Simultaneous measurement of phonons and ionization using SiCAD s

Our group at Stanford has configured a double-sided Silicon Crystal Acoustic Detector (SiCAD) for simultaneous measurement of both phonons and ionization. This detector operates at 370mK and consists of Ti Transition Edge Sensors (TES), having microsecond resolution times, patterned on both sides of a 300µm thick Si wafer. Distinguishing an electron-recoil event from a nuclear-recoil event is possible due to the different partitioning of energy into phonons vs. ionization for the two types of event. This is a powerful background rejection technique for neutrino physics experiments and dark matter searches where the events of interest are nuclear-recoils. In addition, the phonon sensor is position sensitive. In particular, it determines the depth of an event and can be used to reject events occurring near the surface. This detector also allows us to refine our recent measurement of the fraction of phonon energy propagating ballistically from nuclear-recoil events¹.     

Crystal growth and investigation of efficient non-linear optical materials in the mixed (2,-4-dinitrophenyl)-L-alanine (DPA) and 2-methyl-4-nitroaniline (MNA) system

When a 11 weight mixture of (2,-4-dinitrophenyl)-L-alanine (DPA) and 2-methyl-4-nitroaniline (MNA) is dissolved in a 5050 volume mixture of ethyl acetate and hexane, two types of crystals were observed on slow evaporation. In the first stage of crystallization, light-yellow plates of MNA measuring up to 25 mm×5 mm×1 mm were formed, which belong to the triclinic space group P1 with lattice parameters a=0.7621 (3) nm, b=0.795 2(5) nm, c=0.8200 (2) nm, =111.84(2)°, = 93.76(2)°, =116.84(3)°, Z=2. The volume of the unit cell containing two molecules is 361.9(1)×10^–3 nm³. The powder SHG efficiency of the triclinic polymorph (MNA(T)) is about the same as that of the monoclinic MNA(M). The Raman spectrum of the new crystal is similar to that of MNA(M) crystallized from the vapour phase or solution, except for the change in the intensity of a few bands. The DSC data show minor differences in the melting points and specific heats for the two phases. The second stage of crystallization resulted in the formation of orange-yellow coloured crystals of the DPA:MNA complex, in the monoclinic space group P2₁ with lattice parameters a =0.6876(1) nm, b=0.7621(3) nm, c=1.7626(4) nm, =96.62(2)°, V=917.5 ×10^–3 nm³, Z=2 for C₁₆H₁₇N₅O₈. The Raman spectrum of DPA:MNA consists of bands from both DPA and MNA. The complex melts at 138(1)°C with a specific heat of 25.3(4) cal g^–1 according to the DSC measurements. The powder SHG efficiency is nearly the same as that of methyl-(2,4-dinitriphenyl)-aminoproanoate (MAP).     

Cerebrospinal fluid flow in the normal and hydrocephalic human brain

Advances in magnetic resonance (MR) imaging techniques enable the accurate measurements of cerebrospinal fluid (CSF) flow in the human brain. In addition, image reconstruction tools facilitate the collection of patient-specific brain geometry data such as the exact dimensions of the ventricular and subarachnoidal spaces (SAS) as well as the computer-aided reconstruction of the CSF-filled spaces. The solution of the conservation of CSF mass and momentum balances over a finite computational mesh obtained from the MR images predict the patients' CSF flow and pressure field. Advanced image reconstruction tools used in conjunction with first principles of fluid mechanics allow an accurate verification of the CSF flow patters for individual patients. This paper presents a detailed analysis of pulsatile CSF flow and pressure dynamics in a normal and hydrocephalic patient. Experimental CSF flow measurements and computational results of flow and pressure fields in the ventricular system, the SAS and brain parenchyma are presented. The pulsating CSF motion is explored in normal and pathological conditions of communicating hydrocephalus. This paper predicts small transmantle pressure differences between lateral ventricles and SASs (approximately 10 Pa). The transmantle pressure between ventricles and SAS remains small even in the hydrocephalic patient (approximately 30 Pa), but the ICP pulsatility increases by a factor of four. The computational fluid dynamics (CFD) results of the predicted CSF flow velocities are in good agreement with Cine MRI measurements. Differences between the predicted and observed CSF flow velocities in the prepontine area point towards complex brain-CSF interactions. The paper presents the complete computational model to predict the pulsatile CSF flow in the cranial cavity.     

Application of dissimilarity indices, principal coordinates analysis, and rank tests to peak tables in metabolomics of the gas chromatography/mass spectrometry of human sweat

The majority of works in metabolomics employ approaches based on principal components analysis (PCA) and partial least-squares, primarily to determine whether samples fall within large groups. However, analytical chemists rarely tackle the problem of individual fingerprinting, and in order to do this effectively, it is necessary to study a large number of small groups rather than a small number of large groups and different approaches are required, as described in this paper. Furthermore, many metabolomic studies on mammals and humans involve analyzing compounds (or peaks) that are present in only a certain portion of samples, and conventional approaches of PCA do not cope well with sparse matrices where there may be many 0s. There is, however, a large number of qualitative similarity measures available for this purpose that can be exploited via principal coordinates analysis (PCO). It can be shown that PCA scores are a specific case of PCO scores, using a quantitative similarity measure. A large-scale study of human sweat consisting of nearly 1000 gas chromatography/mass spectrometry analyses from the sweat of an isolated population of 200 individuals in Carinthia (Southern Austria) sampled once per fortnight over 10 weeks was employed in this study and grouped into families. The first step was to produce a peak table requiring peak detection, alignment, and integration. Peaks were reduced from 5080 to 373 that occurred in at least 1 individual over 4 out of 5 fortnights. Both qualitative (presence/absence) and quantitative (equivalent to PCA) similarity measures can be computed. PCO and the Kolomorogov-Smirnoff (KS) rank test are applied to these similarity matrices. It is shown that for this data set there is a reproducible individual fingerprint, which is best represented using the qualitative similarity measure as assessed both by the Hotelling t2 statistic as applied to PCO scores and the probabilities associated with the KS rank test.     

Zero-Valent Iron: Impact of Anions Present during Synthesis on Subsequent Nanoparticle Reactivity

Zero-valent iron particles are an effective remediation technology for ground water contaminated with halogenated organic compounds. In particular, nanoscale zero-valent iron is a promising material for remediation because of its high specific surface area, which results in faster rate constants and more effective use of the iron. An aspect of iron nanoparticle reactivity that has not been explored is the impact of anions present during iron metal nanoparticle synthesis. Solutions containing chloride, phosphate, sulfate, and nitrate anions and ferric ions were used to generate iron oxide nanoparticles. The resulting materials were dialyzed to remove dissolved by-products and then dried and reduced by hydrogen gas at high temperature. The reactivity of the resulting zero-valent iron nanoparticles was quantified by monitoring the kinetics as well as products of carbon tetrachloride reduction, and significant differences in reactivity and chloroform yield were observed. The reactivity of nanoparticles prepared in the presence of sulfate and phosphate demonstrated the highest reactivity and chloroform yield. Furthermore, substantial variations in the solid-state products of oxidation (magnetite, iron sulfide, goethite, etc.) were also observed.     

Increased sensitivity of acute myeloid leukemias to lovastatin-induced apoptosis: A potential therapeutic approach

We recently demonstrated that 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, the rate-limiting enzyme of de novo cholesterol synthesis, was a potential mediator of the biological effects of retinoic acid on human neuroblastoma cells. The HMG-CoA reductase inhibitor, lovastatin, which is used extensively in the treatment of hypercholesterolemia, induced a potent apoptotic response in human neuroblastoma cells. This apoptotic response was triggered at lower concentrations and occurred more rapidly than had been previously reported in other tumor-derived cell lines, including breast and prostate carcinomas. Because of the increased sensitivity of neuroblastoma cells to lovastatin-induced apoptosis, we examined the effect of this agent on a variety of tumor cells, including leukemic cell lines and primary patient samples. Based on a variety of cytotoxicity and apoptosis assays, the 6 acute lymphocytic leukemia cell lines tested displayed a weak apoptotic response to lovastatin. In contrast, the majority of the acute myeloid leukemic cell lines (6/7) and primary cell cultures (13/22) showed significant sensitivity to lovastatin-induced apoptosis, similar to the neuroblastoma cell response. Of significance, in the acute myeloid leukemia, but not the acute lymphocytic leukemia cell lines, lovastatin-induced cytotoxicity was pronounced even at the physiological relevant concentrations of this agent. Therefore, our study suggests the evaluation of HMG-CoA reductase inhibitors as a therapeutic approach in the treatment of acute myeloid leukemia.     

Rigorous mathematical modeling techniques for optimal delivery of macromolecules to the brain

Several treatment modalities for neurodegenerative diseases or tumors of the central nervous system involve invasive delivery of large molecular weight drugs to the brain. Despite the ample record of experimental studies, accurate drug targeting for the human brain remains a challenge. This paper proposes a systematic design method of administering drugs to specific locations in the human brain based on first principles transport in porous media. The proposed mathematical framework predicts achievable treatment volumes in target regions as a function of brain anatomy and infusion catheter position. A systematic procedure to determine the optimal infusion and catheter design parameters that maximize the penetration depth and volumes of distribution will be discussed. The computer simulations are validated with agarose gel phantom experiments and rat data. The rigorous computational approach will allow physicians and scientists to better plan the administration of therapeutic drugs to the central nervous system.      

Ground terminations of lightning protective systems

In a lightning protective system, the ground terminations must be designed to keep within fixed values the step voltage both inside and outside the protected structure and the maximum total voltage. Design criteria shall take into account that the behavior of ground systems is affected by their length, by soil resistivity, by amplitude and wave shapes of lightning currents. In this paper, investigations carried out on ground terminations when subjected to impulse currents are presented and typical phenomena which characterize their behavior are summarized. Theoretical analysis of the transient phenomenon and new experimental results on each electrode are presented. On the basis of maximum step voltage and of the statistical variation of lightning currents, the design of ground terminations is analyzed and curves for their practical sizing are given. Provisions to avoid discharges into the soil between ground conductors and buried cables or pipes are given, together with computation methods to evaluate overvoltage amplitudes between live conductors and ground in shielded cables     

Lessons from social psychology on discrediting psychiatric stigma.

Advocacy, government, and public-service groups rely on a variety of strategies to diminish the impact of stigma on persons with severe mental illness. These strategies include protest, education, and promoting contact between the general public and persons with these disorders. The authors argue that social psychological research on ethnic minority and other group stereotypes should be considered when implementing these strategies. Such research indicates that (a) attempts to suppress stereotypes through protest can result in a rebound effect; (b) education programs may be limited because many stereotypes are resilient to change; and (c) contact is enhanced in a variety of factors, including equal status, cooperative interaction, and institutional support. Future directions for research and practice to reduce stigma toward persons with severe mental illness are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)