Institutional Repository

The UDSpace Institutional Repository collects and disseminates research material from the University of Delaware.

  • Faculty, staff, and graduate students can deposit their research material directly into UDSpace. Faculty may use UDSpace to fulfill the University of Delaware Faculty Senate Open Access Resolution, and in many cases may use it to fulfill open access requirements from grant funding agencies.
  • Departments can use UDSpace to publish or distribute their working papers, technical reports, or other research material.
  • UDSpace also includes all doctoral dissertations from winter 2014 forward, and all master's theses from fall 2009 forward.

To learn more about UDSpace, and how you can make your research openly accessible to the public, visit our UDSpace Policies website.


Recent Submissions

Analysis of neutron monitor count rates and timing distributions from latitude surveys
(Journal of Physics: Conference Series, 2023-12-01) Yakum, P.; Khamphakdee, S.; Nuntiyakul, W.; Sáiz, A.; Ruffolo, D.; Evenson, P.; Bangliang, C.; Seripienlert, A.; Jiang, P.; Chuanraksasat, P.
Neutron monitors continuously record the hadronic part of secondary atmospheric radiation on the ground, which originates from primary cosmic rays. In Thailand, we developed a mobile neutron monitor housed inside a standard-size shipping container named "Changvan." It contains three neutron-sensitive proportional counters set up in the typical NM64 layout. However, the central counter doesn't have the lead producer, leading us to refer to it as a "semi-leaded" neutron monitor. We examined cosmic ray spectral variations on two latitude surveys during 2018-2019 and 2019-2020. This work examines the ratio of count rates between leaded and unleaded setups, which shows notable variation based on geomagnetic cutoff rigidity, suggesting a sensitivity to the cosmic ray spectrum. This measurement could be implemented at stationary stations. The unleaded counter, shielded by the reflector with a higher count from nearby lead, may have advantages over a bare one. Furthermore, we explore alternative techniques to identify spectral changes in Galactic cosmic rays using Changvan data. We analyze using time delay histograms to determine the leader fraction (L) of neutrons that are not preceded by another neutron from the same primary cosmic ray. We also examine other parameters, including the alpha (α) parameter and pulse rate (PR), which can be compared with count rates (CR). Our findings indicate that the ratios of L and α are not significantly affected by geomagnetic cutoff rigidity. In contrast, CR and PR exhibit significant dependency and show opposite trends.
Monte Carlo Simulation and measurement of Calibration Neutron Monitor count rate dependence on proximity to water
(Journal of Physics: Conference Series, 2023-12-01) Duangjai, B.; Nuntiyakul, W.; Seripienlert, A.; Pagwhan, A.; Chaiwongkhot, K.; Sáiz, A.; Ruffolo, D.; Evenson, P.
Due to their global availability, neutron monitors play a crucial role in measuring time variations in the Galactic cosmic ray flux. A portable calibration neutron monitor (CalMon) is useful for intercalibrating various neutron monitors to ensure accurate measurements. A common technique to ensure that the calibration is done in a consistent environment is to place the CalMon at some height above a wide container (such as a portable swimming pool) filled with water. This study investigates the impact of CalMon height and water depth on the count rate ratio relative to a standard 18NM64 count rate recorded nearby (CalMon/18NM64). We compare simulated data from the FLUKA Monte Carlo package to experimental data from [1] to demonstrate the statistical accuracy of our simulation. Using the simulation results, we then extend the study of the proximity-to-water effect on the counting rate. In this work, we present a preliminary empirical model by analyzing the CalMon/18NM64 as a function of CalMon to water distance. Overall, our study enhances understanding of the response of calibration monitors (now often called "mini-neutron monitors") operated in various locations worldwide, and validates the Monte Carlo techniques used to model the response of the global neutron monitor network.
Pulse selection algorithm for NM64 neutron detector
(Journal of Physics: Conference Series, 2023-12-01) Kittiya, A.; Nuntiyakul, W.; Chaiwongkhot, K.; Sáiz, A.; Ruffolo, D.; Seripienlert, A.; Evenson, P.
We propose an algorithm to sepearate pile-up pulses in neutron detectors by utilizing a standard pulse. For this method to be effective, the data must consist mostly of isolated pulses. First, we define a reference pulse by averaging a sample of clearly isolated pulses. Then, for an arbitrary signal, we calculate a shape deviation by summing up the squared residuals between it and the reference pulse. The pulse with the greatest shape deviation is removed from the process. We then recalculate the reference pulse and repeat until the remaining pulses have shape deviation within a threshold. These remaining pulses exhibit a very good linear trend between area and height, allowing us to screen those suspected as pile-ups. A pulse much higher than the final reference pulse, despite being in the area-height-trend and having low shape deviation, is considered a pile-up of two identical pulses. The final reference pulse is fitted to a function defined by two pieces of Gaussian-multiplied polynomial, normalized, and called the standard pulse. We attempted to fit the pile-up pulse with one standard pulse to separate pile-up pulses. If the sum of squared normalized residuals is higher than some threshold, we add one more pulse, try fitting again, and repeat up to three pulses. We apply this algorithm to the pulses collected from one counter at the Princess Sirindhorn Neutron Monitor station at the summit of Doi Inthanon Mountain, Chiang Mai, Thailand, measured by an oscilloscope. The algorithm correctly separates obvious pile-up cases, allowing to record individual pulse timing with improved accuracy. However, we found small pulses, usually belong to gamma rays, that blend with neutron pulse and pass 100 mV output filtration. After removing those under 100 mV, the pulse area distribution of the separated pile-up is consistent with that of single pulses except at very small pulse sizes.
Got (clean) milk? Organization, incentives, and management in Indian dairy cooperatives
(Journal of Economic Behavior and Organization, 2023-08) Rao, Manaswini; Shenoy, Ashish
Smallholder producers in developing countries often collaborate in teams that take advantage of scale economies and allocate surplus among members. We experimentally evaluate team-level incentive contracts for quality upgrading among Indian dairy cooperatives where there is a risk of free-riding because individual quality cannot be traced. Incentives improve aggregate quality, with evidence of increased effort from both producers and cooperative managers. However, several managers decline incentive payments when they cannot control how payment information is disclosed to cooperative members. Survey evidence indicates publicity lowers managerial returns, suggesting transparency-based efforts to constrain elites can undermine the core policy goal.
Melatonin supplementation does not alter vascular function or oxidative stress in healthy normotensive adults on a high sodium diet
(Physiological Reports, 2023-12-18) Ramos Gonzalez, Macarena; Axler, Michael R.; Kaseman, Kathryn E.; Lobene, Andrea J.; Farquhar, William B.; Witman, Melissa A.; Kirkman, Danielle L.; Lennon, Shannon L.
High sodium diets (HSD) can cause vascular dysfunction, in part due to increases in reactive oxygen species (ROS). Melatonin reduces ROS in healthy and clinical populations and may improve vascular function. The purpose was to determine the effect of melatonin supplementation on vascular function and ROS during 10 days of a HSD. We hypothesized that melatonin supplementation during a HSD would improve vascular function and decrease ROS levels compared to HSD alone. Twenty-seven participants (13 M/14 W, 26.7 ± 2.9 years, BMI: 23.6 ± 2.0 kg/m2, BP: 110 ± 9/67 ± 7 mmHg) were randomized to a 10-day HSD (6900 mg sodium/d) supplemented with either 10 mg of melatonin (HSD + MEL) or a placebo (HSD + PL) daily. Brachial artery flow-mediated dilation, a measure of macrovascular function, (HSD + PL: 7.1 ± 3.8%; HSD + MEL: 6.7 ± 3.4%; p = 0.59) and tissue oxygenation index (TSI) reperfusion rate, a measure of microvascular reactivity, (HSD + PL: 0.21 ± 0.06%/s; HSD + MEL: 0.21 ± 0.08%/s; p = 0.97) and TSI area under the curve (HSD + PL: 199899 ± 10,863 a.u.; HSD + MEL: 20315 ± 11,348 a.u.; p = 0.17) were similar at the end of each condition. Neither nitroxide molarity (HSD + PL: 7.8 × 10−5 ± 4.1 × 10−5 mol/L; HSD + MEL: 8.7 × 10−5 ± 5.1 × 10−5 mol/L; p = 0.55) nor free radical number (HSD + PL: 8.0 × 1015 ± 4.4 × 1015; HSD + MEL: 9.0 × 1015 ± 4.9 × 1015; p = 0.51) were different between conditions. Melatonin supplementation did not alter vascular function or ROS levels while on a HSD in this sample of young healthy