Distribution by Scientific Domains
Distribution within Medical Sciences

Kinds of Barriers

  • access barrier
  • activation barrier
  • activation energy barrier
  • additional barrier
  • anthropogenic barrier
  • biggest barrier
  • biogeographic barrier
  • biogeographical barrier
  • biological barrier
  • blood brain barrier
  • blood-brain barrier
  • brain barrier
  • cell barrier
  • cellular barrier
  • common barrier
  • communication barrier
  • cord barrier
  • cost barrier
  • cultural barrier
  • dielectric barrier
  • different barrier
  • diffusion barrier
  • dispersal barrier
  • ecological barrier
  • economic barrier
  • effective barrier
  • efficient barrier
  • endothelial barrier
  • energy barrier
  • entry barrier
  • epidermal barrier
  • epithelial barrier
  • existing barrier
  • external barrier
  • filtration barrier
  • financial barrier
  • formidable barrier
  • free energy barrier
  • gas barrier
  • genetic barrier
  • geographic barrier
  • geographical barrier
  • geological barrier
  • greatest barrier
  • hard tissue barrier
  • high barrier
  • high energy barrier
  • identified barrier
  • implementation barrier
  • important barrier
  • injection barrier
  • institutional barrier
  • interconversion barrier
  • interconversion energy barrier
  • intestinal barrier
  • isolating barrier
  • key barrier
  • kinetic barrier
  • language barrier
  • legal barrier
  • low barrier
  • low energy barrier
  • main barrier
  • major barrier
  • many barrier
  • mechanical barrier
  • migration barrier
  • mucosal barrier
  • multiple barrier
  • natural barrier
  • organizational barrier
  • orographic barrier
  • other barrier
  • overcoming barrier
  • oxygen barrier
  • perceived barrier
  • permeability barrier
  • permeable reactive barrier
  • physical barrier
  • placental barrier
  • possible barrier
  • potential barrier
  • primary barrier
  • protective barrier
  • psychological barrier
  • reaction barrier
  • reactive barrier
  • reproductive barrier
  • rotational barrier
  • schottky barrier
  • several barrier
  • significant barrier
  • similar barrier
  • skin barrier
  • social barrier
  • societal barrier
  • species barrier
  • spinal cord barrier
  • strong barrier
  • structural barrier
  • substantial barrier
  • surface barrier
  • systemic barrier
  • technical barrier
  • testis barrier
  • thermal barrier
  • tissue barrier
  • trade barrier
  • tunnel barrier

  • Terms modified by Barriers

  • barrier breakdown
  • barrier coating
  • barrier damage
  • barrier diode
  • barrier disruption
  • barrier dysfunction
  • barrier effect
  • barrier film
  • barrier formation
  • barrier function
  • barrier height
  • barrier homeostasi
  • barrier impairment
  • barrier integrity
  • barrier island
  • barrier layer
  • barrier material
  • barrier membrane
  • barrier option
  • barrier permeability
  • barrier preventing
  • barrier property
  • barrier recovery
  • barrier reef
  • barrier reef marine park
  • barrier repair
  • barrier resistance
  • barrier status
  • barrier structure
  • barrier system
  • barrier thickness

  • Selected Abstracts


    JOURNAL OF PHYCOLOGY, Issue 4 2006
    Tom Schils
    The most eastern point of the Arabian Peninsula, Ras Al Hadd, marks the boundary between the Arabian Sea and the Gulf of Oman. This geographic landmark coincides with an abrupt floristic turnover, probably one of the sharpest biotic transitions known in marine biogeography. The floras of different Arabian localities across this floristic break were compared using macrophyte distribution data throughout the Indian Ocean and seasonal sea-surface temperature (SST) data. The localities from the Arabian Gulf and Gulf of Oman differ significantly from those of the Arabian Sea based on their species richness, species composition, average distribution range per species, general temperature affinity of the composing species, and seasonal temperature data of the coastal waters. Pooling the temperature data into two groups (SST3avg, average SST of the three warmest seasons; SSTmin, minimum of the seasonal SSTs) revealed a temperature limit at 28°C using both the temperature affinity data of the floras and the seasonal temperatures recorded for the specific Arabian localities, which significantly separates the Arabian Sea from localities of both Gulfs. Finally, SST data of the Indian Ocean were analyzed using this upper temperature threshold of macrophytes at 28°C and the lower temperature limit of corals at 25°C, revealing general macrophyte diversity patterns. [source]


    ARCHAEOMETRY, Issue 2 2005
    The Alpsas a barrier: ceramic remnants of the so-called Laugen-Melaun culture (c. 11th to c. sixth centuries bc) can be found in the northern Italy (Trentino/Alto Adige),eastern Switzerland,Liechtenstein and western Austria region. A petrographic study of 454 sherds from this area covering a time span of 500 years reveals the following. (1) The pottery from the Trentino/Alto Adige contains a predominantly volcanic temper, which can be linked to the volcanic rocks of the Bolzano area,in other words, to the core region of this culture. This material is therefore of a local/regional production. (2) These ceramics were imported from the Bolzano region to southeastern Switzerland (the Inn Valley) and the amount of imported pottery decreases markedly from the 11th century bc (approximately 70% imported) to the seventh to sixth centuries bc (approximately 10% imported). (3) No imported pottery can be detected north of the Alpine crest in Switzerland, Liechtenstein and Austria, and in this region serpentinite temper was preferred by ancient potters. These results demonstrate that long-lasting contacts and ceramic trade existed between the populations of the Inn Valley and the Trentino/Alto Adige. Such contacts could have been motivated by intermarriages between the two populations and/or economic exchange. The potters north of the Alpine ridge adopted the Laugen-Melaun style and produced such pottery locally. The use of serpentinite temper is puzzling and not related to any technological advantage. (Could it be recycled material? Or does it have any sociocultural specificity?) The Alps as a passage: 59 fragments of a black gloss ware, the so-called Campana, unearthed at 11 Late Latene sites (second to first centuries bc) in Switzerland and neighbouring Germany were analysed chemically by X-ray fluorescence. The results revealed: (1) that all of them were produced either in Italy or Lyon and then exported to the north; (2) that two principal south,north exchange routes existed, (a) fluviatile, along the Rhône,Rhine corridor and (b) trans-Alpine, using the Alpine passes, such as the Simplon and the Grand St Bernard. [source]


    ABSTRACT This paper examines pain and pain relief in the Caribbean, where pain is widely perceived as an unavoidable part of life, and where unnecessary suffering results from untreated and under treated pain. Barriers to pain relief in the Caribbean include patient and family attitudes, inadequate knowledge among health professionals and unduly restrictive regulations on the medical use of opioids. Similar barriers exist all over the world. This paper urges medical, nursing and public health professionals, and educators to examine attitudes towards pain and pain relief and to work towards making effective pain relief and palliation more accessible. It recommends that i) health professionals and officials be better educated about pain, palliation and opioids, ii) regulatory restrictions be updated in light of clinical and scientific evidence, iii) opioid procurement policies be adjusted to facilitate increased medical use, iv) medical charts and records be modified to routinely elicit and document patients levels of pain, and v) educational campaigns be developed to inform the public that moderate and severe pain can be safely relieved at the end of life and other stages of life. The professional, respectful, and beneficent response to patients in pain is to provide rapid and aggressive pain relief or to urgently consult a pain or palliative specialist. When a health system hinders such efforts the ethical response is to identify, facilitate and advocate for overcoming barriers to improvement. [source]


    ADDICTION, Issue 7 2010
    No abstract is available for this article. [source]


    EVOLUTION, Issue 8 2007
    S. Bergek
    Gene flow between coexisting or nearby populations normally prevents genetic divergence and local adaptation. Despite this, there are an increasing number of reports of sympatric sister taxa, indicating potential divergence and speciation in the face of gene flow. A large number of such reported cases involve lake-dwelling fish, which are expected to run into few physical barriers to dispersal within their aquatic habitat. However, such cases may not necessarily reflect sympatric speciation if cryptic dispersal barriers are common in lakes and other aquatic systems. In this study, we examined genetic differentiation in perch (Perca fluviatilis L.) from nine locations in a single, small lake (24 km2), using microsatellites. We detected significant genetic differentiation in all but two pairwise comparisons. These patterns were not consistent with divergence by distance or the existence of kin groups. Instead, they suggest that cryptic barriers to dispersal exist within the lake, allowing small-scale genetic divergence. Such an observation suggests that allopatric (or parapatric) divergence may be possible, even in small, apparently homogenous environments such as lakes. This has important consequences for how we currently view evidence from nature for sympatric speciation. [source]


    Kuo-I CHANG
    F13; F14; Q17 We investigate the impact of the elimination of import tariffs and nontariff policy barriers (NTPBs) on agricultural trade in a notional East Asian Free Trade Agreement using a Global Trade Analysis Project (GTAP)-based computable general equilibrium model. The investigation is divided into two parts. We first measure the NTPBs by employing a widely used method derived from the literature on border effects. Then, by adding into the GTAP database our estimates on the NTPBs, which the original GTAP database by its nature does incorporate, we compute the impact of the entire elimination of policy barriers (the complete reduction of import tariffs and NTPBs) on GDP. The result shows that there are remarkable differences between the effect of abolition of import tariffs and that of entire elimination of all import barriers. [source]


    BIOETHICS, Issue 8 2009
    ABSTRACT Clinical ethics committees have recently been established in nearly all Norwegian hospital trusts. One important task for these committees is clinical ethics consultations. This qualitative study explores significant barriers confronting the ethics committees in providing such consultation services. The interviews with the committees indicate that there is a substantial need for clinical ethics support services and, in general, the committee members expressed a great deal of enthusiasm for the committee work. They also reported, however, that tendencies to evade moral disagreement, conflict, and ,outsiders' are common in the hospitals. Sometimes even the committees comply with some of these tendencies. The committees agree that there is a need to improve their routines and procedures, clarify the committees' profile and field of responsibility, to make the committees well-known, to secure adequate operating conditions, and to develop organizational integration and support. Various strategies to meet these challenges on a local, regional or national level are also explored in this paper. [source]

    Recent Progress in Dielectric Barrier Discharges for Aerodynamic Flow Control

    G. I. Font
    Abstract Plasma actuators are electrical devices that use an atmospheric pressure dielectric barrier discharge for flow control. They have been employed successfully to promote boundary layer attachment. Simulations have been carried out of a plasma actuator using Direct-Simulation-Monte-Carlo and Particle-in-Cell methods. This work summarizes some recent results including: 1) the method by which force is imparted by the actuator to the neutral flow, 2) the effect of electronegative gasses, such as oxygen, and 3) the effects on the neutral flow of the plasma force. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    Rotational and Vibrational Temperature Measurements in a High-Pressure Cylindrical Dielectric Barrier Discharge (C-DBD)

    N. Masoud
    Abstract The rotational (TR) and vibrational (Tv) temperatures of N2 molecules were measured in a high-pressure cylindrical dielectric barrier discharge (C-DBD) source in Ne with trace amounts (0.02 %) of N2 and dry air excited by radio-frequency (rf) power. Both TR and Tv of the N2 molecules in the C 3,u state were determined from an emission spectroscopic analysis the 2nd positive system (C 3,u , B3,g). Gas temperatures were inferred from the measured rotational temperatures. As a function of pressure, the rotational temperature is essentially constant at about 360 K in the range from 200 Torr to 600 Torr (at 30W rf power) and increases slightly with increasing rf power at constant pressure. As one would expect, vibrational temperature measurements revealed significantly higher temperatures. The vibrational temperature decreases with pressure from 3030 K at 200 Torr to 2270 K at 600 Torr (at 30 W rf power). As a function of rf power, the vibrational temperature increases from 2520 K at 20 W to 2940 K at 60 W (at 400 Torr). Both TR and Tv also show a dependence on the excitation frequency at the two frequencies that we studied, 400 kHz and 13.56 MHz. Adding trace amounts of air instead of N2 to the Ne in the discharge resulted in higher TR and Tv values and in a different pressure dependence of the rotational and vibrational temperatures. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    The Blood,Brain Barrier and Epilepsy

    EPILEPSIA, Issue 11 2006
    Emily Oby
    Summary:, During the past several years, there has been increasing interest in the role of the blood,brain barrier (BBB) in epilepsy. Advances in neuroradiology have enhanced our ability to image and study the human cerebrovasculature, and further developments in the research of metabolic deficiencies linked to seizure disorders (e.g., GLUT1 deficiency), neuroinflammation, and multiple drug resistance to antiepileptic drugs (AEDs) have amplified the significance of the BBB's relationship to epilepsy. Prior to 1986, BBB research in epilepsy focused on three main areas: ultrastructural studies, brain glucose availability and transport, and clinical uses of AEDs. However, contrast-based imaging techniques and medical procedures such as BBB disruption provided a framework that demonstrated that the BBB could be reversibly disrupted by pathologic or iatrogenic manipulations, with important implications in terms of CNS drug delivery to "multiple drug resistant" brain. This concept of BBB breakdown for therapeutic purposes has also unveiled a previously unrecognized role for BBB failure as a possible etiologic mechanism in epileptogenesis. Finally, a growing body of evidence has shown that inflammatory mechanisms may participate in the pathological changes observed in epileptic brain, with increasing awareness that blood-borne cells or signals may participate in epileptogenesis by virtue of a leaky BBB. In this article we will review the relationships between BBB function and epilepsy. In particular, we will illustrate consensus and divergence between clinical reality and animal studies. [source]

    Electronic Control of the Rotational Barrier in ,2 -Alkyne-1-thio Complexes

    Wolfram W. Seidel
    Abstract A family of thio-alkyne complexes [Tp,Mo(CO)(L)(BnSC2S)] {Bn = benzyl, Tp, = hydrotris(3,5-dimethylpyrazolyl)borate, L = carbonyl (2), 2,6-dimethylphenyl isocyanide (7), tert -butyl isocyanide (8), 4-(dimethylamino)pyridine (9)} was prepared by reductive removal of a benzyl group in the corresponding bis(benzylthio)acetylene complexes [Tp,Mo(CO)(L)(BnSC2SBn)](PF6) (1 -PF6, 4 -PF6, 5 -PF6 and 6 -PF6). All complexes were characterized by IR, 1H, 13C spectroscopy and cyclic voltammetry. X-ray diffraction studies of 5 -PF6, 8 and 9 were carried out. The alkyne ligand is bound symmetrically to molybdenum in 5 -PF6 and unsymmetrically in 8 and 9. The trend in the ,-acidity of ligand L is reflected in the spectroscopic and electrochemical data as well as in the molecular structures. Variable temperature 1H NMR investigations with 7, 8 and 9 disclosed that the barrier of the alkyne rotation at molybdenum decreases in the order of rising electron density at the metal center while the steric demand increases. Therefore, electronic control of the barrier by the specific character of the ligand L is evident.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source]

    DFT/MM Study on Copper-Catalyzed Cyclopropanation , Enantioselectivity with No Enthalpy Barrier

    Galí Drudis-Solé
    Abstract The enantioselectivity in the reaction of [Cu(adam-box)(CHCO2Me)] {adam-box = 2,2,-isopropylidenebis[(4R)-(1-adamantyl)-2-oxazoline]} with Ph2C=CH2 was analyzed computationally by ONIOM(B3LYP:UFF) calculations. The lack of transition states in the potential-energy surface precludes the use of conventional approaches and requires the definition of reaction paths in an approximate Gibbs free-energy surface. The procedure is time consuming and intrinsically less accurate than the usual approaches based on enthalpic energy surfaces, but it produces results in reasonable agreement with experiment, which furthermore allow identification of the key interactions responsible for chiral discrimination.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source]

    Tunable Injection Barrier in Organic Resistive Switches Based on Phase-Separated Ferroelectric,Semiconductor Blends,

    Kamal Asadi
    Abstract Organic non-volatile resistive bistable diodes based on phase-separated blends of ferroelectric and semiconducting polymers are fabricated. The polarization field of the ferroelectric modulates the injection barrier at the semiconductor,electrode contact and, hence, the resistance of the comprising diodes. Comparison between the on- and off-current of the switching diodes, with the current measured for semiconductor-only diodes reveals that the switching occurs between bulk-limited, i.e., space-charge-limited, and injection-limited current transport. By deliberately varying the HOMO energy of the semiconductor and the work-function of the metal electrode, it is demonstrated that injection barriers up to 1.6,eV can be surmounted by the ferroelectric polarization yielding on/off current modulations of more than five orders of magnitude. The exponential dependence of the current modulation with a slope of 0.25,eV/decade is rationalized by the magnitude of the injection barrier. [source]

    Mineral Precipitation Upgradient from a Zero-Valent Iron Permeable Reactive Barrier

    R.L. Johnson
    Core samples taken from a zero-valent iron permeable reactive barrier (ZVI PRB) at Cornhusker Army Ammunition Plant, Nebraska, were analyzed for physical and chemical characteristics. Precipitates containing iron and sulfide were present at much higher concentrations in native aquifer materials just upgradient of the PRB than in the PRB itself. Sulfur mass balance on core solids coupled with trends in ground water sulfate concentrations indicates that the average ground water flow after 20 months of PRB operation was approximately twenty fold less than the regional ground water velocity. Transport and reaction modeling of the aquifer PRB interface suggests that, at the calculated velocity, both iron and hydrogen could diffuse upgradient against ground water flow and thereby contribute to precipitation in the native aquifer materials. The initial hydraulic conductivity (K) of the native materials is less than that of the PRB and, given the observed precipitation in the upgradient native materials, it is likely that K reduction occurred upgradient to rather than within the PRB. Although not directly implicated, guar gum used during installation of the PRB is believed to have played a role in the precipitation and flow reduction processes by enhancing microbial activity. [source]

    Keiretsu and Relationship-Specific Investment: A Barrier To Trade?

    Barbara J. Spencer
    This article develops a model of informal procurement within Japanese keiretsu so as to consider effects on intermediate-good imports, such as auto parts. Parts-suppliers make relationship-specific investments that benefit the automaker and prices are determined by bargaining after investment has been sunk. Although this investment raises efficiency, it limits the range of imports to less important parts, such as tailpipes, and it is possible that no parts are imported, despite lower foreign costs. Lack of information concerning investment rents combined with counterintuitive responses of imports to changes in output and costs could create unwarranted perceptions of a trade barrier. [source]

    Secularism as a Barrier to Integration?

    The French Dilemma
    ABSTRACT This article focuses on the secularism debate currently taking place in France by examining how this issue impacts the integration of immigrants, particularly Muslim immigrants. Secularism is one of the key values of French Republicanism, but one which has been challenged by the establishment of a settled population of Muslim immigrants in France. The issue has been particularly highlighted by the affaire des foulards (headscarf affair), an ongoing debate over the rights of Muslim girls to wear a headscarf to secular French schools. Discussions of the principle of secularism and of its application have been even more intense in recent months with the publication in December 2003 of a report by the Stasi Commission, a commission set up by President Chirac to investigate the application of the principle of secularism, and by the passage of legislation intended to outlaw the wearing of any "overt" religious insignia in French schools. This article examines these recent developments in the context of the long-running debate over Muslim women's right to wear a headscarf in French schools. It argues that the current focus on secularism provides evidence of the return of assimilation as a primary objective of public policy (Brubaker, 2001) and the decreasing strength of the movement in favour of the droit à la différence (right to difference). Finally, the paper argues that this has provided important obstacles to the integration of certain groups of immigrants, particularly Muslim immigrants. [source]

    The Complementary Membranes Forming the Blood-Brain Barrier

    IUBMB LIFE, Issue 3 2002
    Richard A. Hawkins
    Abstract Brain capillary endothelial cells form the blood-brain barrier. They are connected by extensive tight junctions, and are polarized into luminal (blood-facing) and abluminal (brain-facing) plasma membrane domains. The polar distribution of transport proteins allows for active regulation of brain extracellular fluid. Experiments on isolated membrane vesicles from capillary endothelial cells of bovine brain demonstrated the polar arrangement of amino acid and glucose transporters, and the utility of such arrangements have been proposed. For instance, passive carriers for glutamine and glutamate have been found only in the luminal membrane of blood-brain barrier cells, while Na-dependent secondary active transporters are at the abluminal membrane. This organization could promote the net removal of nitrogen-rich amino acids from brain, and account for the low level of glutamate penetration into the central nervous system. Furthermore, the presence of a ,-glutamyl cycle at the luminal membrane and Na-dependent amino acid transporters at the abluminal membrane may serve to modulate movement of amino acids from blood-to-brain. Passive carriers facilitate amino acid transport into brain. However, activation of the ,-glutamyl cycle by increased plasma amino acids is expected to generate oxoproline within the blood-brain barrier. Oxoproline stimulates secondary active amino acid transporters (Systems A and B o,+ ) at the abluminal membrane, thereby reducing net influx of amino acids to brain. Finally, passive glucose transporters are present in both the luminal and abluminal membranes of the blood-brain barrier. Interestingly, a high affinity Na-dependent glucose carrier has been described only in the abluminal membrane. This raises the question whether glucose entry may be regulated to some extent. Immunoblotting studies suggest more than one type of passive glucose transporter exist in the blood-brain barrier, each with an asymmetrical distribution. In conclusion, it is now clear that the blood-brain barrier participates in the active regulation of brain extracellular fluid, and that the diverse functions of each plasma membrane domain contributes to these regulatory functions. [source]

    Are Patient Preferences for Life-Sustaining Treatment Really a Barrier to Hospice Enrollment for Older Adults with Serious Illness?

    David Casarett MD
    OBJECTIVES: To determine whether patient preferences are a barrier to hospice enrollment. DESIGN: Prospective cohort study. SETTING: Fifteen ambulatory primary care and specialty clinics and three general medicine inpatient units. PARTICIPANTS: Two hundred three seriously ill patients with cancer (n=65, 32%), congestive heart failure (n=77, 38%), and chronic obstructive pulmonary disease (n=61, 30%) completed multiple interviews over a period of up to 24 months. MEASUREMENTS: Preferences for high- and low-burden life-sustaining treatment and site of death and concern about being kept alive by machines. RESULTS: Patients were more likely to enroll in hospice after interviews at which they said that they did not want low-burden treatment (3 patients enrolled/16 interviews at which patients did not want low-burden treatment vs 47 patients enrolled/841 interviews at which patients wanted low-burden treatment; relative risk (RR)=3.36, 95% confidence interval (CI)=1.17,9.66), as were interviews at which patients said they would not want high-burden treatment (5/28 vs 45/826; RR=3.28, 95% CI=1.14,7.62), although most patients whose preferences were consistent with hospice did not enroll before the next interview. In multivariable Cox regression models, patients with noncancer diagnoses who desired low-burden treatment (hazard ratio (HR)=0.46, 95% CI=0.33,0.68) were less likely to enroll in hospice, and those who were concerned that they would be kept alive by machines were more likely to enroll (HR=5.46, 95% CI=1.86,15.88), although in patients with cancer, neither preferences nor concerns about receiving excessive treatment were associated with hospice enrollment. Preference for site of death was not associated with hospice enrollment. CONCLUSION: Overall, few patients had treatment preferences that would make them eligible for hospice, although even in patients whose preferences were consistent with hospice, few enrolled. Efforts to improve end-of-life care should offer alternatives to hospice that do not require patients to give up life-sustaining treatment, as well as interventions to improve communication about patients' preferences. [source]

    Plasticizer Effect on Grease Barrier and Color Properties of Whey-protein Coatings on Paperboard

    S.-Y. Lin
    ABSTRACT Whey protein concentrates with ,80% protein (WPC-80) plasticized with 0.64 M glycerol or sucrose, or with 0.34 or 0.64 M sorbitol or polyethylene glycol (PEG) 200, produced flexible films. WPC-80 with hydrolyzed lactose required addition of less sucrose to produce flexible films. WPC-80 films formed as coatings on paperboard gave a grease barrier comparable to WPI film-coatings. Long-term ambient storage of WPC-80 coated paperboard indicated that the use of sucrose as plasticizer imparted good grease resistance and minimized plasticizer migration. [source]

    Poster Sessions CP10: Blood,Brain Barrier

    M. A. García
    Kinetic analysis of vitamin C uptake has demonstrated that specialized cells take up ascorbic acid (AA), the reduced form of vitamin C, through sodium-AA cotransporters. Recently, two different isoforms of sodium-vitamin C cotransporters (SVCT 1, 2) that mediate high affinity Na+ -dependent l -ascorbic acid have been cloned. SVCT2 was detected mainly in choroid plexus cells and neurons, however, there are no evidences of SVCT2 expression in glial cells. High concentrations of vitamin C has been demonstrated in brain hypothalamic area. The hypothalamic glial cells, known as alpha and beta tanycytes, are specialized ependymal cells that bridge the cerebrospinal fluid and the portal blood of the median eminence. Our hypothesis postulates that tanycytes take up reduced vitamin C from the portal blood and cerebrospinal fluid generating an high concentration of this vitamin in brain hypothalamic area. In situ immunohistochemical analyses demonstrated that SVCT2 transporter is selectively expressed in apical region of tanycytes. A newly developed primary culture of mouse hypothalamic tanycytes was used to confirm the expression and function of SVCT2 isoform in these cells. Reduced vitamin C uptake was temperature and sodium dependent. Kinetic analysis showed an apparent Km of 20 ,m and a Vmax of 45 pmol/min per million cells for the transport of ascorbic acid. The expression of SVCT2 was confirmed by immunoblots and RT,PCR. Tanycytes may perform a neuroprotective role concentrating the vitamin C in the hypothalamic area. Acknowledgements:, Supported by Grands FONDECYT 1010843 and DIUC-GIA 201.034.006-1.4 from Concepción University. [source]

    A General Approach to Hedging Options: Applications to Barrier and Partial Barrier Options

    Hans-Peter Bermin
    In this paper we consider a Black and Scholes economy and show how the Malliavin calculus approach can be extended to cover hedging of any square integrable contingent claim. As an application we derive the replicating portfolios of some barrier and partial barrier options. [source]

    Barrier to gene flow between two ecologically divergent Populus species, P. alba (white poplar) and P. tremula (European aspen): the role of ecology and life history in gene introgression

    MOLECULAR ECOLOGY, Issue 4 2005
    C. LEXER
    Abstract The renewed interest in the use of hybrid zones for studying speciation calls for the identification and study of hybrid zones across a wide range of organisms, especially in long-lived taxa for which it is often difficult to generate interpopulation variation through controlled crosses. Here, we report on the extent and direction of introgression between two members of the ,model tree' genus Populus: Populus alba (white poplar) and Populus tremula (European aspen), across a large zone of sympatry located in the Danube valley. We genotyped 93 hybrid morphotypes and samples from four parental reference populations from within and outside the zone of sympatry for a genome-wide set of 20 nuclear microsatellites and eight plastid DNA restriction site polymorphisms. Our results indicate that introgression occurs preferentially from P. tremula to P. alba via P. tremula pollen. This unidirectional pattern is facilitated by high levels of pollen vs. seed dispersal in P. tremula (pollen/seed flow = 23.9) and by great ecological opportunity in the lowland floodplain forest in proximity to P. alba seed parents, which maintains gene flow in the direction of P. alba despite smaller effective population sizes (Ne) in this species (P. alba Nec. 500,550; P. tremula Nec. 550,700). Our results indicate that hybrid zones will be valuable tools for studying the genetic architecture of the barrier to gene flow between these two ecologically divergent Populus species. [source]

    Water Barrier Ship Self Defense Lethality

    Charles E. Higdon
    ABSTRACT The Naval Surface Warfare Center Dahlgren Division has investigated technology for the Office of Naval Research (ONR) that has the potential to be very effective in defending Navy platforms against high-speed, sea-skimming anti-ship cruise missiles (ASCMs). This technology uses a new kill mechanism, a wall of water, to provide a low cost, universal terminal defense system for Navy ships. The Water Barrier or wall of water is generated from the shallow detonation of multiple underwater explosive charges to protect the ship from attacking sea skimmers. This terminal defense concept can be employed to slow or stop debris and warhead fragments from missiles killed at short range to preclude significant damage to own ship. Furthermore, the Water Barrier would defeat the fuzing and structure of ASCMs that have penetrated the inner self-defense layer. This paper describes the Water Barrier Concept that provides terminal defense for Navy ships, the formation of the wall of water that defeats sea skimming ASCMs, and the field tests that demonstrate the viability of the concept. Finally, this paper documents the 1997 field test results that demonstrate the lethality of the Water Barrier against tactical battlefield missile warheads and structures. [source]

    The Credit Hour as a Potential Barrier to Innovation: Lessons from Innovative Institutions

    Thomas Ehrlich
    The premise of the credit hour is the equation of student learning with class time. Leaders at institutions particularly known for innovations in student learning have found ways to work with and around the metric, although it remains an obstacle to innovation at most institutions. [source]

    Skin Barrier, Hydration, and pH of the Skin of Infants Under 2 Years of Age

    Francesca Giusti M.D.
    A total of 70 infants, 45 girls and 25 boys, ages 8,24 months, and 30 healthy women were studied by means of transepidermal water loss (TEWL), capacitance, and pH measurements at two different skin sites, the volar forearm and the buttocks. No significant differences in TEWL were found between infants and adults, either on the buttocks or on the volar forearm. On the contrary, capacitance values were higher in infants. Their skin also appeared less acid than that of adults, with high statistical significance. No TEWL, capacitance, or pH variations were observed in infants according to sex and age. On the basis of the above data, the skin of infants 8,24 months of age shows functional signs of immaturity. This may lead to an increased permeability and a reduced capacity for defense against chemical and microbial aggression. [source]

    Silver-Loaded Cotton/Polyester Fabric Modified by Dielectric Barrier Discharge Treatment

    Mirjana Kosti
    Abstract The preparation of antimicrobial silver-loaded cotton/polyester fabrics has been carried out by DBD surface activation followed by silver sorption from aqueous silver nitrate solution. A series of DBD fabric treatments was performed in order to determine the most suitable experimental conditions for the fabric surface activation. The capillarity, silver ion uptake, and copper number were used to assess the surface changes on the fabrics. An effective process has been developed to obtain antimicrobial silver-loaded Co/PES fabrics. The antimicrobial activity of the silver-loaded fabrics against different pathogens was evaluated in vitro. The quantity of bonded silver ions is enough to develop desirable antimicrobial activity in the Co/PES fabrics. [source]

    Atmospheric Cold Plasmas for Synthesizing Nanocrystalline Anatase TiO2 using Dielectric Barrier Discharges

    Long-Hui Nie
    Abstract Nanocrystalline anatase TiO2 has been successfully synthesized using TiCl4 and O2 as precursors by atmospheric cold plasmas generated by dielectric barrier discharges (DBD) without extra heating or thermal treatment. For the TiO2 powders synthesized by DBD plasma at an energy density of 5.9 kJ,·,L,1, XRD and TEM analyses revealed that the nanocrystallite size is about 10,15 nm. Only a single crystalline structure of anatase was observed performing XRD, HRTEM and SAED measurements. It was found that the particle size decreased with increasing the discharge power, and that the chlorine contamination dramatically decreased when using high discharge power levels. [source]

    Atmospheric Pressure Barrier Discharge Deposition of Silica-Like Films on Polymeric Substrates

    Sergei Starostine
    Abstract Silica-like coatings were deposited on polymer foils in APG discharge in a roll-to-roll configuration. The dependence of film structure and chemical composition on the conditions during deposition process was studied by means of SEM, ATR-FTIR, and XPS analysis. The influence of oxidant concentration on the deposited film properties is analyzed and discussed. It was observed that pulsing of the APG discharge suppresses dust formation in atmospheric plasma and, therefore, provides uniform coatings. [source]

    Transient Barrier Discharge Characteristics of Parallel-Plate-Type, Packed-Bed, Non-Thermal Plasma Reactor Under High-Humidity Conditions

    Jen-Shih Chang
    Abstract Summary: Barrier discharge has been used for ozone generation for water treatments and pollutant gas removal. An experiment has been conducted to observe transient barrier discharge characteristics of parallel-plate-type, 3 mm diameter, spherical glass beads packed-bed, non-thermal plasma reactors under high-humidity conditions. The results show that: 1) steady operation of the reactor requires 5 to 10 min of operation under an initial 20 to 80% relative humidity at 20,°C in air, as a result of the desorption of water from the packed materials, 2) the usual method to determine discharge power using a Q - V Lissajous figure may be distorted by adsorption/desorption of water vapor from the surface, and 3) since the surface of the packed material is heated to 50 to 160,°C, the mechanism of desorption may be a result of pure thermal effects. Change in reactor surface temperature with time. [source]

    Barrier and mechanical properties of injection molded montmorillonite/polyesteramide nanocomposites

    M. Krook
    Properties of injection-molded biodegradable polyesteramide composites containing 5 and 13 wt% octadecylammonium-treated montmorillonite clay have been studied. Oxygen transmission rates and mechanical properties were measured. X-ray diffraction was used to assess the degree of intercalation of the clay layer stacks, and transmission electron microscopy (TEM) was used to assess the morphology and degree of layer delamination. A substantial reduction in oxygen permeability was observed when clay was added to the composites. The oxygen permeability of the 13 wt% clay sample was only 20% of that of the pure polymer. The in-plane stiffness and in-plane strength of the sheets were greatly improved without any embrittlement. These beneficial effects were probably due to the high degree of clay layer exfoliation and orientation observed by TEM. Heat shrinkage, toughness analysis, and cutting operations suggested that the polymer chains and the clay layers were oriented parallel to the plane of the sheet. TEM and X-ray showed that stacked layers were still present but that these were significantly intercalated. The clay-layer periodic spacing increased from 25 Å to approximately 35 Å during processing. POLYM. ENG. SCI. 45:135,141, 2005. © 2004 Society of Plastics Engineers [source]