bluuebunny/crossref_metadata_2025 huggingface dataset:
Au
∕
Ag
and Au∕Pd molecular contacts to GaAs
Authors: Ahktari-Zavareh Azadeh , Li Wenjie , Kavanagh Karen L. , Trionfi Aaron J. , Jones Jason C. , Reno John L. , Hsu Julia W. P. , Talin A. Alec
Published: August 2008

The hot electron transport through Au∕Pd or Au∕Ag/molecular layer/n-GaAs diodes has been studied by using ballistic electron emission microscopy (BEEM). The monolayers consisted of either octanedithiol (HS–(CH2)8–SH) or hexadecanethiol (HS–(CH2)15–CH3) linear alkane chains and were deposited from ethanol solutions onto molecular beam epitaxially grown GaAs (001) surfaces. The metals were electron-beam evaporated onto the molecular layer. Similar to previous results for Au diodes, Au∕Pd metallization onto an octanedithiol monolayer resulted in a large reduction in the BEEM signal, compared to Au and Au∕Pd reference diodes (without monolayers). However, unlike Au/octanedithiol diodes, the BEEM signal was stronger and the threshold was found to be 1.2eV instead of 1.4eV. We attribute this to ballistic electron transmission rather than to the photonic signal that we previously reported for Au/octanedithiol. In comparison, the Au∕Pd/hexadecanethiol diodes showed little change from the reference Au∕Pd diodes, suggesting monolayer disruption by interdiffusion of Pd or Au through the molecules to the interface. Ag∕GaAs or Au∕Ag∕GaAs diodes, with or without a molecular layer, did not result in reliable tunneling, likely the result of a tip-induced reaction. The octanedithiol layer on GaAs provides a free thiol group for bonding with the top metal contact, minimizing Au or Pd penetration and the displacement of the molecule-GaAs thiol bond but not completely eliminating these effects in the case of Pd.
Magnetocapacitance effect in InMnAs∕InAs p-n heterojunctions
Authors: Rangaraju N. , Wessels B. W.
Published: August 2008

The magnetocapacitance characteristics of an epitaxial p-n heterojunction between magnetic InMnAs and InAs are investigated. A large positive magnetocapacitance is observed at room temperature, which increases with reverse bias. For high reverse bias, the magnetocapacitance is linearly dependent on magnetic field. From capacitance-voltage measurements, the junction built-in voltage was determined and was observed to increase with magnetic field. The magnetocapacitance measurements support a model for a magnetic semiconductor heterojunction where spin-split polarized valence and conduction bands form due to the giant Zeeman effect.
Surface roughness generated by plasma etching processes of silicon
Authors: Martin M. , Cunge G.
Published: August 2008

The authors used atomic force microscopy to analyze the roughness generated on c-Si (100) surfaces when etched in high-density plasmas over a wide range of conditions (pressure, rf power) using SF6, CF4, Cl2, and HBr chemistries. The authors demonstrate unambiguously that high-density plasmas do not generate roughness during silicon etching; but on the contrary, they tend to smooth the existing surface roughness if already present. This is evidenced by analyzing the time evolution of the shape of self-organized silicon nanopillars (patterned on the Si wafer by using diblock copolymers as an etch mask). The 20-nm-high, 20-nm-wide pillars separated by 10nm are rapidly smoothed by exposure to Cl2 and SF6 plasmas, thus restoring a flat silicon surface. In high-density plasmas, the local etch rate is generally limited by the availability of reactive radicals. In these conditions, the smoothing mechanism is due to the fact that the hills of a rough surface receive a higher flux of etchant radicals than the valleys. Finally, the authors show that the roughening of silicon surfaces in F-based plasma, often reported in the literature, is only due to the micromasking of silicon by AlFx particles originating from the sputtering of the (Al2O3) reactor walls. A high percentage of Al is indeed detected on the surface after etching in F-based plasmas. However, when the chamber walls are intentionally coated by a carbon layer prior to the silicon etching process, the F-based plasmas behave like the other etching chemistries investigated: they rapidly smooth any existing roughness.
Characteristics of lanthanum hafnium oxide deposited by electron cyclotron resonance atomic layer deposition
Authors: Kim Woong-Sun , Kim Tae-Sub , Kang Byung-Woo , Ko Myoung-Gyun , Park Sang-Kyun , Park Jong-Wan
Published: August 2008

Lanthanum hafnium oxide (LHO) thin films were grown using an electron cyclotron resonance atomic layer deposition technique. Tetrakis(ethylmethylamino)hafnium (TEMAHf) and tris(ethylcyclopentadienyl) lanthanum (III) [La(EtCp)3] were utilized as the hafnium and lanthanum precursors, respectively. O2 plasma was used as a reactant gas. Transmission electron microscopy analyses revealed that the as-deposited LHO film had a crystalline structure at a deposition temperature of 400°C. Rapid thermal annealing of the LHO films induced dramatic changes in the electrical properties. The VFB for the films shifted toward the ideal VFB and the amount of positive fixed charge disappeared in the LHO films. The leakage current density of the film deposited at 400°C was estimated to be 4.6×10−7A∕cm2 at −1V. The leakage characteristic of the LHO films was improved with annealing at temperatures above 900°C.
Nickel and nickel silicide Schottky barrier contacts to n-type silicon nanowires
Authors: Woodruff S. M. , Dellas N. S. , Liu B. Z. , Eichfeld S. M. , Mayer T. S. , Redwing J. M. , Mohney S. E.
Published: August 2008

Schottky contacts to n-type silicon nanowires were fabricated using Ni or nickel silicide contacts in a wraparound or end contact geometry, respectively. Series resistance in the test structures was reduced by heavily doping the opposite end of the silicon nanowire, facilitating Ohmic contact formation and reducing the resistance of the nanowire itself. The effective Schottky barrier height is reported as a function of nanowire doping, ambient, and applied back gate bias, highlighting some of the important variables affecting current transport in Schottky contacts to semiconductor nanowires. For the silicide contact to the most lightly doped silicon nanowire, measurements in N2 showed that the effective barrier height without a back gate bias was 0.69 eV, and the ideality factor was 1.1.
Metal-containing release layers for use with UV-cure nanoimprint lithographic template materials
Authors: Houle F. A. , Raoux S. , Miller D. C. , Jahnes C. , Rossnagel S.
Published: August 2008

Ultrathin films of amorphous metal oxides and nitrides are evaluated as potential release coatings for UV-cure nanoimprint templates in combination with diverse resist chemistries. Although adhesive behaviors cover a broad range, when paired with a compatible resist use of a metal containing release layer allows adhesion energies approaching the van der Waals limit, with clean fracture at the resist release layer interface, to be obtained. These films provide an alternative to the more commonly used fluoroalkyl silanes and other release treatments.
Stable field emission from screen-printed ZnO-tetrapod emitters
Authors: Hou Kai , Li Chi , Lei Wei , Zhang Xiaobing , Qu Ke , Yang Xiaxi , Zhao Zhiwei , Wang Baoping
Published: August 2008

This article describes a study on field emission properties of ZnO tetrapods, which were synthesized by rapid heating metal zinc pellets at 900°C in air. A diode configuration with a screen-printed cathode was used to measure the field emission properties of the ZnO emitters. A low turn-on field of 1.86V∕μm at a current density of 1μA∕cm2 was obtained, while the emission current density reached 1mA∕cm2 at an applied field of 4.15V∕μm and showed no saturation. The field emission of the ZnO-tetrapod sample was recorded for 20h: no degradation of the emission current was observed in this period, while the fluctuations of the emission current were less than 3%. These experimental results indicate that ZnO tetrapods are a promising cold cathode for low cost field emission displays using screen printing.
Highly efficient vertical outgassing channels for low-temperature InP-to-silicon direct wafer bonding on the silicon-on-insulator substrate
Authors: Liang D. , Bowers J. E.
Published: August 2008

The authors report a highly efficient design for low-temperature, void-free InP-to-silicon direct wafer bonding on a silicon-on-insulator (SOI) substrate. By etching an array of small through holes in the top silicon layer, the generated gas by-products (H2O, H2) from bonding polymerization reactions and thus gaseous hydrocarbon can be absorbed and diffuse in the buried oxide layer, resulting in up to five orders of magnitude interfacial void density reduction (from >50 000 to ≤3 cm−2). The required annealing time is reduced to less than 30 min, a ∼100X improvement compared to the previous outgassing design as well. Comprehensive studies in associated processing details, bonding surface energy, universality, and stability are also presented. Successful 50, 75, and 100 mm InP expitaxial layer transfer to the SOI substrate is also demonstrated, which indicates a total elimination of outgassing issues regardless of the wafer bonding dimension. Several incidental advantages leading to a flexible device design, low fabrication cost, and potential bonding strain relief are also discussed.
Interaction of microwaves with photoelectrons in semiconductors
Authors: Ahrenkiel R. K. , Johnston S. W.
Published: August 2008

Microwave photoconductive decay is widely used to measure the recombination lifetime in semiconductors and is generally considered to be a low-injection technique. Here, the authors examine the technique in detail from both a theoretical and experimental perspective. When the skin or penetration depth is much less than the sample thickness, the reflectance-conductivity relationship is nonlinear when the injected carrier density exceeds about 5% of background doping. However, when the penetration depth is much larger than the sample thickness, the transmitted signal is linear over several orders of magnitude of sample conductivity. In the transmission mode of operation, high-injection lifetime measurements are accurate.
Interfacial and electrical properties of ZrxTi1−xO4 (x=0.66) films deposited by liquid-delivery metal organic chemical vapor deposition to be used as high-k gate dielectric
Authors: Sahu B. S. , Pammi S. V. N. , Seong Nak-Jin , Yoon Soon-Gil
Published: August 2008

Zr x Ti 1 − x O 4  (x=0.66) films were deposited on p-type Si (100) substrate using liquid-delivery metal organic chemical vapor deposition using Zr(O–C3H7)2{(C11H19O2)2} and Ti(O–C3H7)2{(C11H19O2)2} precursors. Postdeposition rapid thermal annealing was performed in N2 ambient to improve the electrical characteristics of the films. The postdeposition annealed samples show excellent electrical characteristics, such as low values of effective oxide charge density, flatband voltage, hysteresis, oxide trap charge density, and interface state density. No metal silicides were found in the films. A minimum leakage current density of the order of ∼10−5A∕cm2 at a bias voltage of −1V has been obtained even after annealing at 800°C.
Metal nanoparticle embedded porous thin films prepared by oblique angle coevaporation
Authors: Blackwell R. , Zhao Y.-P.
Published: August 2008

Using oblique angle coevaporation, the authors have successfully incorporated Ag nanoparticles into MgF2 porous films. The size of the embedded Ag nanoparticles and the porosity of MgF2 host increase with increasing vapor incident angle, resulting in a redshift in the plasmon resonant wavelength of the Ag nanoparticles. The optical properties of the composite films also depend on the ratio of MgF2 and Ag, the film thickness, and the host porosity. This method can be used to fine-tune the plasmon absorbance peaks of metal-insulator composite thin films, and have potential applications in optical devices and chemical and biological sensing.
Ti
∕
Ni
bilayer Ohmic contact on 4H-SiC
Authors: Ohyanagi Takasumi , Onose Yasuo , Watanabe Atsuo
Published: August 2008

Electric contact properties and interface structures of titanium/nickel (Ti∕Ni) bilayer Ohmic contact and the aluminum (Al) overlay on 4H silicon carbide (4H-SiC) were investigated. The Al overlay was used for wiring and bonding pads to pass high currents, and usually deposited after the high temperature annealing of the Ohmic contact. We found that the adhesion between the Ti∕Ni Ohmic contact and the Al overlay was improved compared to that of the Ni Ohmic contact and the Al overlay. Auger electron spectroscopy depth profiles showed that in the case of the Ti∕Ni Ohmic contacts, titanium carbide (TiC) exists at the interface between Ni silicide and the Al overlay. This TiC leads the Al to diffuse into the Ni-silicide layer, and the adhesion between Ni silicide and the Al is improved. Moreover, the authors compared the contact resistance before/after 500°C annealing after the Al deposition, and the authors found that the contact resistance was affected by the interface carbon structures.
Quantum ring formation and antimony segregation in GaSb∕GaAs nanostructures
Authors: Timm R. , Lenz A. , Eisele H. , Ivanova L. , Dähne M. , Balakrishnan G. , Huffaker D. L. , Farrer I. , Ritchie D. A.
Published: August 2008

GaSb quantum rings in GaAs were studied by cross-sectional scanning tunneling microscopy. The quantum rings have an outer shape of a truncated pyramid with typical lateral extensions between 10 and 30nm and heights between 1 and 3nm, depending on the molecular beam epitaxy growth conditions. A clear central opening of varying diameter and more or less conical shape, filled with GaAs, is characteristic for the GaSb rings. The self-organized formation of quantum rings during the growth and subsequent fast overgrowth of GaSb quantum dots is attributed to a combination of large strain with strong Sb segregation. The latter is enabled by extensive group-V atomic exchange reactions at the GaSb∕GaAs interfaces, which are quantitatively evaluated from the atomically resolved microscopy data.
Interfacial effects in thin films of polymeric semiconductors
Authors: Rivnay Jonathan , Jimison Leslie H. , Toney Michael F. , Preiner Michael , Melosh Nicholas A. , Salleo Alberto
Published: August 2008

The surface onto which polymeric semiconductors are cast from solution plays an important role in determining the electrical transport properties of the polymeric thin film. The authors use synchrotron-based x-ray diffraction to show that even moderate roughness (rms∼5 Å) can affect the texture of semicrystalline poly(thiophene) thin films. Moreover, the authors use a novel optical characterization technique (surface plasmon resonance spectroscopy) to characterize the appearance of electronic states in the bandgap of thin films (∼20 nm) of regioregular poly(thiophene). Such states may be due to the heterointerface between the thin Au substrate and the polymer.
Gas-assisted focused electron beam and ion beam processing and fabrication
Authors: Utke Ivo , Hoffmann Patrik , Melngailis John
Published: August 2008

Beams of electrons and ions are now fairly routinely focused to dimensions in the nanometer range. Since the beams can be used to locally alter material at the point where they are incident on a surface, they represent direct nanofabrication tools. The authors will focus here on direct fabrication rather than lithography, which is indirect in that it uses the intermediary of resist. In the case of both ions and electrons, material addition or removal can be achieved using precursor gases. In addition ions can also alter material by sputtering (milling), by damage, or by implantation. Many material removal and deposition processes employing precursor gases have been developed for numerous practical applications, such as mask repair, circuit restructuring and repair, and sample sectioning. The authors will also discuss structures that are made for research purposes or for demonstration of the processing capabilities. In many cases the minimum dimensions at which these processes can be realized are considerably larger than the beam diameters. The atomic level mechanisms responsible for the precursor gas activation have not been studied in detail in many cases. The authors will review the state of the art and level of understanding of direct ion and electron beam fabrication and point out some of the unsolved problems.
Interface structure and transport of complex oxide junctions
Authors: Nelson-Cheeseman B. B. , Wong F. , Chopdekar R. V. , Chi M. , Arenholz E. , Browning N. D. , Suzuki Y.
Published: August 2008

The interface structure and magnetism of hybrid magnetic tunnel junction-spin filter devices have been investigated and correlated with their transport properties. Magnetic tunnel junctions made of a spinel NiMn2O4 tunnel barrier sandwiched by theoretically predicted half-metallic electrodes, perovskite La0.7Sr0.3MnO3 and spinel Fe3O4, exhibit very high crystalline quality as observed by transmission electron microscopy. Structurally abrupt interfaces allow for the distinct magnetic switching of the electrodes as well as large junction magnetoresistance. The change in the magnetic anisotropy observed at the spinel-spinel interface is indicative of a thin interdiffused magnetically soft interfacial layer. The strong exchange coupling at this interface allows for low background magnetoresistance, and a spin-filter effect with when the barrier is ferrimagnetic.
Imaging classical and quantum structures in an open quantum dot using scanning gate microscopy
Authors: Burke A. M. , Aoki N. , Akis R. , Ochiai Y. , Ferry D. K.
Published: August 2008

The authors present scanning gate microscopy (SGM) measurements of an in-plane gated open quantum dot and relate structures within the measurement to a theoretical calculation of the change in conductance in a similar dot. The dot was fabricated in GaAs/AlGaAs. Electron beam lithography and wet etching were used to isolate the two dimensional electron gas and form the device geometry. The SGM image was then high-pass filtered to show both classical and quantum behavior and similarities to a calculated structure are suggested.
A study of patterning and annealing effects on the performance of magnetic planar inductor
Authors: Sun Hongfang , Liu Zewen , Zhao Jiahao , Wang Li , Zhu Jing
Published: August 2008

Study on the patterning and annealing effect of planar inductors with composite ferromagnetic films has been presented in this article. The magnetic films (MFs) are deposited on the same coil structure and then followed by an annealing process in vacuum. Two equivalent circuits are proposed to analyze the modification of inductor performance. The patterned inductors exhibit higher quality factor without much decrease of inductance compared with the nonpatterned one. The square-type inductor shows the highest peak value of quality factor (16.01 at 1.15GHz) because of the finest MF division. After annealing, both the inductance and quality factor of the four types of inductors are increased, and the nonpatterned inductor shows the largest increment of inductance.
High sensitivity cantilevers for measuring persistent currents in normal metal rings
Authors: Bleszynski-Jayich A. C. , Shanks W. E. , Ilic B. R. , Harris J. G. E.
Published: August 2008

The authors propose a new approach to measuring persistent currents in normal metal rings. By integrating micron-scale metal rings into sensitive micromechanical cantilevers and using the cantilevers as torque magnetometers, it should be possible to measure the rings’ persistent currents with greater sensitivity than the superconducting quantum interference device based and microwave resonator-based detectors used in the past. In addition, cantilever-based detectors may allow for measurements in a cleaner electromagnetic environment. The authors have fabricated ultrasensitive cantilevers with integrated rings and measured their mechanical properties. The authors present an estimate of the persistent current sensitivity of these cantilever-based detectors, focusing on the limits set by the cantilever’s Brownian motion and the shot noise in the laser interferometer that monitors the cantilever.
Electrical characteristics of Pt∕Au Schottky contacts to plasma-etched AlGaN
Authors: Syed A. A. , Cao X. A. , Woodworth A. A. , Stinespring C. D.
Published: August 2008

The effects of surface treatment using Ar and Cl2∕BCl3 inductively coupled plasmas on the rectifying characteristics of Pt∕Au contacts to AlxGa1−xN (x=0.1–0.5) were investigated. Plasma treatment increased the conductivity of Al0.1Ga0.9N surfaces, making the rectifying contacts into Ohmic contacts. For higher Al-content AlGaN, the Schottky diodes turned leaky after Cl2∕BCl3 plasma treatment, where damage creation and etching occur simultaneously, whereas the diodes become more rectifying upon Ar plasma exposure, in which plasma damage accumulates. A time-dependent study of Ar plasma treatment supports the hypothesis that the energy level of plasma damage in high-Al content AlGaN may be damage density dependent, and damage accumulation during Ar plasma exposure results in a high-resistivity region compensated by deep-level defect states.
Heterochromatin Integrity Affects Chromosome Reorganization After Centromere Dysfunction
Authors: Ishii Kojiro , Ogiyama Yuki , Chikashige Yuji , Soejima Saeko , Masuda Fumie , Kakuma Tatsuyuki , Hiraoka Yasushi , Takahashi Kohta
Published: August 2008

The centromere is essential for the inheritance of genetic information on eukaryotic chromosomes. Epigenetic regulation of centromere identity has been implicated in genome stability, karyotype evolution, and speciation. However, little is known regarding the manner in which centromere dysfunction affects the chromosomal architectures. Here we show that in the fission yeast
Schizosaccharomyces pombe
, the conditional deletion of the centromere produces survivors that carry either a neocentromere-acquired chromosome at the subtelomeric region or an acentric chromosome rescued by intertelomere fusion with either of the remaining chromosomes. The ratio of neocentromere formation to telomere fusion is considerably decreased by the inactivation of genes involved in RNA interference–dependent heterochromatin formation. By affecting the modes of chromosomal reorganization, the genomic distribution of heterochromatin may influence the fate of karyotype evolution.
A Stable Silicon(0) Compound with a Si=Si Double Bond
Authors: Wang Yuzhong , Xie Yaoming , Wei Pingrong , King R. Bruce , Schaefer Henry F. , von R. Schleyer Paul , Robinson Gregory H.
Published: August 2008

Dative, or nonoxidative, ligand coordination is common in transition metal complexes; however, this bonding motif is rare in compounds of main group elements in the formal oxidation state of zero. Here, we report that the potassium graphite reduction of the neutral hypervalent silicon-carbene complex L:SiCl
4
{where L: is:C[N(2,6-Pr
i
2
-C
6
H
3
)CH]
2
and Pr
i
is isopropyl} produces L:(Cl)Si–Si(Cl):L, a carbene-stabilized bis-silylene, and L:Si=Si:L, a carbene-stabilized diatomic silicon molecule with the Si atoms in the formal oxidation state of zero. The Si-Si bond distance of 2.2294 ± 0.0011 (standard deviation) angstroms in L:Si=Si:L is consistent with a Si=Si double bond. Complementary computational studies confirm the nature of the bonding in L:(Cl)Si–Si(Cl):L and L:Si=Si:L.
Automatic Mental Associations Predict Future Choices of Undecided Decision-Makers
Authors: Galdi Silvia , Arcuri Luciano , Gawronski Bertram
Published: August 2008

Common wisdom holds that choice decisions are based on conscious deliberations of the available information about choice options. On the basis of recent insights about unconscious influences on information processing, we tested whether automatic mental associations of undecided individuals bias future choices in a manner such that these choices reflect the evaluations implied by earlier automatic associations. With the use of a computer-based, speeded categorization task to assess automatic mental associations (i.e., associations that are activated unintentionally, difficult to control, and not necessarily endorsed at a conscious level) and self-report measures to assess consciously endorsed beliefs and choice preferences, automatic associations of undecided participants predicted changes in consciously reported beliefs and future choices over a period of 1 week. Conversely, for decided participants, consciously reported beliefs predicted changes in automatic associations and future choices over the same period. These results indicate that decision-makers sometimes have already made up their mind at an unconscious level, even when they consciously indicate that they are still undecided.
Observation of Atomic Diffusion at Twin-Modified Grain Boundaries in Copper
Authors: Chen Kuan-Chia , Wu Wen-Wei , Liao Chien-Neng , Chen Lih-Juann , Tu K. N.
Published: August 2008

Grain boundaries affect the migration of atoms and electrons in polycrystalline solids, thus influencing many of the mechanical and electrical properties. By introducing nanometer-scale twin defects into copper grains, we show that we can change the grain-boundary structure and atomic-diffusion behavior along the boundary. Using in situ ultrahigh-vacuum and high-resolution transmission electron microscopy, we observed electromigration-induced atomic diffusion in the twin-modified grain boundaries. The triple point where a twin boundary meets a grain boundary was found to slow down grain-boundary and surface electromigration by one order of magnitude. We propose that this occurs because of the incubation time of nucleation of a new step at the triple points. The long incubation time slows down the overall rate of atomic transport.
Detection of an Antigenic Group 2 Coronavirus in an Adult Alpaca with Enteritis
Authors: Genova Suzanne G. , Streeter Robert N. , Simpson Katharine M. , Kapil Sanjay
Published: August 2008

Antigenic group 2 coronavirus was detected in a fecal sample of an adult alpaca by reverse transcription-PCR. The presence of alpaca coronavirus (ApCoV) in the small intestine was demonstrated by immune histochemistry with an antinucleocapsid monoclonal antibody that reacts with group 2 coronaviruses. Other common causes of diarrhea in adult camelids were not detected. We conclude that nutritional stress may have predisposed the alpaca to severe ApCoV infection.
Validation of Cultivation and PCR Methods for Diagnosis of Lyme Neuroborreliosis
Authors: Cerar Tjaša , Ogrinc Katarina , Cimperman Jože , Lotrič-Furlan Stanka , Strle Franc , Ružić-Sabljić Eva
Published: August 2008

Borrelial infection may manifest with a wide range of clinical signs, and in many cases, microbiological findings are essential for a proper diagnosis. This study included 48 patients with a working clinical diagnosis of Lyme neuroborreliosis, 45 patients with a working clinical diagnosis of suspected Lyme neuroborreliosis, and a control group comprising 42 patients with tick-borne encephalitis and 21 neurosurgical patients. The aim of the study was to analyze and compare findings of two PCR methods and
Borrelia burgdorferi
sensu lato culture results by examination of prospectively collected cerebrospinal fluid (CSF) and blood specimens from patients with clinical features of Lyme neuroborreliosis. Borrelial DNA was detected with at least one of the PCR approaches in 16/135 (11.9%) blood samples and 24/156 (15.4%) CSF samples. Using MseI restriction of PCR products of the amplified
rrf
-
rrl
region, we identified the majority of strains as
Borrelia afzelii
. Borreliae were isolated from 1/135 (0.7%) blood samples and from 5/156 (3.2%) CSF specimens. Using MluI restriction for characterization of isolated strains,
Borrelia garinii
was identified in all CSF isolates. Our study revealed that different approaches for direct demonstration of borrelial infection give distinct results, that there is an urgent need for standardization of the methods for direct detection of borrelial infection, and that the design of studies evaluating the validation of such methods should include appropriate control group(s) to enable assessment of both sensitivity and specificity.
Two-Year Study Evaluating the Potential Loss of Methicillin Resistance in a Methicillin-Resistant
Staphylococcus aureus
Culture Collection
Authors: Veguilla William , Peak K. Kealy , Luna Vicki A. , Roberts Jill C. , Davis Carisa R. , Cannons Andrew C. , Amuso Philip , Cattani Jacqueline
Published: August 2008

A reported loss of
mecA
prompted us to monitor 360 cryostocked methicillin-resistant
Staphylococcus aureus
strains for stability. Concurrently, 14 well-characterized strains were stored in a Microbank preservation system and subjected to multiple freeze-thaw events. There were no significant declines in the methicillin-resistant populations with either method over a two-year period.
Three-Dimensional Organization of Rift Valley Fever Virus Revealed by Cryoelectron Tomography
Authors: Freiberg Alexander N. , Sherman Michael B. , Morais Marc C. , Holbrook Michael R. , Watowich Stanley J.
Published: August 2008

Rift Valley fever virus (RVFV) is a member of the
Bunyaviridae
virus family (genus
Phlebovirus
) and is considered to be one of the most important pathogens in Africa, causing viral zoonoses in livestock and humans. Here, we report the characterization of the three-dimensional structural organization of RVFV vaccine strain MP-12 by cryoelectron tomography. Vitrified-hydrated virions were found to be spherical, with an average diameter of 100 nm. The virus glycoproteins formed cylindrical hollow spikes that clustered into distinct capsomeres. In contrast to previous assertions that RVFV is pleomorphic, the structure of RVFV MP-12 was found to be highly ordered. The three-dimensional map was resolved to a resolution of 6.1 nm, and capsomeres were observed to be arranged on the virus surface in an icosahedral lattice with clear T=12 quasisymmetry. All icosahedral symmetry axes were visible in self-rotation functions calculated using the Fourier transform of the RVFV MP-12 tomogram. To the best of our knowledge, a triangulation number of 12 had previously been reported only for Uukuniemi virus, a bunyavirus also within the
Phlebovirus
genus. The results presented in this study demonstrate that RVFV MP-12 possesses T=12 icosahedral symmetry and suggest that other members of the
Phlebovirus
genus, as well as of the
Bunyaviridae
family, may adopt icosahedral symmetry. Knowledge of the virus architecture may provide a structural template to develop vaccines and diagnostics, since no effective anti-RVFV treatments are available for human use.
Avian Influenza H6 Viruses Productively Infect and Cause Illness in Mice and Ferrets
Authors: Gillim-Ross Laura , Santos Celia , Chen Zhongying , Aspelund Amy , Yang Chin-Fen , Ye Dan , Jin Hong , Kemble George , Subbarao Kanta
Published: August 2008

Influenza pandemic preparedness has focused on influenza virus H5 and H7 subtypes. However, it is not possible to predict with certainty which subtype of avian influenza virus will cause the next pandemic, and it is prudent to include other avian influenza virus subtypes in pandemic preparedness efforts. An H6 influenza virus was identified as a potential progenitor of the H5N1 viruses that emerged in Hong Kong in 1997. This virus continues to circulate in the bird population in Asia, and other H6 viruses are prevalent in birds in North America and Asia. The high rate of reassortment observed in influenza viruses and the prevalence of H6 viruses in birds suggest that this subtype may pose a pandemic risk. Very little is known about the replicative capacity, immunogenicity, and correlates of protective immunity for low-pathogenicity H6 influenza viruses in mammals. We evaluated the antigenic and genetic relatedness of 14 H6 influenza viruses and their abilities to replicate and induce a cross-reactive immune response in two animal models: mice and ferrets. The different H6 viruses replicated to different levels in the respiratory tracts of mice and ferrets, causing varied degrees of morbidity and mortality in these two models. H6 virus infection induced similar patterns of neutralizing antibody responses in mice and ferrets; however, species-specific differences in the cross-reactivity of the antibody responses were observed. Overall, cross-reactivity of neutralizing antibodies in H6 virus-infected mice did not correlate well with protection against heterologous wild-type H6 viruses. However, we have identified an H6 virus that induces protective immunity against viruses in the North American and Eurasian lineages.
Vaccinia Virus Subverts a Mitochondrial Antiviral Signaling Protein-Dependent Innate Immune Response in Keratinocytes through Its Double-Stranded RNA Binding Protein, E3
Authors: Deng Liang , Dai Peihong , Parikh Tanvi , Cao Hua , Bhoj Vijay , Sun Qinmiao , Chen Zhijian , Merghoub Taha , Houghton Alan , Shuman Stewart
Published: August 2008

Skin keratinocytes provide a first line of defense against invading microorganisms in two ways: (i) by acting as a physical barrier to pathogen entry and (ii) by initiating a vigorous innate immune response upon sensing danger signals. How keratinocytes detect virus infections and generate antiviral immune responses is not well understood. Orthopoxviruses are dermatotropic DNA viruses that cause lethal disease in humans. Virulence in animal models depends on the virus-encoded bifunctional Z-DNA/double-stranded RNA (dsRNA)-binding protein E3. Here, we report that infection of mouse primary keratinocytes with a vaccinia ΔE3L mutant virus triggers the production of beta interferon (IFN-β), interleukin-6 (IL-6), CCL4, and CCL5. None of these immune mediators is produced by keratinocytes infected with wild-type vaccinia virus. The dsRNA-binding domain of E3 suffices to prevent activation of the innate immune response. ΔE3L induction of IFN-β, IL-6, CCL4, and CCL5 secretion requires mitochondrial antiviral signaling protein (MAVS; an adaptor for the cytoplasmic viral RNA sensors RIG-I and MDA5) and the transcription factor IRF3. IRF3 phosphorylation is induced in keratinocytes infected with ΔE3L, an event that depends on MAVS. The response of keratinocytes to ΔE3L is unaffected by genetic ablation of Toll-like receptor 3 (TLR3), TRIF, TLR9, and MyD88.
Characterization of a CRM1-Dependent Nuclear Export Signal in the C Terminus of Herpes Simplex Virus Type 1 Tegument Protein UL47
Authors: Williams Paul , Verhagen Janneke , Elliott Gillian
Published: August 2008

The herpes simplex virus type 1 tegument protein known as VP13/14, or hUL47, localizes to the nucleus and binds RNA. Using fluorescence loss in photobleaching analysis, we show that hUL47 undergoes nucleocytoplasmic shuttling during infection. We identify the hUL47 nuclear export signal (NES) as a C-terminal 10-residue hydrophobic peptide and measure its efficiency relative to that of the classical human immunodeficiency virus type 1 Rev NES. Finally, we show that the hUL47 NES is sensitive to the inhibitor of CRM1-mediated nuclear export leptomycin B. Hence, hUL47 joins a growing list of virus-encoded RNA-binding proteins that use CRM1 to exit the nucleus.
THE VARIETIES OF STEM RUST, PUCCINIA GRAMINIS PERS., OCCURRING ON BARBERRY IN EASTERN CANADA
Authors: Johnson T. , Green G. J.
Published: August 2008

In a study of 139 collections of aecia made on barberry in Eastern Canada during the period 1944–1949, it was found that variety Secalis of Puccinia graminis Pers. occurred in 103, var. Agrostidis in 55, var. Avenae in 33, var. Poae in 9, and var. Tritici in 8 collections. From the 33 isolates of var. Avenae, the following phy iologic races were determined (frequency of isolation in brackets): 1 (1), 2 (15), 5 (8), 6 (2), 7 (4), 8 (6), 10 (3), 11 (1), 12 (1). The eigh isolates of var. Tritici contained races 15 (3), 21 (1), 38 (1), 56 (1), 87 (1), 111 (1). Evidence from field surveys is in agreement with these results in that it indicates frequent spread of var. Secalis from barberry to susceptible grasses and of var, Avenae to oats.
THE REDUCTION OF FUSIFORM CAMBIAL CELLS IN CHAMAECYPARIS AND THUJA
Authors: Bannan M. W.
Published: August 2008

The loss of fusiform initials from the cambium, which is of frequent occurrence in all parts of the tree, takes place in different ways. Some cambial cells seem gradually to fail and are shortly lost from the cambium by maturation into more or less imperfect xylem or phloem elements. The majority are transversely subdivided by one or a succession of anticlinal divisions which begin near the center of the fusiform initial and usually extend to the daughter cells. The resulting segments shorten through the following periclinal divisions, some disappearing during the process of shortening and others undergoing transformation to ray initials. Nearly all new rays in the secondary body originate in this manner.
CARBOHYDRATE NUTRITION OFCHLORELLA VULGARIS
Authors: Neish A. C.
Published: August 2008

A substrain of the Pratt–Trelease strain of Chlorella vulgaris was grown at 30 °C. in light (200 ft-c.) and in darkness, on Emerson's medium enriched with various carbohydrates and related compounds in 1% concentration. D-glucose, D-fructose, D-galactose, and β-glucosides such as aesculin, cellobiose, lactose, and methyl-β-D-glucoside, are all good sources of carbon and energy for growth in darkness. Alpha glucosides such as sucrose, maltose, and methyl-α-D-glucoside are poor substrates as are also D-mannose, L-mannose, L-galactose, the pentoses, sugar acids, sugar alcohols, and polysaccharides. Illumination stimulates growth in the presence of D-glucose, D-fructose, and D-galactose more than in the presence of the β-glucosides. With methyl-β-D-glucoside better growth is obtained in darkness than in light. The optimum temperature for growth of the organism is near 35 °C. in the media used. Basal media containing nitrate nitrogen allow better utilization of sugars than those containing ammonia nitrogen. Most of the glucose utilized is converted to cellular material.
STUDIES ON CARBON AND NITROGEN SOUCES FOR THE PRODUCTION OF AMYLOLYTIC ENZYMES BY SUBMERGED CULTURE OF ASPERGILLUS NIGER
Authors: Shu P. , Blackwood A. C.
Published: August 2008

Aspergillus niger PRL 558 was used in the production of starch saccharifying enzymes. The culture was grown on 100 ml. of medium in 500 ml. Erlenmeyer flasks agitated and aerated on a rotary shaker at 35° C. Quantitative analyses for amylase, maltase, and limit dextrinase were determined on the culture filtrates. Variations in the specific type of carbohydrate source affected the yield of amylase markedly, and of maltase to a lesser extent. The production of limit dextrinase is the least dependent on the carbohydrate source. Maltose or compounds constituted of maltose units are essential for producing a maximum yield of amylase. The yields of the enzymes are related to the degree of the availability of the nitrogen source. Highest enzyme yields are obtained with hydrolyzed protein. However, the production of amylase and maltase is further stimulated by adding inorganic nitrogen compounds such as ammonium nitrate and sodium nitrate as a supplementary nitrogen source. The amounts of maltase and amylase obtained are controlled also by varying the fermentation time as well as the carbohudrate and protein content of the medium.
THE INTERMEDIATE METABOLISM OF PSEUDOMONAS AERUGINOSA: V.THE IDENTIFICATION OF PYRUVATE AS AN INTERMEDIATE IN GLUCOSE OXIDATION
Authors: Warburton Roger H. , Eagles B. A. , Campbell J. J. R.
Published: August 2008

Pyruvate has been determined at 16, 28, and 40 hr. in a culture of Pseudomonas aeruginosa when growing in a glucose medium. Throughout this interval the organism was shown to possess the enzyme system capable of rapidly oxidizing pyruvate. It was concluded that pyruvate is being formed and dissimilated continuously and that it is therefore to be considered an intermediate in the oxidation of glucose. It was found that glucose oxidation was not inhibited by 0.02 M fluoride and that pyruvate formation and utilization continued unimpaired in the presence of the inhibitor. This would indicate that enolase is not essential to the formation of pyruvate by P. aeruginosa and may be taken as further evidence supporting the contention that this organism does not dissimilate glucose by way of the conventional Embden–Meyerhof scheme.
NOTES ON THE CANADIAN TUCKAHOE, ITS OCCURRENCE IN CANADA AND THE INTERFERTILITY OF ITS PERFECT STAGE, POLYPORUS TUBERASTER JACQ. EX FRIES
Authors: Vanterpool T. C. , Macrae Ruth
Published: August 2008

The Canadian tuckahoe is the perennial sclerotium of Polyporus tuberaster jacq. ex Fries. It is commonly found in the parkland belt of the Canadian prairies where land supporting, virgin poplar groves, mainly Populus tremuloides Michx., is being brought under cultivation. Sporophore as many as three to a single sclerotium, appear in late June and July. Interfertility studies with single spore cultures isolated from sporophores derived from four sources in Western Canada and from one source in Italy have shown that both the Canadian fungus and the European P. tuberaster are heterothallic, have the tetrapolar type of interfertility, and are interfertile.
STUDIES IN THE BIOCHEMISTRY OF CELLULOLYTIC MICROORGANISMS: II.METABOLIC PRODUCTS OF POLYPORUS ABIETINUS, PENIOPHORA GIGANTEA, AND HYDNUM SEPTENTRIONALE
Authors: Whitaker D. R. , George Phyllis E.
Published: August 2008

The metabolic product causing a high "carbon unaccounted for" fraction in the carbon balance of Polyporus abietinus Dicks, ex Fr., was found to be D-mannitol. The metabolic product causing a high volatile neutral fraction in the carbon balances of Peniophora gigantea (Fr.) Massee and Hydnum septentrionale Fr, was found to be ethanol.
THE SOURCE OF RESISTANCE AND THE INHERITANCE OF REACTION TO 12 PHYSIOLOGIC RACES OF STEM RUST, PUCCINIA GRAMINIS AVENAE (ERIKSS. AND HENN.)
Authors: Welsh J. N. , Johnson T.
Published: August 2008

Resistance to 12 races of oat stem rust was unexpectedly obtained from three crosses, Hajira–Jostrain, Hajira–Richland, and Hajira–Banner, between the years 1932 and 1940. Recent investigations have shown that the Hajira parent was the source of this resistance, as 10% of plants selected from this variety were found to be highly resistant. Inheritance studies have shown that, in some crosses involving this source of resistance, two main genes are involved and in others only a single main gene. A probable explanation is that the highly resistant plants in Hajira may have differed genetically. The studies also reveal that the Hajira type of resistance to race 8, either in the seedling or adult stage, is indicative of resistance to the 12 races that occur in Canada and the United States.
AEROBIOLOGICAL SAMPLING METHODS FROM AIRCRAFT
Authors: Kelly C. D. , Pady S. M. , Polunin Nicholas
Published: August 2008

Three methods are described for sampling airborne bacteria and fungi from. aircraft. These methods were designed for use in aircraft flying at speeds about 200 m.p.h. The first is a qualitative method for use in a B-29 aircraft, with a sampling tube to hold a Petri dish 12 in. in front of the nose, yet permit loading and unloading from the interior. In the second and third methods, which are quantitative, the samplers are located inside the aircraft and air is brought to them by rubber hose connected to 1 in. aluminum elbows in a side window; the sampled air leaves the aircraft by another set of hose and elbows. The second sampling method uses a G.E. Electrostatic Bacterial Air Sampler located in an aluminum sampling chamber 18 in. × 18 in. × 18 in The third method utilizes filters made from glass wool and lens paper discs mounted in brass hose couplings. Numbers of organisms were calculated on a cubic foot basis from colonies which developed on nutrient media. In the second method, the organisms were precipitated directly on the agar surface; in the third method, however, the filters were shaken in sterile water and aliquot portions cultured in agar plates. For studying the numbers of fungous spores, silicone slides were substituted for agar in Petri plates exposed in the G.E. sampler. Typical results are given for the two quantitative methods.
TOBACCO ETCH VIRUS IN ONTARIO
Authors: Stover R. H.
Published: August 2008

Tobacco etch is one of the most widespread and injurious viruses on burley tobacco in Ontario. Three strains of this virus were obtained from tobacco collections. Their symptoms and behavior on tobacco and other hosts are described. Tobacco varieties were divided into two groups on the basis of their reaction to the etch virus. The group comprising all burley varieties tested showed severe symptoms while the other, comprising flue cured, dark, and cigar varieties, developed mild symptoms. The F1 from severe-symptom varieties × mild-symptom varieties exhibit mild symptoms while the F2 has segregated into severe- and mild-symptom types. The widespread occurrence of etch is attributed to the prevalence on tobacco of the vector Myzus persicae. A mixture of potato virus X (ringspot strain) and etch causes a more severe disease on burley tobacco than either virus by itself.
INHIBITION OF PLANT PATHOGENIC BACTERIA IN VITRO BY ANTIBIOTICS AND QUATERNARY AMMONIUM COMPOUNDS
Authors: Katznelson H. , Sutton M. D.
Published: August 2008

The bacteriostatic effect of certain antibiotics and quaternary ammonium compounds on representative genera and species of phytopathogenic bacteria has been studied. For Xanthomonas species aureomycin was the most potent agent with terramycin and polymyxin next; 0.1 to 0.05 p.p.m. aureomycin completely inhibited growth of most of the cultures at 24 hr. Terramycin was the most effective compound against Pseudomonas species followed by streptomycin and qureomycin; 0.2 to 0.1 p.p.m. terramycin inhibited growth of every culture tested with one exception. For Corynebacterium species aureomycin was most effective with neomycin and terramycin next, the activity of aureomycin varying from 0.4 to 0.05 p.p.m. Chloromycetin was the least effective of the antibiotics tested in the series of experiments. A comparision of the relative sensitivity of the three genera to a given antibiotic revealed that aureomycin and polymyxin were most effective on Xanithomonas, terramycin and streptomycin on Pseudomonas, and neomycin and chloromycetin on Corynecarotovora to polymyxin. the latter organism was generally more resistant to the antibiotics than the former. A number of other antibiotics and quaternaries: streptothricin, clavacin, gliotoxin, aspergillic acid, tyrothricin, penicillin, Roccal, Hyamine 1622, and compound L4-669 were also tested against strains of X. phaseoli and P> phaseolicola (agents of common and halo blight respectively of beans). None of these was as effective as aureomycin, polymyxin, streptomycin, or terramycin, the activity of the quaternaries being similar on the whole to that of chloromycetin.
STUDIES ON THE PRODUCTION OF VITAMIN B12-ACTIVE SUBSTANCES BY MICROORGANISMS
Authors: Burton Margaret O. , Lochhead A. G.
Published: August 2008

Vitamin B12activity, as determined by the Lactobacillus lactis Dorner agar plate assay, was shown by 64.6% of 537 bacteria isolated from soils, seed, manure, and poultry house litter, and by 66.6% of 676 actinomycetes from soils. For the primary isolation of active forms a simple medium without growth factors was superior to more complex media; however, the latter were more suitable for vitamin production. Further work, in which the Lactobacillus leichmannii assay method was used, indicated that highest yields were given by species of Nocardia isolated from soil, the B12-active substance being chiefly associated with the cells. Vitamin B12values could be increased by improving the method of extraction. Survivors of ultraviolet irradiation lethal to the great majority of treated cells were not significantly different in B12producing capacity with respect to mean or dispersion when compared with nonirradiated strains.