PASP: A high voltage array experiment

In the near future, Air Force mission payloads will require significant increases in power. Sophisticated sensing systems such as infrared focal plane detector arrays and radar will be employed by the Air Force to fulfill its strategic objectives. These payloads will demand that the power subsystem provide up to 50 kW at the end of mission life, more than an order of magnitude greater than is currently required. Some of these payloads must be flown in low-Earth polar orbits to satisfy mission objectives, and it is likely that large (500 to 600 sq m) solar photovoltaic arrays will operate in the low-Earth polar environment. The standard 28 volt power subsystem is not weight efficient for the array power levels being considered. The impact of the solar array operating voltage on the total weight of the array and the subsystem power conditioning and distribution components is illustrated. In the interest of reducing power subsystem weight, higher array operating voltages are considered. The problems which the higher array voltage present to the array designer are discussed. In order to provide a maximum return on the tremendous investment of resources required to develop and place these assets in orbit, they must be designed to operate effectively for extended periods of time. To achieve this, the system must be able to function in the threat-induced and natural space environment

Tension in secretory granule membranes causes extensive membrane transfer through the exocytotic fusion pore

or fusion to occur the repulsive forces between two interacting phospholipid bilayers must be reduced. In model systems, this can be achieved by increasing the surface tension of at least one of the membranes. However, there has so far been no evidence that the secretory granule membrane is under tension. We have been studying exocytosis by using the patch-clamp technique to measure the surface area of the plasma membrane of degranulating mast cells. When a secretory granule fuses with the plasma membrane there is a step increase in the cell surface area. Some fusion events are reversible, in which case we have found that the backstep is larger than the initial step, indicating that there is a net decrease in the area of the plasma membrane. The decrease has the following properties: (i) the magnitude is strongly dependent on the lifetime of the fusion event and can be extensive, representing as much as 40% of the initial granule surface area; (ii) the rate of decrease is independent of granule size; and (iii) the decrease is not dependent on swelling of the secretory granule matrix. We conclude that the granule membrane is under tension and that this tension causes a net transfer of membrane from the plasma membrane to the secretory granule, while they are connected by the fusion pore. The high membrane tension in the secretory granule may be the critical stress necessary for bringing about exocytotic fusion.National Institutes of Health GM-3885

Communications Biophysics

Contains reports on six research projects.National Science Foundation (Grant G-16526)National Institutes of Health (Grant MH-04737-02

Absent otoacoustic emissions predict otitis media in young Aboriginal children: A birth cohort study in Aboriginal and non-Aboriginal children in an arid zone of Western Australia

AbstractBackground: Otitis media (OM) is the most common paediatric illness for which antibiotics areprescribed. In Australian Aboriginal children OM is frequently asymptomatic and starts at a youngerage, is more common and more likely to result in hearing loss than in non-Aboriginal children.Absent transient evoked otoacoustic emissions (TEOAEs) may predict subsequent risk of OM.Methods: 100 Aboriginal and 180 non-Aboriginal children in a semi-arid zone of WesternAustralia were followed regularly from birth to age 2 years. Tympanometry was conducted atroutine field follow-up from age 3 months. Routine clinical examination by an ENT specialist wasto be done 3 times and hearing assessment by an audiologist twice. TEOAEs were measured at ages<1 and 1–2 months. Cox proportional hazards model was used to investigate the associationbetween absent TEOAEs and subsequent risk of OM.Results: At routine ENT specialist clinics, OM was detected in 55% of 184 examinations inAboriginal children and 26% of 392 examinations in non-Aboriginal children; peak prevalence was72% at age 5–9 months in Aboriginal children and 40% at 10–14 months in non-Aboriginal children.Moderate-severe hearing loss was present in 32% of 47 Aboriginal children and 7% of 120 non-Aboriginal children aged 12 months or more.TEOAE responses were present in 90% (46/51) of Aboriginal children and 99% (120/121) of non-Aboriginal children aged <1 month and in 62% (21/34) and 93% (108/116), respectively, inAboriginal and non-Aboriginal children at age 1–2 months. Aboriginal children who failed TEOAEat age 1–2 months were 2.6 times more likely to develop OM subsequently than those who passed.Overall prevalence of type B tympanograms at field follow-up was 50% (n = 78) in Aboriginalchildren and 20% (n = 95) in non-Aboriginal children

Single-channel properties of a stretch-sensitive chloride channel in the human mast cell line HMC-1

A stretch-activated (SA) Cl− channel in the plasma membrane of the human mast cell line HMC-1 was identified in outside-out patch-clamp experiments. SA currents, induced by pressure applied to the pipette, exhibited voltage dependence with strong outward rectification (55.1 pS at +100 mV and an about tenfold lower conductance at −100 mV). The probability of the SA channel being open (Po) also showed steep outward rectification and pressure dependence. The open-time distribution was fitted with three components with time constants of τ1o = 755.1 ms, τ2o = 166.4 ms, and τ3o = 16.5 ms at +60 mV. The closed-time distribution also required three components with time constants of τ1c = 661.6 ms, τ2c = 253.2 ms, and τ3c = 5.6 ms at +60 mV. Lowering extracellular Cl− concentration reduced the conductance, shifted the reversal potential toward chloride reversal potential, and decreased the Po at positive potentials. The SA Cl− currents were reversibly blocked by the chloride channel blocker 4,4′-diisothiocyanatostilbene-2,2′-disulfonic acid (DIDS) but not by (Z)-1-(p-dimethylaminoethoxyphenyl)-1,2-diphenyl-1-butene (tamoxifen). Furthermore, in HMC-1 cells swelling due to osmotic stress, DIDS could inhibit the increase in intracellular [Ca2+] and degranulation. We conclude that in the HMC-1 cell line, the SA outward currents are mediated by Cl− influx. The SA Cl− channel might contribute to mast cell degranulation caused by mechanical stimuli or accelerate membrane fusion during the degranulation process

Business networks and localization effects for new Swedish technology-based firms’ innovation performance

This study examines the business networks and localization effects for new technology-based firms (NTBFs) in the context of innovation performance (the number of patents and product differentiation). In this regard, the study includes 28 variables. A survey was conducted in 2016 with 401 Swedish NTBFs that were small and young (the employment mean was 1.80 and the average age of each firm was 28.3\ua0months). The biggest category of NTBFs was knowledge-intensive high-technology services, followed by medium high-technology manufacturing, and high-technology manufacturing. Hypotheses on how business networks and localization are related to innovation performance were tested using principal component analysis, correlation analysis, and regression analysis. The results show that the primary significant factor for innovation performance regarding business networks and localization dimensions are professional network services, while industrial and regional areas also have a positive relationship on product differentiation. Our study also shows that innovation performance enhances firms’ abilities to access external financing through professional network services (e.g., venture capital companies)

Sheddable Coatings for Long-Circulating Nanoparticles

Nanoparticles, such as liposomes, polymeric micelles, lipoplexes and polyplexes are frequently studied as targeted drug carrier systems. The ability of these particles to circulate in the bloodstream for a prolonged period of time is often a prerequisite for successful targeted delivery. To achieve this, hydrophilic ‘stealth’ polymers, such as poly(ethylene glycol) (PEG), are used as coating materials. Such polymers shield the particle surface and thereby reduce opsonization by blood proteins and uptake by macrophages of the mononuclear phagocyte system. Yet, after localizing in the pathological site, nanoparticles should deliver their contents in an efficient manner to achieve a sufficient therapeutic response. The polymer coating, however, may hinder drug release and target cell interaction and can therefore be an obstacle in the realization of the therapeutic response. Attempts have been made to enhance the therapeutic efficacy of sterically stabilized nanoparticles by means of shedding, i.e. a loss of the coating after arrival at the target site. Such an ‘unmasking’ process may facilitate drug release and/or target cell interaction processes. This review presents an overview of the literature regarding different shedding strategies that have been investigated for the preparation of sterically stabilized nanoparticulates. Detach mechanisms and stimuli that have been used are described

Spatial Distribution of Ca(2+) Signals during Repetitive Depolarizing Stimuli in Adrenal Chromaffin Cells

Exocytosis in adrenal chromaffin cells is strongly influenced by the pattern of stimulation. To understand the dynamic and spatial properties of the underlying Ca(2+) signal, we used pulsed laser Ca(2+) imaging to capture Ca(2+) gradients during stimulation by single and repetitive depolarizing stimuli. Short single pulses (10–100 ms) lead to the development of submembrane Ca(2+) gradients, as previously described (F. D. Marengo and J. R. Monck, 2000, Biophysical Journal, 79:1800–1820). Repetitive stimulation with trains of multiple pulses (50 ms each, 2Hz) produce a pattern of intracellular Ca(2+) increase that progressively changes from the typical Ca(2+) gradient seen after a single pulse to a Ca(2+) increase throughout the cell that peaks at values 3–4 times higher than the maximum values obtained at the end of single pulses. After seven or more pulses, the fluorescence increase was typically larger in the interior of the cell than in the submembrane region. The pattern of Ca(2+) gradient was not modified by inhibitors of Ca(2+)-induced Ca(2+) release (ryanodine), inhibitors of IP(3)-induced Ca(2+) release (xestospongin), or treatments designed to deplete intracellular Ca(2+) stores (thapsigargin). However, we found that the large fluorescence increase in the cell interior spatially colocalized with the nucleus. These results can be simulated using mathematical models of Ca(2+) redistribution in which the nucleus takes up Ca(2+) by active or passive transport mechanisms. These results show that chromaffin cells can respond to depolarizing stimuli with different dynamic Ca(2+) signals in the submembrane space, the cytosol, and the nucleus