Temperature-dependent optical properties of wurtzite InN

Optical properties and carrier recombination dynamics of a series of InN epilayers, with varying free electron concentrations, grown by molecular beam epitaxy were studied by steady-state photoluminescence (PL) and time-resolved differential transmission spectroscopy. At room temperature strong PL around 0.7 eV was observed. Temperature-dependent PL measurements show a redshift of the peak energy and a linear increase of the emission linewidth with temperature. Furthermore, our results demonstrate that room temperature carrier lifetimes are inversely proportional to the free electron concentrations for theses samples. Carrier lifetime as long as 1.3 ns was observed in the best quality sample, indicating a highly improved crystalline quality.     

Boundary element weight function analysis of a strip yield crack in a rotating disk

The boundary element method combined with subtration of Bueckner singular fields are used to obtain weight functions for an internal edge crack in a rotating annular disk. A previously developed, general representation of the weight function is used which leads to integrals that can be evaluated analytically to obtain the stress intensity factor and surface displacements of the crack. The determination of crack tip opening displacements for the strip yield crack is reduced to a non-singular integral which can be evaluated in closed form. The strip yield zone length and crack tip opening displacement are determined for an internal radial crack in a rotating annular disk for a range of crack lengths and rotational speeds.     

Rare‐Cell Enrichment by a Rapid,Label‐Free,Ultrasonic Isopycnic Technique for Medical Diagnostics

One significant challenge in medical diagnostics lies in the development of label‐free methods to separate different cells within complex biological samples. Here we demonstrate a generic, low‐power ultrasonic separation technique, able to enrich different cell types based upon their physical properties. For malaria, we differentiate between infected and non‐infected red blood cells in a fingerprick‐sized drop of blood. We are able to achieve an enrichment of circulating cells infected by the ring stage of the parasite over nonparasitized red blood cells by between two and three orders of magnitude in less than 3 seconds (enabling detection at parasitemia levels as low as 0.0005 %). In a second example, we also show that our methods can be used to enrich different cell types, concentrating Trypanosoma in blood at very low levels of infection, on disposable, low‐cost chips.     

Jackson's theorem for compact connected Lie groups

We prove that for f ε E = C(G) or L^p(G), 1 p < ∞, where G is any compact connected Lie group, and for n 1, there is a trigonometric polynomial t_n on G of degree n so that f − t_nE C_rω_r(n⁻¹,f). Here ω_r(t, f) denotes the rth modulus of continuity of f. Using this and sharp estimates of the Lebesgue constants recently obtained by Giulini and Travaglini, we obtain “best possible” criteria for the norm convergence of the Fourier series of f.     

Correlations without joint distributions in quantum mechanics

The use of joint distribution functions for noncommuting observables in quantum thermodynamics is investigated in the light of L. Cohen's proof that such distributions are not determined by the quantum state. Cohen's proof is irrelevant to uses of the functions that do not depend on interpreting them as distributions. An example of this, from quantum Onsager theory, is discussed. Other uses presuppose that correlations betweenp andq values depend at least on the state. But correlations may be fixed by the state even though the distribution varies from one ensemble to another represented by that state. Taking covariance as a measure of correlation, it is shown that the different commonly used joint distributions yield the same correlations for a given state. A general characterization is given for a family of distributions with this same covariance.     

Reduction of systems of linear differential equations to jordan normal form

Summary Various methods are discussed of finding a non-singular matrix P such that PAP⁻¹=J, where J is theJordan normal form of A, with special reference to the problem of reducing the system of equations x=Ax to the form y=Jy, where y=Px. To Giovanni Sansone on his 70^th birth day.     

Rare‐Cell Enrichment by a Rapid,Label‐Free,Ultrasonic Isopycnic Technique for Medical Diagnostics

One significant challenge in medical diagnostics lies in the development of label‐free methods to separate different cells within complex biological samples. Here we demonstrate a generic, low‐power ultrasonic separation technique, able to enrich different cell types based upon their physical properties. For malaria, we differentiate between infected and non‐infected red blood cells in a fingerprick‐sized drop of blood. We are able to achieve an enrichment of circulating cells infected by the ring stage of the parasite over nonparasitized red blood cells by between two and three orders of magnitude in less than 3 seconds (enabling detection at parasitemia levels as low as 0.0005 %). In a second example, we also show that our methods can be used to enrich different cell types, concentrating Trypanosoma in blood at very low levels of infection, on disposable, low‐cost chips.