Inter-dependence of the volume and stress ensembles and equipartition in statistical mechanics of granular systems

We discuss the statistical mechanics of granular matter and derive several significant results. First, we show that, contrary to common belief, the volume and stress ensembles are inter-dependent, necessitating the use of both. We use the combined ensemble to calculate explicitly expectation values of structural and stress-related quantities for two-dimensional systems. We thence demonstrate that structural properties may depend on the angoricity tensor and that stress-based quantities may depend on the compactivity. This calls into question previous statistical mechanical analyses of static granular systems and related derivations of expectation values. Second, we establish the existence of an intriguing equipartition principle - the total volume is shared equally amongst both structural and stress-related degrees of freedom. Third, we derive an expression for the compactivity that makes it possible to quantify it from macroscopic measurements.Comment: 5 pages, including 2 figures, To appear in Phys. Rev. Let

Da Vinci Fluids, catch-up dynamics and dense granular flow

We introduce and study a da Vinci Fluid, a fluid whose dissipation is dominated by solid friction. We analyse the flow rheology of a discrete model and then coarse-grain it to the continuum. We find that the model gives rise to behaviour that is characteristic of dense granular fluids. In particular, it leads to plug flow. We analyse the nucleation mechanism of plugs and their development. We find that plug boundaries generically expand and we calculate the growth rate of plug regions. In systems whose internal effective friction coefficient is relatively uniform we find that the linear size of plug regions grows as (time)$^{1/3}$. The suitability of the model to granular materials is discussed.Comment: 5 pages, 3 figures, edited for clarifications and added reference

Schematics of a Water Balloon Launcher Design and Reproducible Water-Balloon-Filling Procedures Used for a Middle School Summer Science Camp

We recently held a Science Summer Camp for middle school students, designed to infuse young people with increased excitement for STEM (Science, Technology, Engineering, and Math) subjects. Our efforts, which received nationally-syndicated news coverage,1 included the invention of a versatile water balloon launcher. This document contains: (1) detailed construction schematics and user operation guidelines for our balloon launcher; (2) data and instructions for reproducibly filling water balloons to specific volumes and weights, within used by students during the summer camp

High Cancer Burden Among Antiretroviral Therapy Users in Malawi: a Record Linkage Study of Observational HIV Cohorts and Cancer Registry Data.

Background With antiretroviral therapy (ART), AIDS-defining cancer incidence has declined and non-AIDS defining cancers are now more frequent among HIV-infected populations in high-income countries. In sub-Saharan Africa, limited epidemiological data describe cancer burden among ART users. Methods We used probabilistic algorithms to link cases from the population-based cancer registry with electronic medical records supporting ART delivery in the Malawi's two largest HIV cohorts, Lighthouse Trust (LT; 2007-2010) and Queen Elizabeth Central Hospital (QECH; 2000-2010). Age-adjusted cancer incidence rates (IR) and 95% confidence intervals were estimated by cancer site, early versus late incidence periods (4 -24 and >24 months after ART start), and WHO stage among naïve ART initiators enrolled for at least 90 days. Results We identified 4,346 cancers among 28,576 persons. Most people initiated ART at advanced WHO stage (LT stage 3/4: 55%; QECH stage 3/4: 66%); 12% of patients had prevalent malignancies at ART initiation, which were predominantly AIDS-defining eligibility criteria for initiating ART. Kaposi sarcoma (KS) had the highest IR (634.7 per 100,000 person-years), followed by cervical cancer (36.6). KS incidence was highest during the early period 4-24 months after ART initiation. Non-AIDS defining cancers (NADC) accounted for 6% of new cancers. Conclusions Under historical ART guidelines, NADC were observed at low rates, and were eclipsed by high KS and cervical cancer burden. Cancer burden among Malawian ART users does not yet mirror high-income countries. Integrated cancer screening and management in HIV clinics, especially for KS and cervical cancer, remain important priorities in the current Malawi context