exposure to underrepresented minority classmates (excluding Asians) is associated with lower dropout risk for Hispanic, Native American, multi-ethic, and first-generation students. 2) Semester-to-semester rise in exposure to Asian classmates is associated with a lower dropout risk for Black students. 3) Observed effects of classroom ethnic-racial composition do not vary significantly with enrollment in diversity-focused courses. 4) Estimated effect sizes of ethnic-racial classroom composition are very small in comparison to effects of student academic engagement and success. Thus, the nexus between diversity and academic persistence is moderated by a host of factors, both time variant and invariant, and is difficult to leverage operationally due to observed small effects and student discretionary behavior.
Graphene is an attractive material for many applications due to excellent inherent properties such as lower density, high mechanical strength, higher thermal conductivity, etc. However, it has been used as an additive material due to size limitation. To overcome the size limitation without affecting the inherent properties of 2D graphene sheets, researchers have developed graphene aerogel (GA) by different synthesis techniques. GA has become an emerging light-weight structure in the group of aerogel materials because of various applications. In this review article, the mechanical properties of GA have been discussed by considering the structural parameters of GA, such as pore size, graphene sheet alignments, and wall thickness, because the mechanical performance of the GA is an important criterion prior to its application in any field. It has also been highlighted that the structural parameters can be altered during synthesis to achieve desired mechanical properties. Applications of GA have been thoroughly discussed in the field of polymer composites and how GA-polymer structures can help to generate a cleaner environment by separating spilled oil from water and removing organic pollutants from water. In addition, potential of GA for various other applications with suitable nano material additives have been highlighted.
Governments, utilities, and energy companies are increasingly looking towards energy storage technologies to extend the availability of variable renewable power sources such as solar and wind. In this Perspective, we examine these fast-shifting developments by mapping and analyzing landscapes of renewable energy storage emerging across the Western United States. We focus on the rollout of several interrelated leading technologies: utility-scale lithium-ion batteries, supported by increasing regional lithium mining, and proposals for new pumped storage hydropower. Drawing on critical resource geography, we examine energy storage as both a component of renewable transition and as its own driver of landscape transformation, resource extraction, and conflict. By mapping and interpreting emerging Western landscapes, we show that leading energy storage technologies and the materials needed to make them can require extensive surficial land use and have significant regional water impacts, and that they are generating opposition from groups concerned about environmental degradation and (in)justice. We propose an agenda for future research on energy storage aimed at rendering its development more socio-ecologically beneficial and just.
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Guy Hoelzer
  • Department of Biology
Gary Haynes
  • Department of Anthropology
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