Mass coupling and Q−1ofimpurity−limitednormalQ^{-1} of impurity-limited normal ^3$He in a torsion pendulum

We present results of the $Q^{-1}$ and period shift, $\Delta P$, for $^3$He confined in a 98% nominal open aerogel on a torsion pendulum. The aerogel is compressed uniaxially by 10% along a direction aligned to the torsion pendulum axis and was grown within a 400 $\mu$m tall pancake (after compression) similar to an Andronikashvili geometry. The result is a high $Q$ pendulum able to resolve $Q^{-1}$ and mass coupling of the impurity-limited $^3$He over the whole temperature range. After measuring the empty cell background, we filled the cell above the critical point and observe a temperature dependent period shift, $\Delta P$, between 100 mK and 3 mK that is 2.9$$ of the period shift (after filling) at 100 mK. The $Q^{-1}$ due to the $^3$He decreases by an order of magnitude between 100 mK and 3 mK at a pressure of $0.14\pm0.03$ bar. We compare the observable quantities to the corresponding calculated $Q^{-1}$ and period shift for bulk $^3$He.Comment: 8 pages, 3 figure

Applications of Dynamic Modeling and Statistical Analysis to Infectious Diseases

In this dissertation, I explore the disproportionate burden of infectious disease outbreaks, epidemics, and pandemics and the projected impact of interventions for mitigating their harm on populations in Cameroon and the United States. The spatial heterogeneity in vaccination coverage and access to care in Cameroon creates areas that are highly susceptible to measles transmission. In the US, the HIV epidemic is increasingly concentrated in the southern states in addition to larger cities with variable levels of prevention and linkage to sustained treatment. Disparities in COVID-19 burden exist by race and geography across Michigan, in part due to systemic racism and underlying health burdens.In Chapter One, I model the spatiotemporal dynamics of a large outbreak of measles in Cameroon by using several multivariate time-series models at the health district, department, and region levels. By assessing the spatiotemporal dynamics at different geographical scales, it was possible to determine the respective contribution of each administrative division to measles transmission throughout the country. The model including long-distance population mobility optimally reflected the spatial spread of measles. Population movement between departments within regions was estimated to contribute to 9.1% of all cases and movement between regions contributed to 18.1% of cases at the health district level. These findings demonstrate the need to improve our understanding of the roles of population mobility and local heterogeneity of vaccination coverage in the spread and control of measles in Cameroon. In Chapter Two, I develop a mathematical model of HIV transmission and progression to evaluate the impact of expanding HIV prevention, diagnosis, treatment, and viral suppression levels in 57 priority counties and states in the United States, as identified by the federal government initiative “Ending the HIV Epidemic”. This plan aims to increase access to diagnosis, linkage to treatment, maintenance of treatment and pre-exposure prophylaxis uptake in high-incidence counties as well as states with high burdens of disease in rural areas between 2020 and 2030. I project that the number of annual new infections could be reduced by 58% and that over 157,000 cumulative new infectious could be averted over the next decade nationwide upon successful implementation of this initiative. Despite the substantial benefit incurred by this HIV care continuum expansion, additional concerted efforts beyond its scope such as community-specific interventions benefiting disproportionately affected populations, stigma erasure, HIV criminalization elimination, and ending systemic oppression will be needed to truly stop HIV transmission in the US. In Chapter Three, I examined racial disparities in COVID-19 mortality in Michigan, US, stratified by age, sex, and comorbidity prevalence. Using individual-level linked death certificate and surveillance data on all COVID-19 deaths statewide, I calculated that the mortality rate for Black populations overall was 3.6 times that of White populations, with heterogeneity across neighbourhoods. Strikingly, the mortality rate for Black individuals under 65 years lacking comorbidities was 12.6 times that of their White counterparts. Prevalence of comorbidities, age, and sex did not account for the elevated mortality rate experienced by Black individuals in Michigan. Even after accounting for demographic and underlying health characteristics, my work highlights that disparities across race resulting from systemic racism are compounded in crises. This dissertation contributes to our understanding of the inequitable impacts of epidemics on under-resourced or historically marginalized communities within the United States and Cameroon, with analyses focused on racial and geographic disparities. Addressing the root causes of these disparities through elimination of systemic racism, improved access to care, and healthcare reform is necessary to prevent further infections and deaths. Furthermore, these changes have the capacity to reduce the impact of future infectious disease epidemics on the populations that are consistently and disproportionately affected

WASEP model in improving access to water and sanitation in Pakistan: an example in best practices

Post-2015, as global leaders move towards SDGs, it is important for countries in the Global South to situate water and sanitation interventions not simply as ‘ends’, but also as ‘means’ towards achieving broader goals of human development. The paper demonstrates this, firstly, by discussing theoretical debates in secondary data to situate the importance of water and sanitation in human development, and secondly, by using primary data (pre-and-post intervention analysis) from the case study of Water and Sanitation Extension Programme (WASEP) which has successfully applied an integrated model for provision of safe water and sanitation, along with a behavioural change communication strategy for improved health and hygiene practices in the mountainous regions of Pakistan. Drawing from the learning of WASEP approach, the paper concludes that policymakers in the Global South should re-conceptualize WASH interventions to account for issues of community empowerment, WASH sustainability, and the regional/national human development goals

Extension of the HF program to partially filled f-subshells

A new version of a Hartree-Fock program is presented that includes extensions for partially filled f-subshells. The program allows the calculation of term dependent Hartree-Fock orbitals and energies in LS coupling for configurations with no more than two open subshells, including f-subshells

Pure spin-angular momentum coefficients for non-scalar one-particle operators in jj-coupling

A revised program for generating the spin-angular coefficients in relativistic atomic structure calculations is presented. When compared with our previous version [G.Gaigalas, S.Fritzsche and I.P.Grant, CPC 139 (2001) 263], the new version of the Anco program now provides these coefficients for both, scalar as well as non-scalar one-particle operators as they arise frequently in the study of transition probabilities, photoionization and electron capture processes, the alignment transfer through excited atomic states, collision strengths, and in many other investigations. The program is based on a recently developed formalism [G.Gaigalas, Z.Rudzikas, and C.F.Fischer, J. Phys. B 30 (1997) 3747], which combines techniques from second quantization in coupled tensorial form, the theory of quasispin, and the use of reduced coefficients of fractional parentage, in order to derive the spin-angular coefficients for complex atomic shell structures more efficiently. By making this approach now available also for non-scalar interactions, therefore, studies on a whole field of new properties and processes are likely to become possible even for atoms and ions with a complex structure

Detection of DNA and Poly-L-Lysine using CVD Graphene-channel FET Biosensors

A graphene channel field-effect biosensor is demonstrated for detecting the binding of double-stranded DNA and poly-l-lysine. Sensors consist of CVD graphene transferred using a clean, etchant-free transfer method. The presence of DNA and poly-l-lysine are detected by the conductance change of the graphene transistor. A readily measured shift in the Dirac Voltage (the voltage at which the graphenes resistance peaks) is observed after the graphene channel is exposed to solutions containing DNA or poly-l-lysine. The Dirac voltage shift is attributed to the binding/unbinding of charged molecules on the graphene surface. The polarity of the response changes to positive direction with poly-l-lysine and negative direction with DNA. This response results in detection limits of 8 pM for 48.5 kbp DNA and 11 pM for poly-l-lysine. The biosensors are easy to fabricate, reusable and are promising as sensors of a wide variety of charged biomolecule

Low-power photothermal self-oscillation of bimetallic nanowires

We investigate the nonlinear mechanics of a bimetallic, optically absorbing SiN-Nb nanowire in the presence of incident laser light and a reflecting Si mirror. Situated in a standing wave of optical intensity and subject to photothermal forces, the nanowire undergoes self-induced oscillations at low incident light thresholds of $<1\, \rm{\mu W}$ due to engineered strong temperature-position ($T$-$z$) coupling. Along with inducing self-oscillation, laser light causes large changes to the mechanical resonant frequency $\omega_0$ and equilibrium position $z_0$ that cannot be neglected. We present experimental results and a theoretical model for the motion under laser illumination. In the model, we solve the governing nonlinear differential equations by perturbative means to show that self-oscillation amplitude is set by the competing effects of direct $T$-$z$ coupling and $2\omega_0$ parametric excitation due to $T$-$\omega_0$ coupling. We then study the linearized equations of motion to show that the optimal thermal time constant $\tau$ for photothermal feedback is $\tau \to \infty$ rather than the widely reported $\omega_0 \tau = 1$. Lastly, we demonstrate photothermal quality factor ($Q$) enhancement of driven motion as a means to counteract air damping. Understanding photothermal effects on micromechanical devices, as well as nonlinear aspects of optics-based motion detection, can enable new device applications as oscillators or other electronic elements with smaller device footprints and less stringent ambient vacuum requirements.Comment: New references adde

Low temperature acoustic properties of amorphous silica and the Tunneling Model

Internal friction and speed of sound of a-SiO(2) was measured above 6 mK using a torsional oscillator at 90 kHz, controlling for thermal decoupling, non-linear effects, and clamping losses. Strain amplitudes e(A) = 10^{-8} mark the transition between the linear and non-linear regime. In the linear regime, excellent agreement with the Tunneling Model was observed for both the internal friction and speed of sound, with a cut-off energy of E(min) = 6.6 mK. In the non-linear regime, two different behaviors were observed. Above 10 mK the behavior was typical for non-linear harmonic oscillators, while below 10 mK a different behavior was found. Its origin is not understood.Comment: 1 tex file, 6 figure

Dissipation signatures of the normal and superfluid phases in torsion pendulum experiments with 3He in aerogel

We present data for energy dissipation factor (Q^{-1}) over a broad temperature range at various pressures of a torsion pendulum setup used to study 3He confined in a 98% open silica aerogel. Values for Q^{-1} above T_c are temperature independent and have a weak pressure dependence. Below T_c, a deliberate axial compression of the aerogel by 10% widens the range of metastability for a superfluid Equal Spin Pairing (ESP) state; we observe this ESP phase on cooling and the B phase on warming over an extended temperature region. While the dissipation for the B phase tends to zero as T goes to 0, Q^{-1} exhibits a peak value greater than that at T_c at intermediate temperatures. Values for Q^{-1} in the ESP phase are consistently higher than in the B phase and are proportional to \rho_s/\rho until the ESP to B phase transition is attained. We apply a viscoelastic collision-drag model, which couples the motion of the helium and the aerogel through a frictional relaxation time \tau_f. Our dissipation data is not sensitive to the damping due to the presumed small but non-zero value of \tau_f. The result is that an additional mechanism to dissipate energy not captured in the collision-drag model and related to the emergence of the superfluid order must exist. The extra dissipation below T_c is possibly associated with mutual friction between the superfluid phases and the clamped normal fluid. The pressure dependence of the measured dissipation in both superfluid phases is likely related to the pressure dependence of the gap structure of the "dirty" superfluid. The large dissipation in the ESP state is consistent with the phase being the A or the Polar with the order parameter nodes oriented in the plane of the cell and perpendicular to the aerogel anisotropy axis.Comment: 12 pages, 7 figure