Low Particle Number Research Articles

Shell-model Monte Carlo simulations of the BCS-BEC crossover in few-fermion systems

Frankfurt Institute for Advanced Studies, D-60438 Frankfurt, Germany(Dated: July 23, 2009)We study a trapped system of fermions with a zero-range two-body interaction using the shell-model Monte Carlo method, providing ab initio results for the low particle number limit wheremean-field theory is not applicable. We present results for the N-body energies as function ofinteraction strength, particle number, and temperature. The subtle question of renormalization ina finite model space is addressed and the convergence of our method and its applicability acrossthe BCS-BEC crossover is discussed. Our findings indicate that very good quantitative results canbe obtained on the BCS side, whereas at unitarity and in the BEC regime the convergence is lessclear. Comparison to N = 2 analytics at zero and finite temperature, and to other calculations inthe literature for N > 2 show very good agreement.

Tissue distribution of 20 nm, 100 nm and 1000 nm fluorescent polystyrene latex nanospheres following acute systemic or acute and repeat airway exposure in the rat

Understanding tissue distribution and clearance of nanomaterials following different routes of exposure is needed for risk assessment. F344 female rats received single or multiple exposures to 20 nm, 100 nm or 1000 nm latex fluorospheres by intravenous (i.v.) injection or oral pharyngeal aspiration into the airways. The presence of fluorospheres in tissues was assessed up to 90–120 days after the final dose. Blood, perfusion fluid, bone marrow, brain, eyes, feces, gut, heart, kidney, liver, lung, muscle, skin, spleen, thymus, tongue, urine and uterus plus ovaries were collected for analysis. Liver, spleen and lung were the greatest tissue depots for all particles following i.v. injection. The proportion of 100 nm and 1000 nm but not 20 nm spheres significantly increased in the spleen over time. Lung was the greatest tissue depot for all particles following single or repeat airway exposure. Greater than 95% of 1000 nm spheres that were recovered were in the lung in contrast to 70–80% of 20 nm spheres or 89–95% of 100 nm spheres. All 3 sizes were found in gut or gut + feces 1–7 days after lung exposure. The thymus was the largest extra-pulmonary depot for the particles; up to 25% of recovered 20 nm particles were in the thymus up to 4 months after exposure compared to 6% of 100 nm particles and 1–3% of 1000 nm particles. A small proportion of 20 nm particles were detected in kidney following both acute and repeat airway exposure. Low numbers of particles were found in the circulation (blood, perfusion), bone marrow, brain, heart, liver and spleen but not in eye, muscle, skin, tongue, ovaries, uterus or urine. These data show that the tissue targets of nano- and micron-sized spheres are very similar whether exposure occurs systemically or via the airways while the proportion of particles in some tissues and tissue clearance varies based on particle size.

Protein Assembly onto Cationic Supported Bilayers

Cationic supported bilayers on latex are useful to isolate and immobilize oppositely charged proteins as a monomolecular layer over a range of low protein concentrations and particle number densities. Cholera toxin (CT) from Vibrio cholerae, an 87 kDa AB5 hexameric protein and bovine serum albumin (BSA) self-assembled on dioctadecyldimethylammonium bromide (DODAB) supported bilayers with high affinity yielding highly organized and monodisperse particulates at 5 x 10(9) particles/mL, over a range of low protein concentrations (0-0.025 mg/mL BSA or CT). Protein association onto the bilayer-covered polystyrene sulfate (PSS) was determined from adsorption isotherms, dynamic light scattering for size distributions and zeta-potential analysis revealing a monomolecular, thin and highly organized protein layer surrounding each particle with potential for biospecific recognition such as antigen-antibody, receptor-ligand, hybridization of oligonucleotide sequences, all of them important in immunodiagnosis, selective biomolecular chromatographic separations, microarrays design and others.

SIMULATION OF SYMMETRIC NUCLEI AND THE ROLE OF PAULI POTENTIAL IN BINDING ENERGIES AND RADII

It is shown that the use of a density-dependent effective Pauli potential together with a generic nucleon–nucleon interaction potential plays a crucial role to reproduce not only the binding energies but also the matter root mean square radii of medium mass range spin–isospin saturated nuclei. This study is performed with a semiclassical Monte Carlo many-body simulation within the context of a simplified nucleon–nucleon interaction to focus on the effect of the genuine correlations due to the fermionic nature of nucleons. The procedure obtained is rather robust and it does not depend on the detailed features of the nucleon–nucleon interaction. For nuclei below saturation the density dependence may be represented in terms either of the nucleon number, A, or the associated Fermi momenta. When testing the simulation procedure for idealized "infinite" symmetric nuclear matter within the corresponding range of densities, we find that, beyond the low particle number limit, finite size effects do not affect the Pauli potential strength parametrization.

Automated SEM/EDS Analysis of Airbag Residue. II: Airbag Residue as a Source of Percussion Primer Residue Particles

Automated scanning electron microscopy with energy dispersive spectroscopy has been used to analyze airbag residue particles. Analysis of airbag residue from some passenger side airbags revealed some residue particles which are consistent with gunshot residue (GSR) samples. The source of these particles was determined to be percussion primers used to initiate the chemical reaction for deployment. This article identifies some vehicles which contain this type of airbag and demonstrates the types of particles which could be misidentified as being GSR. The low numbers of GSR particles in among the large particle populations of zirconium and/or copper-cobalt particles, which are clearly airbag residue, allow the trained analysts to distinguish the correct source of this residue. Particles containing high aluminum levels, elevated levels of allowable elements in GSR particles, or the presence of elements that are rare in GSR particles stand out as indications that the particles are not GSR in origin. This study serves as a guide to analysts who perform particle analysis in forensic investigations.

Histo-Blood Group Antigen Assay for Detecting Noroviruses in Water

We evaluated a novel, magnetic-bead-based histo-blood group antigen assay for the recovery of low numbers of norovirus particles. Using this assay, with Norwalk virus seeded in environmental waters as a model, we were able to recover 30 to 300 genomic copies of the virus.

Measuring aerosol size distributions with the fast integrated mobility spectrometer

A fast integrated mobility spectrometer (FIMS) has been developed for rapid aerosol size distribution measurements including those aerosols with low particle number concentrations. In this work, an inversion routine has been developed for the FIMS and it is demonstrated that the FIMS can accurately measure aerosol size distributions. The inversion routine includes corrections for the particle residence time in the FIMS and other factors related to the width of the response (or transfer) function and multiple charging of particles. Steady-state size distributions measured with the FIMS compared well with those measured by a scanning mobility particle sizer (SMPS). Experiments also show that the FIMS is able to capture the size distribution of rapidly changing aerosol populations. The total particle concentration integrated from distributions measured by the FIMS agrees well with simultaneous measurements by a condensation particle counter (CPC).

Variability of Particle Number Emissions from Diesel and Hybrid Diesel−Electric Buses in Real Driving Conditions

A linear mixed model was developed to quantify the variability of particle number emissions from transit buses tested in real-world driving conditions. Two conventional diesel buses and two hybrid diesel-electric buses were tested throughout 2004 under different aftertreatments, fuels, drivers, and bus routes. The mixed model controlled the confounding influence of factors inherent to on-board testing. Statistical tests showed that particle number emissions varied significantly according to the after treatment, bus route, driver, bus type, and daily temperature, with only minor variability attributable to differences between fuel types. The daily setup and operation of the sampling equipment (electrical low pressure impactor) and mini-dilution system contributed to 30-84% of the total random variability of particle measurements among tests with diesel oxidation catalysts. By controlling for the sampling day variability, the model better defined the differences in particle emissions among bus routes. In contrast, the low particle number emissions measured with diesel particle filters (decreased by over 99%) did not vary according to operating conditions or bus type but did vary substantially with ambient temperature.

AAV Vector-mediated Reversal of Hypoglycemia in Canine and Murine Glycogen Storage Disease Type Ia

Glycogen storage disease type Ia (GSD-Ia) profoundly impairs glucose release by the liver due to glucose-6-phosphatase (G6Pase) deficiency. An adeno-associated virus (AAV) containing a small human G6Pase transgene was pseudotyped with AAV8 (AAV2/8) to optimize liver tropism. Survival was prolonged in 2-week-old G6Pase (-/-) mice by 600-fold fewer AAV2/8 vector particles (vp), in comparison to previous experiments involving this model (2 x 10(9) vp; 3 x 10(11) vp/kg). When the vector was pseudotyped with AAV1, survival was prolonged only at a higher dose (3 x 10(13) vp/kg). The AAV2/8 vector uniquely prevented hypoglycemia during fasting and fully corrected liver G6Pase deficiency in GSD-Ia mice and dogs. The AAV2/8 vector has prolonged survival in three GSD-Ia dogs to >11 months, which validated this strategy in the large animal model for GSD-Ia. Urinary biomarkers, including lactate and 3-hydroxybutyrate, were corrected by G6Pase expression solely in the liver. Glycogen accumulation in the liver was reduced almost to the normal level in vector-treated GSD-Ia mice and dogs, as was the hepatocyte growth factor (HGF) in GSD-Ia mice. These preclinical data demonstrated the efficacy of correcting hepatic G6Pase deficiency, and support the further preclinical development of AAV vector-mediated gene therapy for GSD-Ia.

Effect of ventilation design on removal of particles in woodturning workstations

Wood processing tasks such as circular sawing and turning that is associated with woodturning operators produce particularly high exposure levels. A computational model including a humanoid and lathe within a test chamber was simulated with monodisperse particles under five different ventilation designs with the aim of reducing the particle suspension within the breathing zone. A commercial CFD code was used to solve the governing equations of motion with a k– ε RNG turbulence model. A discrete Lagrangian model was used to track the particles individually. Measurements to evaluate the efficiency of each ventilation design included total particle clearance and the percentage of particles crossing through the breathing plane. It was concluded that the percentage of particles that cross the breathing plane is of greater significance than the other measurements as it provides a better determination of exposure levels. Ventilation that emanated from the roof and had an angled outlet provided greatest total particle clearance and a low number of particles in the breathing plane. It was also found that the obstruction from the local roof ventilations caused separation of the air that flowed along the ceiling to produce a complex flow region. This study provides a basis for further investigation into the effects of particle size and density on the particle flow patterns and potential inhalation conditions for a given ventilation design.

Effects Of Polystyrene Particle Density on Type II Pneumocytes

Inhalation of small particles is associated with respiratory diseases. The aim of the present study was to investigate the role of ultrafine particle number on lung cells and to describe the effects due to phagocytosis of particles by the cells. A549 cells were treated with 1000, 5000, and 10,000 polystyrene particles and incubated at 37„aC for periods of 24, 48, and 72 hours. Cellular viability and damage were determined on the treated cells and compared with untreated controls. The lung cells were also observed microscopically to assess cell damage. Lung cells exposed for 24 hours with 1,000 and 5,000 particles showed the greatest increase in cell number. Cellular protein levels were similar for all groups (p> 0.05) for the duration of the study. MDA levels for treated groups at 24 and 72 hours were not statistically different from the control groups. Cells treated at 48 hours with 5,000 and 10,000 particles showed increased in the MDA levels above low particle number and control treated groups. Morphological evaluation of the cells revealed increased inclusions with increasing dose. The results from this study indicate the ability of A549 cells to respond to a challenge with ultrafine particles. The concentrations tested caused an initial stimulation cell proliferation at 24 hours followed by increased damage at 48 hours. Future studies will focus on the inflammatory products formed by ingestion of the ultrafine particles.

Feasibility study of particle filters for mobile station receivers

The application of an equalisation method for mobile station terminals using particle filters is presented. To use particle filters for equalisation, a mathematical model is shown which allows the transmitted symbols to be represented as the state of a stochastic system, which can be estimated by particle filters. The authors propose an equaliser structure with particle filters for application in mobile station receivers, especially for GSM/EDGE (Global System for Mobile Communications/Enhanced Data Rate for GSM Evolution). Several improvement strategies, which help to obtain better estimation results with a lower number of particles, are discussed. In addition, performance evaluations of the particle filter equaliser for GSM/EDGE are presented.

Surgical smoke and ultrafine particles

BackgroundElectrocautery, laser tissue ablation, and ultrasonic scalpel tissue dissection all generate a 'surgical smoke' containing ultrafine (<100 nm) and accumulation mode particles (< 1 μm). Epidemiological and toxicological studies have shown that exposure to particulate air pollution is associated with adverse cardiovascular and respiratory health effects.MethodsTo measure the amount of generated particulates in 'surgical smoke' during different surgical procedures and to quantify the particle number concentration for operation room personnel a condensation particle counter (CPC, model 3007, TSI Inc.) was applied.ResultsElectro-cauterization and argon plasma tissue coagulation induced the production of very high number concentration (> 100000 cm-3) of particles in the diameter range of 10 nm to 1 μm. The peak concentration was confined to the immediate local surrounding of the production side. In the presence of a very efficient air conditioning system the increment and decrement of ultrafine particle occurrence was a matter of seconds, with accumulation of lower particle number concentrations in the operation room for only a few minutes.ConclusionOur investigation showed a short term very high exposure to ultrafine particles for surgeons and close assisting operating personnel – alternating with longer periods of low exposure.

Enhanced Response to Enzyme Replacement Therapy in Pompe Disease after the Induction of Immune Tolerance

Pompe disease, which results from mutations in the gene encoding the glycogen-degrading lysosomal enzyme acid alpha -glucosidase (GAA) (also called "acid maltase"), causes death in early childhood related to glycogen accumulation in striated muscle and an accompanying infantile-onset cardiomyopathy. The efficacy of enzyme replacement therapy (ERT) with recombinant human GAA was demonstrated during clinical trials that prolonged subjects' overall survival, prolonged ventilator-free survival, and also improved cardiomyopathy, which led to broad-label approval by the U.S. Food and Drug Administration. Patients who lack any residual GAA expression and are deemed negative for cross-reacting immunologic material (CRIM) have a poor response to ERT. We previously showed that gene therapy with an adeno-associated virus (AAV) vector containing a liver-specific promoter elevated the GAA activity in plasma and prevented anti-GAA antibody formation in immunocompetent GAA-knockout mice for 18 wk, predicting that liver-specific expression of human GAA with the AAV vector would induce immune tolerance and enhance the efficacy of ERT. In this study, a very low number of AAV vector particles was administered before initiation of ERT, to prevent the antibody response in GAA-knockout mice. A robust antibody response was provoked in naive GAA-knockout mice by 6 wk after a challenge with human GAA and Freund's adjuvant; in contrast, administration of the AAV vector before the GAA challenge prevented the antibody response. Most compellingly, the antibody response was prevented by AAV vector administration during the 12 wk of ERT, and the efficacy of ERT was thereby enhanced. Thus, AAV vector-mediated gene therapy induced a tolerance to introduced GAA, and this strategy could enhance the efficacy of ERT in CRIM-negative patients with Pompe disease and in patients with other lysosomal storage diseases.

A comparison of lipid and lipoprotein measurements in the fasting and nonfasting states in patients with type 2 diabetes

ABSTRACTBackground: Patients with diabetes often do not reach recommended lipid targets. This may be in part due to the difficulty of obtaining fasting measurements.Objective: To compare fasting and nonfasting low density lipoprotein cholesterol (LDLc), non-high density lipoprotein cholesterol (non-HDLc), and low density lipoprotein particle number (LDLP) patients with type 2 diabetes (T2DM) and to determine the effect on assessing treatment success.Research design and methods: Standard lipids and NMR lipoproteins were analyzed at baseline and following a standardized meal in patients with T2DM.Outcomes measures: Primary outcomes were agree­ment between fasting and nonfasting LDLc, non-HDLc, and LDLP and the agreement between these measures for determining fasting LDLc treatment success. Direct LDL cholesterol (DLDL) was a secondary outcome.Results: Of 31 patients, only 56% of LDLc measure­ments were equivalent in the fasting and nonfasting states, compared to 97% of DLDLc ( p < 0.0001), 94% of non-HDLc ( p < 0.001) and 77% of LDLP ( p < 0.01) measurements. Assessment of nonfasting lipid values would have resulted in misclassification by treatment target in 15% of LDLc, 3.2% of DLDLc assessments ( p < 0.05 vs. LDLc), and 0% of non-HDLc and LDLP assess­ments ( p < 0.01 vs. LDLc). Nonfasting LDLc, non-HDLc, LDLP, and DLDLc correctly identified fasting LDLc classification in 23/27 (85%), 26/30 (87%, p = NS vs. nonfasting LDLc), 16/30 (53%, p < 0.001 vs. nonfasting LDLc), and 24/30 (80%, p = NS vs. nonfasting LDLc), respectively.Conclusions: If confirmed in larger studies, nonfasting non-HDLc may be a suitable proxy for fasting LDLc in patients with T2DM.

MEDOR, a didactic tool to support interpretation of bioassay data after internal contamination by actinides

A didactic software, MEthodes DOsimètriques de REférence (MEDOR), is being developed to provide help in the interpretation of biological data. Its main purpose is to evaluate the pertinence of the application of different models. This paper describes its first version that is focused on inhalation exposure to actinide aerosols. With this tool, sensitivity analysis on different parameters of the ICRP models can be easily done for aerosol deposition, in terms of activity and particle number, actinide biokinetics and doses. The user can analyse different inhalation cases showing either that dose per unit intake cannot be applied if the aerosol contains a low number of particles or that an inhibition of the late pulmonary clearance by particle transport can occur which contributes to a 3-4 fold increase in effective dose as compared with application of default parameters. This underlines the need to estimate systematically the number of deposited particles, as well as to do chest monitoring as long as possible.

Limits of DPUI application associated with the number of particles within actinide aerosols

Dose per unit intake (DPUI) of radionuclides is obtained using International Commission on Radiological Protection (ICRP) models. After inhalation exposure, the first model calculates the fraction of activity deposited within the different regions of the respiratory tract, assuming that the aerosol contains an infinite number of particles. Using default parameters for workers, an exposure to one annual limit of intake (ALI) corresponds to an aerosol of 239PuO2 containing approximately 1 x 10(6) particles. To reach such an exposure, very low particle number might be involved especially for compounds having a high specific activity. This study provides examples of exposures to actinide aerosols for which the number of particles is too low for a standard application of the ICRP model. These examples, which involve physical studies of aerosols collected at the workplace and interpretation of bioassay data, show that the number of particles of the aerosol can be the main limit for the application of DPUI after inhalation exposure.

Gunshot Residue in Chicago Police Vehicles and Facilities: An Empirical Study

Suspects in shooting investigations in Chicago are routinely transported in department vehicles and detained in department facilities prior to gunshot residue (GSR) evidence collection. The GSR test results are used to associate the suspect with primary exposure to GSR. The potential for these vehicles and facilities being sources of secondary GSR contamination needed to be determined. A total of 201 samples were collected from randomly selected vehicles and detention facilities. The sampling collected trace materials from surfaces that suspects' hands may contact during the arrest process. These samples were examined for the presence of GSR particles using scanning electron microscopy. Upon completion of the automated analysis, those particles that met an initial GSR screening criterion were relocated and reanalyzed. The locations where GSR particles were recovered allowed us to make recommendations to the Chicago Police Department with regard to transporting and detaining these suspects. The low number of GSR particles recovered suggests that the potential for secondary contamination, although present, is relatively low.

Survival of Mycobacterium avium , Legionella pneumophila , Escherichia coli , and Caliciviruses in Drinking Water-Associated Biofilms Grown under High-Shear Turbulent Flow

Most of the bacteria in drinking water distribution systems are associated with biofilms. In biofilms, their nutrient supply is better than in water, and biofilms can provide shelter against disinfection. We used a Propella biofilm reactor for studying the survival of Mycobacterium avium, Legionella pneumophila, Escherichia coli, and canine calicivirus (CaCV) (as a surrogate for human norovirus) in drinking water biofilms grown under high-shear turbulent-flow conditions. The numbers of M. avium and L. pneumophila were analyzed with both culture methods and with peptide nucleic acid fluorescence in situ hybridization (FISH) methods. Even though the numbers of pathogens in biofilms decreased during the experiments, M. avium and L. pneumophila survived in biofilms for more than 2 to 4 weeks in culturable forms. CaCV was detectable with a reverse transcription-PCR method in biofilms for more than 3 weeks. E. coli was detectable by culture for only 4 days in biofilms and 8 days in water, suggesting that it is a poor indicator of the presence of certain waterborne pathogens. With L. pneumophila and M. avium, culture methods underestimated the numbers of bacteria present compared to the FISH results. This study clearly proved that pathogenic bacteria entering water distribution systems can survive in biofilms for at least several weeks, even under conditions of high-shear turbulent flow, and may be a risk to water consumers. Also, considering the low number of virus particles needed to result in an infection, their extended survival in biofilms must be taken into account as a risk for the consumer.

Construction of Point Process Adaptive Filter Algorithms for Neural Systems Using Sequential Monte Carlo Methods

The stochastic state point process filter (SSPPF) and steepest descent point process filter (SDPPF) are adaptive filter algorithms for state estimation from point process observations that have been used to track neural receptive field plasticity and to decode the representations of biological signals in ensemble neural spiking activity. The SSPPF and SDPPF are constructed using, respectively, Gaussian and steepest descent approximations to the standard Bayes and Chapman-Kolmogorov (BCK) system of filter equations. To extend these approaches for constructing point process adaptive filters, we develop sequential Monte Carlo (SMC) approximations to the BCK equations in which the SSPPF and SDPPF serve as the proposal densities. We term the two new SMC point process filters SMC-PPFs and SMC-PPFD, respectively. We illustrate the new filter algorithms by decoding the wind stimulus magnitude from simulated neural spiking activity in the cricket cercal system. The SMC-PPFs and SMC-PPFD provide more accurate state estimates at low number of particles than a conventional bootstrap SMC filter algorithm in which the state transition probability density is the proposal density. We also use the SMC-PPFs algorithm to track the temporal evolution of a spatial receptive field of a rat hippocampal neuron recorded while the animal foraged in an open environment. Our results suggest an approach for constructing point process adaptive filters using SMC methods.