bluuebunny/crossref_metadata_2025 huggingface dataset:
Exploring the chemical enhancement for surface-enhanced Raman scattering with Au bowtie nanoantennas
Authors: Fromm David P. , Sundaramurthy Arvind , Kinkhabwala Anika , Schuck P. James , Kino Gordon S. , Moerner W. E.
Published: February 2006

Single metallic bowtie nanoantennas provide a controllable environment for surface-enhanced Raman scattering (SERS) of adsorbed molecules. Bowties have experimentally measured electromagnetic enhancements, enabling estimation of chemical enhancement for both the bulk and the few-molecule regime. Strong fluctuations of selected Raman lines imply that a small number of p-mercaptoaniline molecules on a single bowtie show chemical enhancement >107, much larger than previously believed, likely due to charge transfer between the Au surface and the molecule. This chemical sensitivity of SERS has significant implications for ultra-sensitive detection of single molecules.
Anomalous temperature dependence of electrical conductance of DNA-linked Au nanoparticle aggregates
Authors: Yun Yong Ju , Park Gwangseo , Jung Sunkyung , Ha Dong Han
Published: February 2006

We have measured the electrical conductance of DNA-linked Au nanoparticle aggregates using the four probe method. FE-SEM images show that the Au nanoparticles are remained intact but not fused together. As the temperature increases under a constant relative humidity, the electrical conductance of Au nanoparticle aggregates linked by 12 base DNA molecules increases exponentially with an anomaly around the melting temperature of the linker DNAs due to the abrupt change of the amount of water molecules adsorbed on DNAs, but we could not observe such an anomaly for the aggregates linked by 24 base DNAs up to 71°C. We expect our results can be utilized as a DNA detection method which does not require any thermal-stringency wash before the measurement at each temperature.
Observation of optical instabilities in the photoluminescence of InGaN single quantum well
Authors: Micheletto Ruggero , Abiko Masayoshi , Kaneta Akio , Kawakami Yoichi , Narukawa Yukio , Mukai Takashi
Published: February 2006

We investigate a peculiar optical instability (blinking) phenomena associated with spatial inhomogeneity in InxGa(1−x)N single quantum well systems. We studied the time dependence of this dynamic phenomenon and tested a “quantum jump” single exponential model on the system. A comparative analysis of the behavior of different samples suggests that indium-rich localized centers participate in the mechanism of blinking and that the instability behavior differs with the excitation wavelength. Our study indicates that the trapping and de-trapping process between the localized-luminescent centers and surrounding less luminous regions plays important roles in the carrier recombination mechanism.
Switching spectroscopy piezoresponse force microscopy of ferroelectric materials
Authors: Jesse Stephen , Baddorf Arthur P. , Kalinin Sergei V.
Published: February 2006

The application of ferroelectric materials for electronic devices necessitates the quantitative study of local switching behavior, including imprint, coercive bias, remanent and saturation responses, and work of switching. Here we introduce switching spectroscopy piezoresponse force microscopy as a tool for real-space imaging of switching properties on the nanoscale. The hysteresis curves, acquired at each point in the image, are analyzed in the thermodynamic and kinetic limits. We expect that this approach will further understanding of the relationships between material microstructure and polarization switching phenomena on the nanoscale, and provide a quantitative tool for ferroelectric-based device characterization.
Electrical spin injection from ZnMnSe into InGaAs quantum wells and quantum dots
Authors: Löffler W. , Tröndle D. , Fallert J. , Kalt H. , Litvinov D. , Gerthsen D. , Lupaca-Schomber J. , Passow T. , Daniel B. , Kvietkova J. , Grün M. , Klingshirn C. , Hetterich M.
Published: February 2006

We report on efficient injection of electron spins into InGaAs-based nanostructures. The spin light-emitting diodes incorporate an InGaAs quantum well or quantum dots, respectively, as well as a semimagnetic ZnMnSe spin-aligner layer. We show a circular polarization degree of up to 35% for the electroluminescence from InGaAs quantum wells and up to 21% for InGaAs quantum dots. We can clearly attribute the polarization of the emitted photons to the spin alignment in the semimagnetic layer by comparison to results from reference devices (where the ZnMnSe is replaced by ZnSe) and from all-optical measurements.
Monte Carlo simulation of hot phonon effects in resonant-phonon-assisted terahertz quantum-cascade lasers
Authors: Lü J. T. , Cao J. C.
Published: February 2006

We study the influence of nonequilibrium optical phonons on the electron transport in resonant-phonon-assisted terahertz (THz) quantum-cascade lasers (QCLs). The hot phonon effect is included in the Monte Carlo simulation by introducing a time constant accounting for the decay of polar optical phonons into other phonon modes. We find that nonequilibrium polar optical phonons may modify the electron-phonon interaction, affect the electron distribution in different subbands, and consequently change the device current. We conclude that the hot phonon effect should be taken into account in the study of the transport properties of resonant-phonon-assisted THz QCLs.
Use of a long-duration ns pulse for efficient emission of spectral lines from the laser ablation plume in water
Authors: Sakka Tetsuo , Oguchi Hisayuki , Masai Satoru , Hirata Kohichi , Ogata Yukio H. , Saeki Morihisa , Ohba Hironori
Published: February 2006

The effect of pulse duration upon the line profile of Cu I emission observed by laser ablation of a copper metal plate immersed in water has been examined. By irradiating a pulse with the duration longer than 40 ns the spectral profile with clear narrow emission lines of Cu atoms is obtained, while the emission spectra always suffer from broadening and self-absorption by the irradiation of the 20 ns pulse for the ablation. The results show that the use of a long-duration pulse enables in situ elemental analysis of the solid surface in contact with a bulk liquid.
Effects of hydrogen on majority carrier transport and minority carrier lifetimes in long wavelength infrared HgCdTe on Si
Authors: Boieriu P. , Grein C. H. , Velicu S. , Garland J. , Fulk C. , Sivananthan S. , Stoltz A. , Bubulac L. , Dinan J. H.
Published: February 2006

We present the results of using an electron cyclotron resonance (ECR) plasma to incorporate hydrogen into long wavelength infrared HgCdTe layers grown by molecular beam epitaxy. Both as-grown and annealed layers doped in situ with indium were hydrogenated. Secondary ion mass spectroscopy confirmed the incorporation of hydrogen. Hall and photoconductive lifetime measurements were used to assess the effects of the hydrogenation. Increases in the electron mobilities and minority carrier lifetimes were observed for almost all ECR conditions.
Titanium plasma source for capillary discharge extreme ultraviolet lasers
Authors: Shuker M. , Ben-kish A. , Fisher A. , Ron A.
Published: February 2006

A technique to generate jets of pure Titanium plasma is presented. A Ti wire is exploded in an Alumina capillary sealed with 1 atm. of air inside. The generated plasma emerges from the capillary (to a high-vacuum environment) by ripping a thin Ti foil that seals one of the capillary ends. The generated plasma jets have a velocity of up to 4.5±0.5mm∕μs, an electron temperature of 1.5±0.5eV and an ion density of 2.7±1×1017∕cc. The plasma source was designed for a capillary discharge extreme ultraviolet laser experiment, but might also be useful to other application such as a target for Z-pinch experiments.
Demonstration of quasi-phase-matched nonreciprocal polarization rotation in III-V semiconductor waveguides incorporating magneto-optic upper claddings
Authors: Holmes B. M. , Hutchings D. C.
Published: February 2006

The demonstration of quasi-phase-matched nonreciprocal polarization rotation in a waveguide comprising a conventional III-V semiconductor core and lower cladding is reported. The approach, which is achieved through the incorporation of a periodic upper cladding that alternates between magneto-optic and nonmagneto-optic media, overcomes many of the problems traditionally encountered when transferring the principles of free-space Faraday-effect optical isolators into waveguide geometries. An enhancement of polarization rotation many times greater than that achievable in the absence of phase matching is observed. Additionally, the technique facilitates an ability to select and/or manipulate individual modes from multimode waveguides.
Detection of pico-Tesla magnetic fields using magneto-electric sensors at room temperature
Authors: Zhai Junyi , Xing Zengping , Dong Shuxiang , Li Jiefang , Viehland D.
Published: February 2006

The measurement of low-frequency (10−2–103Hz) minute magnetic field variations (10−12Tesla) at room temperature in a passive mode of operation would be critically enabling for deployable neurological signal interfacing and magnetic anomaly detection applications. However, there is presently no magnetic field sensor capable of meeting all of these requirements. Here, we present new bimorph and push-pull magneto-electric laminate composites, which incorporate a charge compensation mechanism (or bridge) that dramatically enhances noise rejection, enabling achievement of such requirements.
Employing ambipolar oligofluorene as the charge-generation layer in time-of-flight mobility measurements of organic thin films
Authors: Hung Wen-Yi , Ke Tung-Huei , Lin Yu-Ting , Wu Chung-Chih , Hung Tsung-Hsi , Chao Teng-Chih , Wong Ken-Tsung , Wu Chih-I
Published: February 2006

Strong absorption of oligofluorenes at wavelengths of a few commonly used nanosecond pulsed lasers, their bipolar transport characteristics, and high mobilities for both holes and electrons make them useful as the general and effective charge-generation material for the time-of-flight mobility measurement of organic materials. In this letter, we demonstrate the use of the terfluorene as the charge-generation material for measuring hole and electron mobilities of various organic materials. Such a scheme has the advantages of simplifying the instrumentation and reducing material consumption in the measurements.
Optical properties of nanocrystalline FeSi2 and the effects of hydrogenation
Authors: Takarabe K. , Doi H. , Mori Y. , Fukui K. , Shim Y. , Yamamoto N. , Yoshitake T. , Nagayama K.
Published: February 2006

Various optical measurements confirm that optical absorption in uniform thin films made from nanocrystalline iron disilicide (nc-FeSi2) with a 3–5nm radius is larger by about 10% than that of single crystalline β-FeSi2. It is also found that the hydrogenation of nc-FeSi2 changes strongly its optical characteristic energies. The nanocrystalline state appears characteristically in the imaginary part of dielectric constants of β-FeSi2 around 2–3eV.
In situ observations of crack propagation mechanisms along interfaces between confined polymer layers and glass
Authors: Vellinga W. P. , Timmerman R. , van Tijum R. , De Hosson J. Th. M.
Published: February 2006

This paper concentrates on microscopic observations of the propagation of cracks along polymer-glass interfaces and crack propagation mechanisms. The experimental set-up consists of an asymmetric double cantilever beam in an optical microscope. Image processing techniques used to isolate the crack fronts are presented. The fronts propagate inhomogeneously in space and time, i.e., in bursts that spread laterally along the front over a certain distance. It is interesting to note that two different cases are detected; one in which crack propagation is dominated by initiation of instabilities on the front, and another one in which it is dominated by propagation of existing instabilities.
Melting and optical properties of ZnO nanorods
Authors: Su Xin , Zhang Zhengjun , Zhu Minmin
Published: February 2006

We observed that, by heating in air, the ZnO nanorods could start to melt at a temperature of ∼750°C, which is greatly reduced comparing with that of the bulk form. Prolonged annealing at this temperature resulted in partial melting of individual nanorods and the coalescence of the nanorods with their neighbors, leading to a great change in their optical properties, i.e., a new photoluminescence peak emerged at ∼468nm. Further analysis indicated that the new photoluminescence is closely related to the melting and the coalescence of the ZnO nanorods which probably induced some defects by thermal annealing at this temperature.
Fe
∕
Mg
O
interface engineering for high-output-voltage device applications
Authors: Tiusan C. , Sicot M. , Hehn M. , Belouard C. , Andrieu S. , Montaigne F. , Schuhl A.
Published: February 2006

The magnetotransport characteristics of Fe∕MgO∕Fe epitaxial tunnel junctions are reported. For clean Fe∕MgO interfaces, a tunnel magnetoresistance of 150% is measured. However, the magnetoresistance decreases rapidly with the applied voltage. Consequently, the main parameter to optimize for device application, namely the output voltage, remains relatively low. This limitation has been solved by interface engineering through the insertion of carbon impurities at the Fe∕MgO interface. Although the tunnel magnetoresistance amplitude is slightly reduced, its variation versus the applied voltage becomes strongly asymmetric with large magnetoresistance maintained up to 1.5V. This determines a large increase of the tunnel junction output voltage.
Lattice vibrations in hexagonal Ga1−xMnxN epitaxial films on c-plane sapphire substrates by infrared reflectance spectra
Authors: Hu Z. G. , Strassburg M. , Weerasekara A. , Dietz N. , Perera A. G. U. , Kane M. H. , Asghar A. , Ferguson I. T.
Published: February 2006

The lattice vibrations of undoped hexagonal Ga1−xMnxN (x from 0.0% to 1.5%) epitaxial films grown on c-plane sapphire substrates by metalorganic chemical vapor deposition have been investigated using infrared reflectance spectra in the frequency region of 200–2000cm−1 (5–50μm) at room temperature. The experimental reflectance spectra were analyzed using the Lorentz oscillator model for infrared-active phonon observed. The E1(LO) phonon frequency slightly decreases with increasing Mn composition. However, the E1(TO) phonon frequency linearly increases with the Mn composition, which can be well expressed by (558.7+350x)cm−1 and the broadening values are found to be larger than that of the GaN film. It indicates that Mn incorporation decreases the peak values (from the E1 phonon) of the infrared dielectric functions due to the local variation in the lattice constants and to the destruction of the crystal translational symmetry.
Dielectric properties of ⟨001⟩-oriented Ba0.6Sr0.4TiO3 thin films on polycrystalline metal tapes using biaxially oriented MgO∕γ-Al2O3 buffer layers
Authors: Choi W. , Kang B. S. , Jia Q. X. , Matias V. , Findikoglu A. T.
Published: February 2006

We report the growth of ⟨001⟩-oriented Ba0.6Sr0.4TiO3 (BST) thin films on polycrystalline Ni-alloy tapes by pulsed laser deposition using biaxially oriented, ion-beam-assisted deposited (IBAD) MgO and γ-Al2O3 buffer layers. Dielectric constant values of our BST films were up to ∼85% of those in the epitaxial films prepared under similar conditions on single-crystal MgO substrates. No significant dispersion of the dielectric constant was observed for frequencies from 100Hz to 1MHz. These results demonstrate the versatility of using IBAD-textured MgO and γ-Al2O3 buffer layers to integrate highly oriented good-quality BST films with nonsingle-crystalline substrates.
Towards the development of a Cavendish banana resistant to race 4 of fusarium wilt: gamma irradiation of micropropagated Dwarf Parfitt (Musa spp., AAA group, Cavendish subgroup)
Authors: Smith M. K. , Hamill S. D. , Langdon P. W. , Giles J. E. , Doogan V. J. , Pegg K. G.
Published: February 2006

‘Dwarf Parfitt’, an extra-dwarf Cavendish cultivar with resistance to subtropical race 4 Fusarium oxysporum f. sp. cubense (Foc), was gamma irradiated at a dose of 20 Gy and putative mutants were recovered with improved agronomic characteristics. Further screening of putative mutants for improved yield and fruit size, as well as a degree of resistance to fusarium wilt, led to the selection of a line (DPM25) with improved productivity when grown on soils infested with subtropical race 4 Foc. DPM25 was equal to the industry standard, ‘Williams’, in every agronomic trait measured and it consistently showed a lower incidence of fusarium wilt. Further improvement of field resistance to race 4 Foc is needed in DPM25 and further cycles of mutation induction and selection is an option discussed.
Effect of seed coating on the accuracy of single-seed sowing of sesame under field conditions
Authors: Barut Z. B. , Çağırgan M. I.
Published: February 2006

Sesame seed treatments consisted of 2 different coatings and uncoated seeds. These were tested to determine their effect on accuracy of plant spacing after emergence in single-seed sowing under different field conditions. Seedbed treatments were composed of traditional tillage without crop residue and conservative tillage with wheat stubble. To quantify plant spacing accuracy and emergence uniformity, spacing between plants within a row and plant emergence per day were measured. The measurements were used to calculate the quality of feed index, multiples index, skip index, precision, emergence rate index, mean emergence date and the percentage of emergence. It was concluded that seed treatments had a significant effect on multiples index and skip index of horizontal distribution pattern and emergence rate index, mean emergence date and the emergence percentage. The coating acted negatively on seed germination and led to missing plants and less plant spacing uniformity in the row. The shortest emergence date and maximum percentage of emergence and quality of feed index were obtained with uncoated sesame seeds. The parameters, except emergence rate index, were not affected statistically by tillage treatments. It was found that all seeds emerged in less time on conservation tillage plots with stubble.
Quality of fresh and dried fruit of apricot (cv. Moorpark) in response to soil-applied nitrogen
Authors: Rettke M. A. , Pitt T. R. , Maier N. A. , Jones J. A.
Published: February 2006

The effects of soil applications of nitrogen on the quality of fresh and dried fruit from 12-year-old apricot Prunus armeniaca cultivar Moorpark trees growing on an orthic Tenosol in the Riverland region of South Australia were studied over 3 years. The experiment was set up in a randomised complete block design with 6 annual rates of nitrogen (0, 250, 500, 750, 1000 and 1250 g/tree.year) applied in the form of ammonium nitrate. Application was split into 30% at budburst, 30% six weeks after budburst and 40% after harvest. Firmness of fruit was significantly reduced as the rate of applied nitrogen increased. The flesh of individual fruits ripened more evenly when 0 or 250 g nitrogen/tree.year was applied, compared with rates in the range 500–1250 g nitrogen/tree.year. Application of nitrogen significantly increased the pH of fruit. The total soluble solids level of fruit from trees that received 0 or 250 g nitrogen/tree.year, was significantly lower than from trees that received 750 or 1250, but not 1000 g nitrogen/tree.year. Application of nitrogen did not significantly affect the concentration of sulfur dioxide in fresh fruit measured after sulfuring, but the concentration of sulfur dioxide in fruit at the completion of drying was significantly increased. The application of nitrogen did not affect the drying ratio of fruit. Nitrogen application increased the rate of darkening of dried apricots in storage in each of the three years. Relationships were found between time taken for dried apricots to darken to an unacceptable level and nitrogen concentration in harvested fruit. It is suggested that to assist in the management of darkening of dried apricots in storage, annual nitrogen application rates on an orthic Tenosol need to be below 500 g/tree.year and ideally below 250 g/tree.year.
Quorum sensing and multidrug transporters in
Escherichia
coli
Authors: Yang Shirley , Lopez Christopher R. , Zechiedrich E. Lynn
Published: February 2006

Previously, we found that the quorum sensing transcription factor SdiA up-regulates AcrAB. Others found that a 4-quinolone was a quorum-sensing signal in
Pseudomonas aeruginosa
. In
Escherichia coli
, there are at least three multidrug transporters (AcrAB∕TolC, MdfA, and NorE) that exude fluoroquinolones. Here, we show that Δ
acrAB
,
tolC210
, or Δ
norE
mutants have the same growth rate as WT cells in exponential phase but grow to higher cell density in stationary phase. Overproduction of either pump caused cells to reach lower density.
mdfA
had no effect. Conditioned medium (CM) from cells overexpressing
acrAB
represses cell growth more than CM from WT cells. CM from pump mutant cells represses cell growth less than CM from WT cells. These results were not affected by the deletion of luxS, which synthesizes the quorum-sensing signal autoinducer 2 (AI-2). Expression of the
rpoS
gene encoding the stationary phase σ factor is induced earlier in cells overexpressing
acrAB
and later in
acrAB
mutant cells. These results support a model in which a natural function of AcrAB∕TolC and NorE is to export signals for cell–cell communication. Drugs exported by pumps may resemble communication molecules normally exuded.
ALADIN
I482S
causes selective failure of nuclear protein import and hypersensitivity to oxidative stress in triple A syndrome
Authors: Hirano Makito , Furiya Yoshiko , Asai Hirohide , Yasui Akira , Ueno Satoshi
Published: February 2006

Triple A syndrome is an autosomal recessive neuroendocrinological disease caused by mutations in a gene that encodes 546 amino acid residues. The encoded protein is the nucleoporin ALADIN, a component of nuclear pore complex (NPC). We identified a mutant ALADIN
I482S
that fails to target NPC and investigated the consequences of mistargeting using cultured fibroblasts (I482Sf) from a patient with triple A syndrome. ALADIN
I482S
affected a
karyopherin
-α/β-mediated import pathway and decreased nuclear accumulations of aprataxin (APTX), a repair protein for DNA single-strand breaks (SSBs), and of DNA ligase I in I482Sf. This decrease was restored by wild-type ALADIN. ALADIN
I482S
had no effect on imports of M9/
kap
-β2, BIB/
kap
-β3, histone H1/importin 7, the ubiquitin conjugating enzyme UbcM2/importin 11, or the spliceosome protein U1A, indicating that ALADIN
I482S
selectively impaired transport of discrete import complexes through NPC. Cell survival assay showed hypersensitivity of I482Sf to
l
-buthionine-(S,R)-sulfoximine (BSO), a glutathione-depleting agent. BSO decreased nuclear APTX and ligase I levels in I482Sf and normal control fibroblasts, but increased SSBs only in I482Sf. These observations implied that I482Sf are hypersensitive to BSO and no longer sufficiently repair SSBs. Consistent with this notion, I482Sf transfected with both APTX and ligase I had increased resistance to BSO, whereas I482Sf transfected with LacZ vector remained hypersensitive to BSO. We propose that oxidative stress aggravates nuclear import failure, which is already compromised in patient cells. Consequent DNA damage, beyond the limited capacity of DNA repair proteins, i.e., APTX and ligase I, may participate in triggering cell death.
Streptococcal modulation of cellular invasion via TGF-β1 signaling
Authors: Wang Beinan , Li Shaoying , Southern Peter J. , Cleary Patrick P.
Published: February 2006

Group AStreptococcus(GAS) and other bacterial pathogens are known to interact with integrins as an initial step in a complex pathway of bacterial ingestion by host cells. Efficient GAS invasion depends on the interaction of bound fibronectin (Fn) with integrins and activation of integrin signaling. TGF-β1 regulates expression of integrins, Fn, and other extracellular matrix proteins, and positively controls the integrin signaling pathway. Therefore, we postulated that TGF-β1 levels could influence streptococcal invasion of mammalian cells. Pretreatment of HEp-2 cells with TGF-β1 increased their capacity to ingest GAS when the bacteria expressed fibronectin-binding proteins (M1 or PrtF1). Western blots revealed significant induction of α5 integrin and Fn expression by HEp-2 cells in response to TGF-β1. Increased ingestion of streptococci by these cells was blocked by a specific inhibitor of the TGF-β1 receptor I and antibodies directed against α5 integrin and Fn, indicating that increased invasion depends on TGF-β1 up-regulation of both the α5 integrin and Fn. The capacity of TGF-β1 to up-regulate integrin expression and intracellular invasion by GAS was reproduced in primary human tonsil fibroblasts, which could be a source of TGF-β1 in chronically infected tonsils. The relationship between TGF-β1 and GAS invasion was strengthened by the observation that TGF-β1 production was stimulated in GAS-infected primary human tonsil fibroblasts. These findings suggest a mechanism by which GAS induce a cascade of changes in mammalian tissue leading to elevated expression of the α5β1 receptor, enhanced invasion, and increased opportunity for survival and persistence in their human host.
In situ
analysis of nitrogen fixation and metabolic switching in unicellular thermophilic cyanobacteria inhabiting hot spring microbial mats
Authors: Steunou Anne-Soisig , Bhaya Devaki , Bateson Mary M. , Melendrez Melanie C. , Ward David M. , Brecht Eric , Peters John W. , Kühl Michael , Grossman Arthur R.
Published: February 2006

Genome sequences of two
Synechococcus
ecotypes inhabiting the Octopus Spring microbial mat in Yellowstone National Park revealed the presence of all genes required for nitrogenase biosynthesis. We demonstrate that
nif
genes of the
Synechococcus
ecotypes are expressed
in situ
in a region of the mat that varies in temperature from 53.5°C to 63.4°C (average 60°C); transcripts are only detected at the end of the day when the mat becomes anoxic. Nitrogenase activity in mat samples was also detected in the evening. Hitherto, N
2
fixation in hot spring mats was attributed either to filamentous cyanobacteria (not present at >50°C in these mats) or to heterotrophic bacteria. To explore how energy-generating processes of the
Synechococcus
ecotypes track natural light and O
2
conditions, we evaluated accumulation of transcripts encoding proteins involved in photosynthesis, respiration, and fermentation. Transcripts from photosynthesis (
cpcF
,
cpcE
,
psaB
, and
psbB
) and respiration (
coxA
and
cydA
) genes declined in the evening. In contrast, transcripts encoding enzymes that may participate in fermentation fell into two categories; some (
ldh
,
pdhB
,
ald
, and
ackA
) decreased in the evening, whereas others (
pflB
,
pflA
,
adhE
, and
acs
) increased at the end of the day and remained high into the night. Energy required for N
2
fixation during the night may be derived from fermentation pathways that become prominent as the mat becomes anoxic. In a broader context, our data suggest that there are critical regulatory switches
in situ
that are linked to the diel cycle and that these switches alter many metabolic processes within the microbial mat.
An essential role for the hematopoietic transcription factor Ikaros in hypothalamic–pituitary-mediated somatic growth
Authors: Ezzat Shereen , Mader Rene , Fischer Sandra , Yu ShunJiang , Ackerley Cameron , Asa Sylvia L.
Published: February 2006

Ikaros transcription factors play critical functions in the control of lymphohematopoiesis and immune regulation. Family members contain multiple zinc fingers that mediate DNA binding and homooligomerization or heterooligomerization. Ikaros is abundantly expressed in pituitary mammosomatotrophs, where it deacetylates histone 3 sites on the proximal growth hormone (GH) promoter to silence gene expression. Ikaros-null mice display stunted growth with reduced circulating levels of the GH target factor insulin-like growth factor I (IGF-I). Ikaros-deficient mice have small anterior pituitary glands with a disproportionately reduced somatotroph population. Systemic administration of GH results in increased IGF-I levels and enhanced somatic growth. In contrast, reconstitution with WT lymphocytes was not sufficient to rescue the stunted growth phenotype of Ikaros-deficient mice. Ikaros was identified in mouse hypothalamic arcuate nuclei, where it colocalized with GH-releasing hormone (GHRH); in contrast, Ikaros-null mice lack GHRH immunoreactivity in the hypothalamus. Overexpression of Ikaros enhanced GHRH promoter activity and induced endogenous GHRH gene expression. These findings unmask a wider role for Ikaros in the neuroendocrine system, highlighting a critical contribution to the development of the hypothalamic–pituitary somatotrophic axis.
Unraveling the complexity of flux regulation: A new method demonstrated for nutrient starvation in
Saccharomyces cerevisiae
Authors: Rossell Sergio , van der Weijden Coen C. , Lindenbergh Alexander , van Tuijl Arjen , Francke Christof , Bakker Barbara M. , Westerhoff Hans V.
Published: February 2006

An important question is to what extent metabolic fluxes are regulated by gene expression or by metabolic regulation. There are two distinct aspects to this question: (
i
) the local regulation of the fluxes through the individual steps in the pathway and (
ii
) the influence of such local regulation on the pathway’s flux. We developed regulation analysis so as to address the former aspect for all steps in a pathway. We demonstrate the method for the issue of how
Saccharomyces cerevisiae
regulates the fluxes through its individual glycolytic and fermentative enzymes when confronted with nutrient starvation. Regulation was dissected quantitatively into (
i
) changes in maximum enzyme activity (
V
max
, called hierarchical regulation) and (
ii
) changes in the interaction of the enzyme with the rest of metabolism (called metabolic regulation). Within a single pathway, the regulation of the fluxes through individual steps varied from fully hierarchical to exclusively metabolic. Existing paradigms of flux regulation (such as single- and multisite modulation and exclusively metabolic regulation) were tested for a complete pathway and falsified for a major pathway in an important model organism. We propose a subtler mechanism of flux regulation, with different roles for different enzymes, i.e., “leader,” “follower,” or “conservative,” the latter attempting to hold back the change in flux. This study makes this subtlety, so typical for biological systems, tractable experimentally and invites reformulation of the questions concerning the drives and constraints governing metabolic flux regulation.
Prion protein is expressed on long-term repopulating hematopoietic stem cells and is important for their self-renewal
Authors: Zhang Cheng Cheng , Steele Andrew D. , Lindquist Susan , Lodish Harvey F.
Published: February 2006

Although the wild-type prion protein (PrP) is abundant and widely expressed in various types of tissues and cells, its physiological function(s) remain unknown, and PrP knockout mice do not exhibit overt and undisputed phenotypes. Here we showed that PrP is expressed on the surface of several bone marrow cell populations successively enriched in long-term (LT) hematopoietic stem cells (HSCs) using flow cytometry analysis. Affinity purification of the PrP-positive and -negative fractions from these populations, followed by competitive bone marrow reconstitution assays, shows that all LT HSCs express PrP. HSCs from PrP-null bone marrow exhibited impaired self-renewal in serial transplantation of lethally irradiated mouse recipients both in the presence and absence of competitors. When treated with a cell cycle-specific myelotoxic agent, the animals reconstituted with PrP-null HSCs exhibit increased sensitivity to hematopoietic cell depletion. Ectopic expression of PrP in PrP-null bone marrow cells by retroviral infection rescued the defective hematopoietic engraftment during serial transplantation. Therefore, PrP is a marker for HSCs and supports their self-renewal.
N-arachidonoyll-serine, an endocannabinoid-like brain constituent with vasodilatory properties
Authors: Milman Garry , Maor Yehoshua , Abu-Lafi Saleh , Horowitz Michal , Gallily Ruth , Batkai Sandor , Mo Fong-Ming , Offertaler Laszlo , Pacher Pal , Kunos George , Mechoulam Raphael
Published: February 2006

The endocannabinoidN-arachidonoyl ethanolamine (anandamide), found both in the CNS and in the periphery, plays a role in numerous physiological systems. One might expect that the chemically relatedN-arachidonoyl-l-serine (ARA-S) could also be formed alongside anandamide. We have now isolated ARA-S from bovine brain and elucidated its structure by comparison with synthetic ARA-S. Contrary to anandamide, ARA-S binds very weakly to cannabinoid CB1and CB2or vanilloid TRPV1 (transient receptor potential vanilloid 1) receptors. However, it produces endothelium-dependent vasodilation of rat isolated mesenteric arteries and abdominal aorta and stimulates phosphorylation of p44/42 mitogen-activated protein (MAP) kinase and protein kinase B/Akt in cultured endothelial cells. ARA-S also suppresses LPS-induced formation of TNF-α in a murine macrophage cell line and in wild-type mice, as well as in mice deficient in CB1or CB2receptors. Many of these effects parallel those reported for abnormal cannabidiol (Abn-CBD), a synthetic agonist of a putative novel cannabinoid-type receptor. Hence, ARA-S may represent an endogenous agonist for this receptor.
Guanosine 3′,5′-bispyrophosphate coordinates global gene expression during glucose-lactose diauxie in
Escherichia coli
Authors: Traxler Matthew F. , Chang Dong-Eun , Conway Tyrrell
Published: February 2006

Guanosine 3′,5′-bispyrophosphate (ppGpp), also known as “magic spot,” has been shown to bind prokaryotic RNA polymerase to down-regulate ribosome production and increase transcription of amino acid biosynthesis genes during the stringent response to amino acid starvation. Because many environmental growth perturbations cause ppGpp to accumulate, we hypothesize ppGpp to have an overarching role in regulating the genetic program that coordinates transitions between logarithmic growth (feast) and growth arrest (famine). We used the classic glucose-lactose diauxie as an experimental system to investigate the temporal changes in transcription that accompany growth arrest and recovery in wild-type
Escherichia coli
and in mutants that lack RelA (ppGpp synthetase) and other global regulators, i.e., RpoS and Crp. In particular, diauxie was delayed in the
relA
mutant and was accompanied by a 15% decrease in the number of carbon sources used and a 3-fold overall decrease in the induction of RpoS and Crp regulon genes. Thus the data significantly expand the previously known role of ppGpp and support a model wherein the ppGpp-dependent redistribution of RNA polymerase across the genome is the driving force behind control of the stringent response, general stress response, and starvation-induced carbon scavenging. Our conceptual model of diauxie describes these global control circuits as dynamic, interconnected, and dependent upon ppGpp for the efficient temporal coordination of gene expression that programs the cell for transitions between feast and famine.
Identification and characterization of a gonadotropin-inhibitory system in the brains of mammals
Authors: Kriegsfeld Lance J. , Mei Dan Feng , Bentley George E. , Ubuka Takayoshi , Mason Alex O. , Inoue Kazuhiko , Ukena Kazuyoshi , Tsutsui Kazuyoshi , Silver Rae
Published: February 2006

Successful reproduction requires maintenance of the reproductive axis within fine operating limits through negative feedback actions of sex steroids. Despite the importance of this homeostatic process, our understanding of the neural loci, pathways, and neurochemicals responsible remain incomplete. Here, we reveal a neuropeptidergic pathway that directly links gonadal steroid actions to regulation of the reproductive system. An RFamide (Arg-Phe-NH
2
) peptide that inhibits gonadotropin release from quail pituitary was recently identified and named gonadotropin-inhibitory hormone (GnIH). Birds are known to have specialized adaptations associated with gonadotropin-releasing hormone (GnRH) regulation to optimize reproduction (e.g., encephalic photoreceptors), and the existence of a hypothalamic peptide inhibiting gonadotropins may or may not be another such specialization. To determine whether GnIH serves as a signaling pathway for sex steroid regulation of the reproductive axis, we used immunohistochemistry and
in situ
hybridization to characterize the distribution and functional role of this peptide in hamsters, rats, and mice. GnIH-immunoreactive (GnIH-ir) cell bodies are clustered in the mediobasal hypothalamus with pronounced projections and terminals throughout the CNS.
In vivo
GnIH administration rapidly inhibits luteinizing hormone secretion. Additionally, GnIH-ir neurons form close appositions with GnRH cells, suggesting a direct means of GnRH modulation. Finally, GnIH-ir cells express estrogen receptor-α and exhibit robust immediate early gene expression after gonadal hormone stimulation. Taken together, the distribution of GnIH efferents to neural sites regulating reproductive behavior and neuroendocrine secretions, expression of steroid receptors in GnIH-ir nuclei, and GnIH inhibition of luteinizing hormone secretion indicate the discovery of a system regulating the mammalian reproductive axis.
Ataxia telangiectasia mutated (Atm) is not required for telomerase-mediated elongation of short telomeres
Authors: Feldser David , Strong Margaret A. , Greider Carol W.
Published: February 2006

Telomerase-mediated telomere addition counteracts telomere shortening due to incomplete DNA replication. Short telomeres are the preferred substrate for telomere addition by telomerase; however, the mechanism by which telomerase recognizes short telomeres is unclear. In yeast, the Ataxia telangiectasia mutated (Atm) homolog, Tel1, is necessary for normal telomere length regulation likely by altering telomere structure, allowing telomerase recruitment to short telomeres. To examine the role of Atm in establishing preference for elongation of short telomeres in mice, we examined telomerase-mediated elongation of short dysfunctional telomeres in the presence or absence of Atm. Here we show that Atm is dispensable for elongation of short telomeres by telomerase, suggesting that telomerase recruitment in mammalian cells and in yeast may be regulated differently.
Nurses and Occupational Exposures to Bloodborne Viruses in Poland
Authors: Gańczak Maria , Milona Marta , Szych Zbigniew
Published: February 2006

Study Objective.

To record descriptions of occupational exposures to blood, determine factors predictive of exposure, and identify interventions that might reduce the frequency of exposure.

Design.

An analytic, cross-sectional survey.

Study Population.

A total of 601 nurses from surgical wards, operating rooms, and emergency departments.

Study Instrument.

An anonymous questionnaire developed by the authors on the basis of previously published guidelines was distributed between January and March 2003.

Sampling.

Random, with 18 hospitals selected from 2 urban and rural locations.

Results.

Almost half of respondents reported having had at least 1 puncture injury during the preceding year, 1 in 5 had exposure via mucous membranes, and more than half had worked at least once with a recent abrasion or cut on their hands. The number of injuries was independent of age (P = .26), duration of practice (P = .21), and workplace setting (P = .78). The percentage of nurses without percutaneous exposure during the preceding year was significantly higher in the group that received special HIV/AIDS training than in the group that did not (95% confidence interval, 5.8-24.1%; P<.002). The most recent exposure was primarily caused by hollow-bore needles, involved the palm and fingers II-V, was self-inflicted, took place during an elective procedure, and was not reported to the hospital's infection control center by 74% of respondents. The most common reason for not reporting the exposure (38% of cases) was the conviction that the source patient was not infected.

Conclusions.

Because of the large number of occupational exposures to blood, especially those due to injuries with hollow-bore needles, nurses should adopt more adequate behavioral strategies to prevent the transmission of blood-borne pathogens. Policies for providing adequate education programs tailored to encourage nurses to report all exposures are urgently required.
Molecular Epidemiology ofStaphylococcus aureusColonization in 2 Long-Term Care Facilities
Authors: Mody Lona , Flannery Erica , Bielaczyc Andrew , Bradley Suzanne F.
Published: February 2006

Persistent colonization withStaphylococcus aureuswas assessed in 22 nursing home residents. Eighteen residents (82%) remained colonized with the same strain found at baseline; 6 (33%) of 18 residents transiently acquired a new strain. Four residents (18%) acquired a new persistent strain. Residents colonized with methicillin-resistantS. aureuswere more likely to acquire a new strain (67%) than were residents colonized with methicillin-susceptibleS. aureus(20%) (P= .04).
Methicillin-ResistantStaphylococcus aureusin German Intensive Care Units During 2000-2003: Data from Project SARI (Surveillance of Antimicrobial Use and Antimicrobial Resistance in Intensive Care Units)
Authors: Meyer Elisabeth , Schwab Frank , Gastmeier Petra , Jonas Daniel , Rueden Henning , Daschner Franz D.
Published: February 2006

Objectives.

The objective of this study was to analyze methicillin-resistantStaphylococcus aureus(MRSA) percentages (defined as the percentage ofS. aureusisolates that are resistant to methicillin) and antimicrobial consumption in intensive care units (ICUs) participating in Project SARI (Surveillance of Antimicrobial Use and Antimicrobial Resistance in Intensive Care Units), to look for temporal changes in MRSA percentages and antimicrobial consumption in individual ICUs as an indicator of the impact of an active surveillance system, and to investigate the differences between ICUs with increased MRSA percentages versus those with decreased percentages during a period of 3 years (2001-2003).

Methods.

This was a prospective, ICU-based and laboratory-based surveillance study involving 38 German ICUs during 2000-2003. Antimicrobial use was reported in terms of defined daily doses (DDDs) per 1,000 patient-days. Temporal changes in the MRSA percentage and antimicrobial use in individual ICUs were calculated by means of the Wilcoxon signed rank test. The incidence density of nosocomial MRSA infection was defined as the number of nosocomial MRSA infections per 1,000 patient-days.

Results.

From February 2000 through December 2003, a total of 38 ICUs reported data on 499,694 patient-days and 9,552S. aureusisolates, including 2,249 MRSA isolates and 660,029 DDDs of antimicrobials. Cumulative MRSA percentages ranged from 0% to 64.4%, with a mean of 23.6%. The MRSA incidence density ranged from 0 to 38.2 isolates per 1,000 patient-days, with a mean of 2.77 isolates per 1,000 patient-days. There was a positive correlation between MRSA percentage and imipenem and ciprofloxacin use (P<.05). Overall, comparison of data from 2001 with data from 2003 showed that MRSA percentages increased in 18 ICUs (median increase, 13.2% [range, 1.6%-38.4%]) and decreased in 14 ICUs (median decrease, 12% [range, 1.0%-48.4%]). Increased use of third-generation cephalosporins, glycopeptides, or aminoglycosides correlated significantly with an increase in the MRSA percentage (P<.05). The cumulative nosocomial MRSA infection incidence density for 141 ICUs that did not participate in SARI and, therefore, did not receive feedback increased from 0.26 to 0.35 infections per 1,000 patient-days during a 3-year period, whereas the rate in SARI ICUs decreased from 0.63 to 0.40 infections per 1,000 patient-days.

Conclusion.

The MRSA situation in German ICUs is still heterogeneous. Because MRSA percentages range from 0% to 64.4%, further studies are required to confirm findings that no change in the MRSA percentage and a decrease in the nosocomial MRSA infection incidence density in SARI ICUs reflect the impact of an active surveillance system.
Biofilm Formation by and Accessory Gene Regulator Typing of Methicillin-ResistantStaphylococcus aureusStrains Recovered From Patients With Nosocomial Infections
Authors: Manago Kunihiro , Nishi Junichiro , Wakimoto Naoko , Miyanohara Hiroaki , Sarantuya Jav , Tokuda Koichi , Iwashita Mayumi , Yamamoto Kimie , Yoshinaga Masao , Maruyama Ikuro , Kawano Yoshifumi
Published: February 2006

The association between biofilm formation and the accessory gene regulator (agr) types of methicillin-resistantStaphylococcus aureus(MRSA) strains in our hospital were investigated. The biofilm index and the incidence of MRSA strains carryingagr-2in the infection group (n= 91) were significantly higher than were those in the carrier group (n= 225), suggesting that biofilm formation andagrtype are associated with nosocomial MRSA infections.
What Proportion of Hospital Patients Colonized With Methicillin-ResistantStaphylococcus aureusAre Identified by Clinical Microbiological Cultures?
Authors: Salgado Cassandra D. , Farr Barry M.
Published: February 2006

Background.

Most hospitals in the United States do not perform active surveillance cultures and, thus, rely on clinical microbiological cultures (CMCs) to identify patients colonized with methicillin-resistantStaphylococcus aureus(MRSA). We sought to determine what proportion of patients who are colonized with MRSA at admission are identified by CMCs during hospitalization.

Methods.

From February 1998 through November 2002, patients found to be colonized with MRSA at admission by use of active surveillance cultures were identified. The proportion of colonized patients who had a CMC that was positive for MRSA, the number of CMCs performed and their type (ie, according to the anatomical site from which specimens were obtained for culture), and the number and type of CMCs that were positive for MRSA were calculated.

Results.

Four hundred thirty-seven patients were found to be colonized with MRSA at admission, and 98 of 1,238 CMCs (7.9%; 95% confidence interval, 6.5%-9.6%) performed for 66 of these patients (15%; 95% confidence interval, 11.9%-18.8%) were positive for MRSA. The number of nonisolated days that would have occurred by relying on CMCs to identify MRSA-colonized patients was 3,247 (mean, 7.4 days per patient). Among the anatomical sites from which specimens were obtained for CMC, wounds demonstrated the highest sensitivity (30.2%) for identifying MRSA-colonized patients.

Conclusions.

CMCs failed to identify 85% of MRSA-colonized patients, because, in part, CMCs identified only a small proportion of colonized patients. Because many studies have shown a decrease in the transmission of MRSA from colonized patients for whom contact precautions, rather than standard precautions, are used, the findings of this study suggest that failure to identify colonized patients and to use contact precautions may be an important reason for the increasing rate of nosocomial MRSA infection in hospitals in the United States.
Reduction in Inddence of Nosocomial Methicillin-Resistant Staphylococcus aureus (MRSA) Infection in an Intensive Care Unit: Role of Treatment With Mupirocin Ointment and Chlorhexidine Baths for Nasal Carriers of MRSA
Authors: Sandri Ana Maria , Dalarosa Micheline Gisele , Alcântara Luciana Ruschel de , Elias Laura da Silva , Zavascki Alexandre Prehn
Published: February 2006

After the introduction of routine treatment for every nasal carrier of methicillin-resistant Staphylococcus aureus, active follow-up surveillance for nosocomial methicillin-resistant S. aureus infection was conducted for 5 years in an intensive care unit of a tertiary-care teaching hospital. There was a significant decrease in the incidence of nosocomial methicillin-resistant S. aureus infection during the later years of follow-up. Decolonization of nasal carriers of methicillin-resistant S. aureus is probably associated with such findings.