bluuebunny/crossref_metadata_2025 huggingface dataset:
Tight-binding theory of force constant models
Authors: van Schilfgaarde Mark , Sher Arden
Published: July 2002

A theory of force constant models is derived for tetrahedral semiconductors from Harrison’s [Phys. Rev. B 27, 3592 (1983)] tight-binding theory. A relation between the three independent elastic constants is derived that is independent of the detailed form of the matrix elements. This relation provides an approximate, but ab initio, theory on which two-parameter force constant models can be based. The universal matrix elements of Harrison are also found to describe remarkably well the magnitude of the elastic constants and their scaling from one material to another. Analytic forms for c11 and c44 are given in terms of the matrix elements.
Increase of effective viscosity of molten GaAs and InSb under an axial magnetic field
Authors: Ozawa Shoichi , Eguchi Minoru , Fujii Takashi , Fukuda Tsuguo
Published: July 2002

We have measured the effective dynamic viscosity of molten GaAs and InSb as a function of axial magnetic field by the oscillating vessel method. Effective viscosity of these semiconductor melts is observed to increase with the axial magnetic field intensity in the range of 0 to 5 kG.
Slip dislocation propagation in In-doped liquid encapsulated Czochralski GaAs during crystal growth
Authors: Ono Haruhiko , Kitano Tomohisa , Matsui Junji
Published: July 2002

A propagation rule was studied for two types of slip dislocations arising during crystal growth. In order to specify the dislocation distribution revealed by x-ray topography, we considered the relationship among the slip system, thermal gradient, and stress field. One type of slip dislocation was found to propagate on slip systems having a maximum Schmid factor in a uniform radial stress field, while another well known type occurred in a tangential stress field. It was concluded that different slip systems can be activated by specific stress fields caused by different thermal gradients under various growth conditions.
Lateral growth of GaAs over W by selective liquid phase epitaxy
Authors: Chung Ki-Woong , Kwon Young-Se
Published: July 2002

The GaAs/W/GaAs structures were made by selective liquid phase epitaxy which was simply explained by the diffusion-limited growth. The growth was independent of the direction of metal stripes. Using this method, a diode was fabricated and has shown good electrical characteristics.
Bipolar tunneling field-effect transistor: A three-terminal negative differential resistance device for high-speed applications
Authors: Leburton J. P. , Kolodzey J. , Briggs S.
Published: July 2002

Carrier injection across a tunnel homojunction is suggested as a new mechanism for a high-speed three-terminal device. The novel feature is the two-dimensional homojunction tunneling within a bipolar modulation doping structure. Negative differential resistance characterized by large peak-to-valley current ratios and high transconductance is anticipated. Estimates of the relevant time constants of the tunnel structure suggest the possibility of very high frequency operation.
High-temperature stability of Nb/GaAs and NbN/GaAs interfaces
Authors: Ding J. , Lee B. , Gronsky R. , Washburn J. , Chin D. , Van Duzer T.
Published: July 2002

The interface stabilities of Nb/GaAs and NbN/GaAs contacts at temperatures up to 700 °C for Nb/GaAs and 850 °C for NbN/GaAs have been investigated by transmission electron microscopy and x-ray diffractometry techniques. Results reveal that a Nb/GaAs reaction takes place at temperatures above 600 °C, and interdiffusion at the NbN/GaAs interface occurs at temperatures above 800 °C. The correlation between the observed interface morphologies before and after annealing and previously reported electrical properties of these contacts is also discussed.
Widely tunable active Bragg reflector integrated lasers in InGaAsP-InP
Authors: Broberg Björn , Nilsson Stefan
Published: July 2002

Monolithic InGaAsP-InP lasers comprising an active Bragg reflector integrated with a separately pumped wide-band gain region have been developed. The lasers operate in a dynamic single mode in the 1.55 μm wavelength region. By adjusting the current through the Bragg reflector, the wavelength can be tuned. The maximum tuning range is 11.6 nm.
Measurement of the valence-band discontinuities for molecular organic semiconductor/inorganic semiconductor heterojunctions
Authors: So F. F. , Forrest S. R.
Published: July 2002

Using the temperature dependence of the forward-biased current-voltage characteristics as well as internal photoemission, we directly measure the barrier potential and valence-band discontinuity energy (ΔEv ) of isotype heterojunctions formed between thin films of the crystalline organic semiconductor: 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) and p-Si. We find ΔEv =(0.50±0.02) eV. This, to our knowledge, is the first report of a measurement of a band discontinuity energy between a crystalline organic semiconductor and an inorganic semiconductor. These results are consistent with predictions of a current model involving diffusion and drift in the organic-on-inorganic (OI) semiconductor device. This model is employed to calculate ΔEv using previously obtained barrier energies for several different PTCDA/inorganic semiconductor devices. In all cases, values of the barrier diffusion potential and ΔEv are considerably smaller than apparent barrier energies obtained previously using pure thermionic emission theory to explain transport of charge over the OI barrier.
Laser desorption of polymer in a plasma reactor
Authors: Holber W. , Gaines D. , Yu C. F. , Osgood R. M.
Published: July 2002

Low-power ultraviolet (350 nm) laser light has been used to inhibit polymer formation on silicon in a plasma reactor containing CF4 /H2 reactants. The resultant increase in etch rate has been studied as a function of hydrogen partial pressure. Auger electron spectroscopy reveals a reduction in polymer formation in the area illuminated by the laser.
Wear reduction of glassy carbon by Li implantation
Authors: Yoshida Kazuo , Takahashi Katsuo , Okuno Kazuhiko , Katagiri Gen , Iwaki Masaya , Ishitani Akira
Published: July 2002

A study has been made of the effect of Li implantation on wear properties of glassy carbon (GC). Abrasive wear tests with a silicon carbide abrasive paper showed that Li implantation greatly reduced the wear volume of GC. Raman spectroscopy indicated that Li implantation changes the surface structure from disordered graphite to amorphous. Depth profiles of Li measured by secondary ion mass spectroscopy showed the migration of Li atoms towards the surface. It is concluded that the reduction of wear volume due to Li implantation may be caused by the formation of amorphous structure and/or the surface enrichment of implanted Li atoms.
Hall effect in amorphous Si:H and amorphous Si:H/amorphous Ge:H superlattices
Authors: Sichel E. K. , Greber L. , Wang K.
Published: July 2002

The sign anomaly in the Hall coefficient observed in substitutionally doped amorphous Si:H and amorphous Ge:H is also found in amorphous Si:H/Ge:H superlattices. The size of the Hall mobility in the superlattice is comparable to the Hall mobility in amorphous Si:H and amorphous Ge:H.
Extremely high negative photoconductivity in p-modulation-doped GaAs quantum wells
Authors: Höpfel R. A.
Published: July 2002

In p-modulation-doped quantum wells of GaAs/AlGaAs extremely high negative photoconductivity is observed at low temperatures. The in-plane sheet resistance can be increased by a factor of more than 60 with illumination of less than 1 W/cm2. Spectral analysis shows that the effect is mainly due to hole trapping in the potential minima of AlGaAs and subsequent recombination of minority electrons.
High quality silicon-on-insulator structure formed by oxygen implantation and lamp annealing
Authors: Vu D. P. , Haond M. , d’Anterroches C. , Oberlin J. C. , Golanski A. , Grob J. J. , Maillet S.
Published: July 2002

A silicon-on-insulator (SOI) structure was formed by implanting 150 keV O+ ions into a single-crystal n-type Si. The substrate temperature during implantation was maintained at 600 °C. Implanted samples were subsequently annealed in the ambient air at 1350 °C for 70 min using a halogen lamp oven and analyzed using the Rutherford backscattering/channeling technique, cross-sectional electron microscopy, and high-resolution electron microscopy. It is shown that the resulting dislocation density within the top Si layer (105–106/cm2) is two to three orders of magnitude lower than the dislocation density previously reported for the SOI structures implanted under similar conditions and subsequently annealed in an inert gas ambient or under vacuum.
High rate synthesis of diamond by dc plasma jet chemical vapor deposition
Authors: Kurihara Kazuaki , Sasaki Kenichi , Kawarada Motonobu , Koshino Nagaaki
Published: July 2002

This letter describes the first successful attempt at synthesizing diamond by chemical vapor deposition with the use of a dc plasma jet. A plasma jet, formed by the dc arc discharge of CH4 diluted with H2, was sprayed onto a water-cooled substrate. The growth rate of the diamond film was 80 μm/h. The crystallinity measures well in terms of x-ray diffraction and Raman spectroscopy. The quenching effect of the thermal plasma is discussed in relation to the high growth rate obtained.
Effects of fluorine ion implantation on metal-oxide-semiconductor devices of silicon-on-sapphire
Authors: Zaima Shigeaki , Yasuda Yukio , Ito Masahiro , Nakamura Tetsuro
Published: July 2002

Effects of fluorine ion implantation on electrical characteristics of metal-oxide-semiconductor (MOS) devices on silicon-on-sapphire have been investigated. The fluorine implantation generates deep acceptor levels, the nature of which is significantly affected by the sequence of the implantation and gate oxidation in device fabrication process steps. It was found that drain leakage current of fluorine-implanted MOS transistors can be reduced to about 0.1 times compared with unimplanted devices without degrading the basic electrical characteristics.
Organometallic epitaxy of HgCdTe on CdTeSe substrates with high compositional uniformity
Authors: Ghandhi Sorab K. , Bhat Ishwara B. , Fardi Hamid
Published: July 2002

We report here on the growth of Hg0.8Cd0.2Te on lattice-matched substrates of CdTe0.96Se0.04 by organometallic vapor phase epitaxy. Results are compared with those for comparable layers grown on CdTe substrates. It is shown that the use of lattice-matched substrates results in active layers of improved structural quality, as evidenced by the results of double-crystal x-ray diffraction measurements. A compositional uniformity of better than ±0.005 (in the Cd composition) was obtained over 1 cm ×2 cm area substrates, corresponding to a standard deviation of 0.0024. The thickness uniformity was better than ±0.7 μm for 12-μm-thick layers. These layers were deposited by the direct alloy growth, without the interdiffusion of separate layers of HgTe and CdTe. Both n- and p-type layers have been grown by suitable modification to the growth process. Mobility values in excess of 6×105 cm2/V s were obtained in n-type material (x=0.2), with an electron concentration below 1×1015 cm−3. With p-type layers, mobility values of 400 cm2/V s were obtained with a hole concentration of 1×1017 cm−3.
Influence of rapid thermal annealing temperature on the electrical properties of Be-implanted GaAs p-n junctions
Authors: de Lyon T. J. , Casey H. C. , Massoud H. Z. , Timmons M. L. , Hutchby J. A. , Dietrich H. B.
Published: July 2002

Planar, Be-implanted p-n junctions were fabricated in GaAs with rapid thermal annealing (RTA). Five second isochronal anneals over a temperature range of 600–1000 °C were studied with secondary ion mass spectrometry (SIMS), sheet resistance measurements, and variable diameter p-n junctions. Sheet resistance measurements indicate that a minimum RTA temperature of 600 °C is necessary for electrical activation of the implanted Be. SIMS analysis indicates that significant outdiffusion and surface evaporation of Be occur at all RTA temperatures in this range, while indiffusion of Be is insignificant for concentrations below 1×1018 cm−3. Forward bias current in diodes ranging in diameter from 10 to 1000 μm is dominated by surface recombination, rather than bulk space-charge recombination, over the entire 600–1000 °C temperature range. The magnitude of the surface recombination current is insensitive to the RTA temperature, which suggests that 600 °C RTA should be sufficient for the formation of satisfactory p-n junctions.
Comment on ‘‘Low-frequency excess noise in Nb-Al2O3-Nb Josephson tunnel junctions’’ [Appl. Phys. Lett. 5
0, 1757 (1987)]
Authors: Kleinpenning T. G. M.
Published: July 2002

The 1/f noise in a josephson junction as measured by Savo et al. can b terpreted in terms of transparency fluctuations induced by Nyquist noise i n th aluminium oxide layer. (AIP)
Response to ‘‘Comment on ‘Low-frequency excess noise in Nb-Al2O3-Nb Josephson tunnel junctions’ ’’ [Appl. Phys. Lett. 5
2, 2001 (1988)]
Authors: Savo Bonaventura , Wellstood Frederick C. , Clarke John
Published: July 2002

A new theory is needed to explain the low−frequency 1/f noise in niobi aluminium oxide−niobium Josephson tunnel junctions. (AIP)
Optically controlled GaAs/AlAs multiple quantum well modulators employing integrated dielectric reflectors
Authors: Kowalsky W. , Hackbarth Th. , Ebeling K. J.
Published: July 2002

We investigate all-optical switching in GaAs/AlAs multiple quantum well devices with integrated dielectric reflector. A 7 mW control beam at λc=790 nm wavelength produces a 15% reflection change for a test beam at λt=858 nm which is close to the lowest energy transition in the quantum wells (λ=868 nm). Switching dynamics are shown to be limited by excess carrier lifetimes of τ≊4 ns corresponding to a 3 dB frequency of 70 MHz. A basic analysis in terms of carrier-induced absorption change by dynamic band filling provides a good description of the experiments.
AlGaAs doping superlattices grown by molecular beam epitaxy
Authors: Ackley D. E. , Lee H. , Nouri N. , Colvard C.
Published: July 2002

AlGaAs doping superlattices (‘‘nipi structures’’) have been successfully grown in 30% AlGaAs by molecular beam epitaxy. Tunable photoluminescence (PL) as a function of incident laser intensity has been observed in samples with a wide range of intrinsic layer thicknesses over a temperature range from 2 to 120 K. Luminescence shifts as large as 230 meV were observed for a range of incident intensities of about 500. Low-temperature PL spectra showed a weaker dependence of the peak energy on incident intensity for thicker spacer layers. This decrease in tuning rate can be associated with the reduced probability for tunneling transitions with increasing spacer thickness.
Characteristics of a monolithically integrated doping superlattice optical circuit
Authors: Hasnain G. , Chang-Hasnain C. , Dienes A. , Whinnery J. R.
Published: July 2002

Characteristics of a monolithically integrated optical circuit made of GaAs doping superlattices are investigated. Qualitative explanations of the results are given. The results show that doping superlattices have potential for integrated optics applications.
Field-induced anisotropic conductivity in the granular superconducting ceramic oxide YBa2Cu3O7−y
Authors: Laurent Ch. , Vanderschueren H. W. , Tarte P. , Rulmont A. , Ausloos M.
Published: July 2002

A novel experimental procedure has been achieved in order to study the anisotropy properties of the new superconducting oxide ceramics. A magnetic field induced anisotropy confirms the drastic role of the orientation of the crystallites on the knee appearance when cooling the granular Y1Ba2Cu3O7−y superconductor below the ‘‘critical temperature’’ Tc. The results are explained through the preferential destruction of two-dimensional supercurrent paths due to the upper critical field anisotropy.
Time delay of stimulated Raman scattering of micron-size droplets
Authors: Chýlek Petr , Biswas A. , Jarzembski M. A. , Srivastava V. , Pinnick R. G.
Published: July 2002

We have observed time delay of several nanoseconds of the stimulated Raman scattering from 80-μm-diam CCl4 droplets. The same time delay is observed in the laser-induced breakdown of the droplets. No time delay is observed for the stimulated Raman scattering and the laser-induced breakdown of the bulk liquid CCl4. We suggest that the observed time delay is related to the time required to build up a strong field enhancement inside micron-size droplets.
Measurement of high-order optical nonlinear susceptibilities in semiconductor-doped glasses
Authors: Acioli L. H. , Gomes A. S. L. , Leite J. R. Rios
Published: July 2002

The optical susceptibilities of CdSxSe1−x -doped glasses were observed up to χ(11) using a spatially resolved phase-matched multiwave mixing technique. Using a pulsed dye laser tuned near the band gap, measurements were performed for ‖χ(3)‖, ‖χ(5)‖, and ‖χ(7)‖ in four different commercial filter glasses.
Optoelectronic transient response of the self-aligned double-heterostructure optoelectronic switch
Authors: Crawford D. L. , Taylor G. W. , Cooke P. , Chang T. Y. , Tell B. , Simmons J. G.
Published: July 2002

Fabrication and characterization of a three-terminal self-aligned double-heterostructure optoelectronic switch in the light-emitting diode configuration are reported. Results demonstrating device switching characteristics are presented, in which switching is triggered by electrical or optical stimuli. Electrical switch-on and switch-off transitions occur in 10 ns, under electrical stimulus. Corresponding optical turn-on times of 60 ns are observed. With an optical switching energy of 0.02 fJ/μm2, an electrical switch-on transition of 4 ns is observed.
Contact regrowth technique for low-resistance nonalloyed contacts to the hot-electron transistor
Authors: Peng C. K. , Chen J. , Morkoç H.
Published: July 2002

We report a novel contact regrowth technique for the formation of extremely low nonalloyed ohmic contacts. The successful demonstration of this technique is reported on an InGaAs/InAlAs hot-electron transistor device. For the investigated InGaAs-based structure, the regrown contacting scheme reported includes an In0.53Ga0.47As layer, in InAs/GaAs strained-layer superlattice, and an InAs cap, all heavily doped n type with Si. A very low specific contact resistance of 1.8×10−7 Ω cm2 to the base layer is obtained. The higher current densities achieved in the transistor characteristics are in close agreement with calculations, and a contact model is presented explaining the poor results of conventional nonalloyed contacts.
Optical fiber spatial filtering technique for investigating carrier dynamics
Authors: Tai K. , McCall S. L. , Tsang W. T.
Published: July 2002

A new technique using single-mode fibers as spatial filters for probing carrier dynamics such as diffusion and recombination is introduced. Diffusion coefficients of 5.5 and 5 cm2/s are obtained for optically excited electron-hole plasmas in a 1.9-μm-thick In0.6Ga0.4As0.85P0.15 bulk layer and in an In0.53Ga0.47As/InP quantum well sample with well thickness of 100 Å, respectively.
Transmission optical device to produce intense polarized neutron beams
Authors: Mook H. A. , Hayter John B.
Published: July 2002

It is shown how a device can be constructed using a stack of magnetic supermirrors to produce high-intensity polarized neutron beams with a large area. The device makes use of the fact that single-crystal Si is transparent to neutrons. A prototypical device has been constructed which provides 64% neutron efficiency with 20 min collimation.
Antiferromagnetic spin waves in superlattices of diluted magnetic semiconductors
Authors: Villeret Murielle , Rodriguez S. , Kartheuser E.
Published: July 2002

We present an analysis of the long-wavelength spin-wave excitations in superlattices of diluted magnetic semiconductors. The different magnetic modes are classified as ‘‘pure-bulk,’’ ‘‘pure-interface,’’ and ‘‘bulk-interface’’ depending on whether they propagate along the axis of the superlattice in the two components of the structure, they decay in both regions, or they propagate in one and decay in the other. Numerical applications are considered related to inelastic light scattering from superlattices of Cd1−xMnxTe.
Low-frequency resonant Raman scattering in AlAs-GaAs atomic-layer superlattices
Authors: Toriyama Takeshi , Kobayashi Naoki , Horikoshi Yoshiji
Published: July 2002

New Raman lines are observed at the lowest ever frequencies in (AlAs)1(GaAs)n (n=1,2,3) atomic-layer superlattices under band-gap resonant excitation at low temperature. These lines appear in the 30–60 cm−1 region and their intensity is resonantly enhanced as the excitation photon energy approaches the photoluminescence peak energy. Analyses using the elastic continuum model indicate that these lines could be attributed to folded transverse acoustic phonons near the Brillouin-zone edge of the superlattices.
Low-frequency acoustic anomalies in lithium niobate Mach–Zehnder interferometers
Authors: Jungerman R. L. , Flory C. A.
Published: July 2002

Anomalous variation in the frequency response of z-cut and x-cut Mach–Zehnder traveling-wave optical modulators near 50 MHz has been observed. Measurements of loss in the coplanar electrode and coupling to an adjacent acoustic transducer indicate the effect is due to surface acoustic waves in the device. Application of an acoustic absorber reduces the frequency response variation.
Molecules, muscles, and machines: Universal performance characteristics of motors
Authors: Marden James H. , Allen Lee R.
Published: July 2002

Animal- and human-made motors vary widely in size and shape, are constructed of vastly different materials, use different mechanisms, and produce an enormous range of mass-specific power. Despite these differences, there is remarkable consistency in the maximum net force produced by broad classes of animal- and human-made motors. Motors that use force production to accomplish steady translational motion of a load (myosin, kinesin, dynein, and RNA polymerase molecules, muscle cells, whole muscles, winches, linear actuators, and rockets) have maximal force outputs that scale as the two-thirds power of mass, i.e., with cross-sectional area. Motors that use cyclical motion to generate force and are more subject to multiaxial stress and vibration have maximal force outputs that scale as a single isometric function of motor mass with mass-specific net force output averaging 57 N⋅kg
−1
(SD = 14). Examples of this class of motors includes flying birds, bats, and insects, swimming fish, various taxa of running animals, piston engines, electric motors, and all types of jets. Dependence of force production and stress resistance on cross-sectional area is well known, but the isometric scaling and common upper limit of mass-specific force production by cyclical motion motors has not been recognized previously and is not explained by an existing body of theory. Remarkably, this finding indicates that most of the motors used by humans and animals for transportation have a common upper limit of mass-specific net force output that is independent of materials and mechanisms.
Genetically altered AMPA-type glutamate receptor kinetics in interneurons disrupt long-range synchrony of gamma oscillation
Authors: Fuchs Elke C. , Doheny Helen , Faulkner Howard , Caputi Antonio , Traub Roger D. , Bibbig Andrea , Kopell Nancy , Whittington Miles A. , Monyer Hannah
Published: July 2002

Gamma oscillations synchronized between distant neuronal
populations may be critical for binding together brain regions devoted
to common processing tasks. Network modeling predicts that such
synchrony depends in part on the fast time course of excitatory
postsynaptic potentials (EPSPs) in interneurons, and that even moderate
slowing of this time course will disrupt synchrony. We generated mice
with slowed interneuron EPSPs by gene targeting, in which the gene
encoding the 67-kDa form of glutamic acid decarboxylase (GAD67) was
altered to drive expression of the
α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) glutamate
receptor subunit GluR-B. GluR-B is a determinant of the relatively slow
EPSPs in excitatory neurons and is normally expressed at low levels in
γ-aminobutyric acid (GABA)ergic interneurons, but at high levels in
the GAD-GluR-B mice. In both wild-type and GAD-GluR-B mice, tetanic
stimuli evoked gamma oscillations that were indistinguishable in local
field potential recordings. Remarkably, however, oscillation synchrony
between spatially separated sites was severely disrupted in the mutant,
in association with changes in interneuron firing patterns. The
congruence between mouse and model suggests that the rapid time course
of AMPA receptor-mediated EPSPs in interneurons might serve to allow
gamma oscillations to synchronize over distance.
Notch receptor cleavage depends on but is not directly executed by presenilins
Authors: Taniguchi Yoshihito , Karlström Helena , Lundkvist Johan , Mizutani Tomohiko , Otaka Akira , Vestling Monica , Bernstein Alan , Donoviel Dorit , Lendahl Urban , Honjo Tasuku
Published: July 2002

Notch receptors undergo three distinct proteolytic cleavages during maturation and activation. The third cleavage occurs within the plasma membrane and results in the release and translocation of the intracellular domain into the nucleus to execute Notch signaling. This so-called γ-secretase cleavage is under the control of presenilins, but it is not known whether presenilins themselves carry out the cleavage or whether they act by means of yet-unidentified γ-secretase(s). In this article, we show that Notch intracellular cleavage in intact cells completely depends on presenilins. In contrast, partial purification of the Notch cleavage activity reveals an activity, which is present only in protein extracts from presenilin-containing cells, and which does not comigrate with presenilin. This finding provides evidence for the existence of a specific Notch-processing activity, which is physically distinct from presenilins. We conclude from these experiments that presenilins are critically required for Notch intracellular cleavage but are not themselves directly mediating the cleavage.
Noninvasive quantitative imaging of protein–protein interactions in living subjects
Authors: Ray P. , Pimenta H. , Paulmurugan R. , Berger F. , Phelps M. E. , Iyer M. , Gambhir S. S.
Published: July 2002

We are developing methods to image molecular and cellular events in living subjects. In this study, we validate imaging of protein—protein interactions in living mice by using bioluminescent optical imaging. We use the well studied yeast two-hybrid system adapted for mammalian cells and modify it to be inducible. We employ the NF-κB promoter to drive expression of two fusion proteins (VP16-MyoD and GAL4-ID). We modulate the NF-κB promoter through tumor necrosis factor α. Firefly luciferase reporter gene expression is driven by the interaction of MyoD and ID through a transcriptional activation strategy. We demonstrate the ability to detect this induced protein–protein interaction in cell culture and image this induced interaction in living mice by using transiently transfected cells. The current approach will be a valuable and potentially generalizable tool to noninvasively and quantitatively image protein–protein interactions in living subjects. The approaches validated should have important implications for the study of protein–protein interactions in cells maintained in their natural
in vivo
environment as well as for the
in vivo
evaluation of new pharmaceuticals targeted to modulate protein–protein interactions.
Behavior of several two-dimensional fluid equations in singular scenarios
Authors: Cordoba Diego , Fefferman Charles
Published: July 2002

We give conditions that rule out formation of sharp fronts for certain two-dimensional incompressible flows. We show that a necessary condition of having a sharp front is that the flow has to have uncontrolled velocity growth. In the case of the quasi-geostrophic equation and two-dimensional Euler equation, we obtain estimates on the formation of semi-uniform fronts.
HLTF gene silencing in human colon cancer
Authors: Moinova Helen R. , Chen Wei-Dong , Shen Lanlan , Smiraglia Dominic , Olechnowicz Joseph , Ravi Lakshmeswari , Kasturi Lakshmi , Myeroff Lois , Plass Christoph , Parsons Ramon , Minna John , Willson James K. V. , Green Sylvan B. , Issa Jean-Pierre , Markowitz Sanford D.
Published: July 2002

Chromatin remodeling enzymes are increasingly implicated in a variety of important cellular functions. Various components of chromatin remodeling complexes, including several members of the SWI/SNF family, have been shown to be disrupted in cancer. In this study we identified as a target for gene inactivation in colon cancer the gene for helicase-like transcription factor (
HLTF
), a SWI/SNF family protein. Loss of HLTF expression accompanied by
HLTF
promoter methylation was noted in nine of 34 colon cancer cell lines. In these cell lines HLTF expression was restored by treatment with the demethylating agent 5-azacytidine. In further studies of primary colon cancer tissues,
HLTF
methylation was detected in 27 of 63 cases (43%). No methylation of
HLTF
was detected in breast or lung cancers, suggesting selection for
HLTF
methylation in colonic malignancies. Transfection of HLTF suppressed 75% of colony growth in each of three different HLTF-deficient cell lines, but showed no suppressive effect in any of three HLTF-proficient cell lines. These findings show that HLTF is a common target for methylation and epigenetic gene silencing in colon cancer and suggest
HLTF
is a candidate colon cancer suppressor gene.
Removal of oxygen free-radical-induced 5′,8-purine cyclodeoxynucleosides from DNA by the nucleotide excision-repair pathway in human cells
Authors: Kuraoka Isao , Bender Christina , Romieu Anthony , Cadet Jean , Wood Richard D. , Lindahl Tomas
Published: July 2002

Exposure of cellular DNA to reactive oxygen species generates several classes of base lesions, many of which are removed by the base excision-repair pathway. However, the lesions include purine cyclodeoxynucleoside formation by intramolecular crosslinking between the C-8 position of adenine or guanine and the 5′ position of 2-deoxyribose. This distorting form of DNA damage, in which the purine is attached by two covalent bonds to the sugar-phosphate backbone, occurs as distinct diastereoisomers. It was observed here that both diastereoisomers block primer extension by mammalian and microbial replicative DNA polymerases, using DNA with a site-specific purine cyclodeoxynucleoside residue as template, and consequently appear to be cytotoxic lesions. Plasmid DNA containing either the 5′
R
or 5′
S
form of 5′,8-cyclo-2-deoxyadenosine was a substrate for the human nucleotide excision-repair enzyme complex. The
R
diastereoisomer was more efficiently repaired than the
S
isomer. No correction of the lesion by direct damage reversal or base excision repair was detected. Dual incision around the lesion depended on the core nucleotide excision-repair protein XPA. In contrast to several other types of oxidative DNA damage, purine cyclodeoxynucleosides are chemically stable and would be expected to accumulate at a slow rate over many years in the DNA of nonregenerating cells from xeroderma pigmentosum patients. High levels of this form of DNA damage might explain the progressive neurodegeneration seen in XPA individuals.
A universal scaling law between gray matter and white matter of cerebral cortex
Authors: Zhang Kechen , Sejnowski Terrence J.
Published: July 2002

Neocortex, a new and rapidly evolving brain structure in mammals, has a similar layered architecture in species over a wide range of brain sizes. Larger brains require longer fibers to communicate between distant cortical areas; the volume of the white matter that contains long axons increases disproportionally faster than the volume of the gray matter that contains cell bodies, dendrites, and axons for local information processing, according to a power law. The theoretical analysis presented here shows how this remarkable anatomical regularity might arise naturally as a consequence of the local uniformity of the cortex and the requirement for compact arrangement of long axonal fibers. The predicted power law with an exponent of 4/3 minus a small correction for the thickness of the cortex accurately accounts for empirical data spanning several orders of magnitude in brain sizes for various mammalian species, including human and nonhuman primates.
Genetic alterations of IL-1 receptor antagonist in mice affect plasma cholesterol level and foam cell lesion size
Authors: Devlin Cecilia M. , Kuriakose George , Hirsch Emmet , Tabas Ira
Published: July 2002

Inflammatory cytokines have been linked to atherosclerosis by using cell culture models and acute inflammation in animals. The goal of this study was to examine lipoprotein levels and early atherosclerosis in chronic animal models of altered IL-1 physiology by using mice with deficient or excess IL-1 receptor antagonist (IL-1ra). IL-1ra knockout C57BL/6J mice fed a cholesterol/cholate diet for 3 mo had a 3-fold decrease in non-high-density lipoprotein cholesterol and a trend toward increased foam-cell lesion area compared to wild-type littermate controls. IL-1ra transgenic/low-density lipoprotein receptor (LDLR) knockout mice fed a cholesterol-saturated fat diet for 10 wk showed a 40% increase in non-high-density lipoprotein cholesterol, consistent with the IL-1ra knockout data, although there was no change in lesion size. When these IL1-ra overexpressing transgenic mice on the LDLR knockout background were fed a high-cholesterol/high-fat diet containing cholate, however, a statistically significant 40% decrease in lesion area was observed compared to LDLR knockout mice lacking the transgene. By immunohistochemistry, IL-1ra was present in C57BL/6J and LDLR knockout aortae, absent in IL-1ra knockout aortae, and present at high levels in LDLR knockout/IL-1ra transgene aortae. In summary, IL-1ra tended to increase plasma lipoprotein levels and, when fed a cholate-containing diet, decrease foam-cell lesion size. These data demonstrate that in selected models of murine atherosclerosis, chronic IL-1ra depletion or overexpression has potentially important effects on lipoprotein metabolism and foam-cell lesion development.
Exploring the sequence space for tetracycline-dependent transcriptional activators: Novel mutations yield expanded range and sensitivity
Authors: Urlinger Stefanie , Baron Udo , Thellmann Marion , Hasan Mazahir T. , Bujard Hermann , Hillen Wolfgang
Published: July 2002

Regulatory elements that control tetracycline resistance in
Escherichia coli
were previously converted into highly specific transcription regulation systems that function in a wide variety of eukaryotic cells. One tetracycline repressor (TetR) mutant gave rise to rtTA, a tetracycline-controlled transactivator that requires doxycycline (Dox) for binding to
tet
operators and thus for the activation of P
tet
promoters. Despite the intriguing properties of rtTA, its use was limited, particularly in transgenic animals, because of its relatively inefficient inducibility by doxycycline in some organs, its instability, and its residual affinity to
tetO
in absence of Dox, leading to elevated background activities of the target promoter. To remove these limitations, we have mutagenized tTA DNA and selected in
Saccharomyces cerevisiae
for rtTA mutants with reduced basal activity and increased Dox sensitivity. Five new rtTAs were identified, of which two have greatly improved properties. The most promising new transactivator, rtTA2
S
-M2, functions at a 10-fold lower Dox concentration than rtTA, is more stable in eukaryotic cells, and causes no background expression in the absence of Dox. The coding sequences of the new reverse TetR mutants fused to minimal activation domains were optimized for expression in human cells and synthesized. The resulting transactivators allow stringent regulation of target genes over a range of 4 to 5 orders of magnitude in stably transfected HeLa cells. These rtTA versions combine tightness of expression control with a broad regulatory range, as previously shown for the widely applied tTA.
TRAF6
-deficient mice display hypohidrotic ectodermal dysplasia
Authors: Naito Asuka , Yoshida Hisahiro , Nishioka Eri , Satoh Mizuho , Azuma Sakura , Yamamoto Tadashi , Nishikawa Shin-ichi , Inoue Jun-ichiro
Published: July 2002

Tumor necrosis factor receptor (TNFR)-associated factor 6 (TRAF6) is an adapter protein that links signals from members of the TNFR superfamily and Toll/IL-1 receptor family to activation of transcription factors NFκB and AP-1. Analysis of
TRAF6
-deficient mice revealed that TRAF6 is essential for normal bone formation and establishment of immune and inflammatory systems. Here we report that
TRAF6
deficiency results in defective development of epidermal appendixes, including guard hair follicles, sweat glands, sebaceous glands of back skin, and modified sebaceous glands such as meibomian glands, anal glands, and preputial glands. Except the sebaceous gland impairment, these abnormal phenotypes are identical to those observed in
Tabby
(
Ta
),
downless
(
dl
), and
crinkled
(
cr
) mice, which are models of hypohidrotic (anhidrotic) ectodermal dysplasia in human. β-catenin and mucosal addressin cell adhesion molecule-1, an early marker of developing guard-hair follicles is absent in the skin of
TRAF6
-deficient embryos. Thus, TRAF6 is essential for development of epidermal appendixes. TRAF6 does not associate with the cytoplasmic tail of the
dl
protein (DL)/ectodysplasin receptor (EDAR) receptor, which, when mutated, results in hypohidrotic (anhidrotic) ectodermal dysplasia. However, TRAF6 associates with X-linked ectodysplasin-A2 receptor (XEDAR) and TNFR super family expressed on the mouse embryo (TROY/toxicity and JNK inducer (TAJ), which are EDAR-related members of the TNFR superfamily that are expressed at high level in epidermal appendixes. Furthermore, TRAF6 is essential for the XEDAR-mediated NFκB activation. Our results suggest that TRAF6 may transduce signals emanating from XEDAR or TROY/TAJ that are associated with development of epidermal appendixes.
Orbitofrontal cortex: A key prefrontal region for encoding information
Authors: Frey Stephen , Petrides Michael
Published: July 2002

Little is known about the specific functional contribution of the human orbitofrontal cortex with regard to memory processing, although there is strong evidence from lesion studies in monkeys that it may play an important role. The present investigation measured changes in regional cerebral blood flow with positron emission tomography in normal human subjects who were instructed to commit to memory abstract visual patterns. The results indicated that the rostral orbitofrontal region (area 11), which is primarily linked with the anterior medial temporal limbic region and lateral prefrontal cortical areas, is involved in the process of encoding of new information.
Molecular cloning of Porimin, a novel cell surface receptor mediating oncotic cell death
Authors: Ma Fengrong , Zhang Chonghui , Prasad K. V. S. , Freeman Gordon J. , Schlossman Stuart F.
Published: July 2002

Anti-Porimin (Pro-oncosisreceptorinducingmembraneinjury) mAb mediates oncosis-like cell death in Jurkat cells. Porimin cDNA was isolated from a Jurkat cell cDNA library by COS cell-expression cloning. The 3,337-bp cDNA has an ORF of 567 bp, encoding a type I transmembrane protein of 189 amino acids. The extracellular domain of Porimin contains manyO-linked and sevenN-linked glycosylation sites that define it as a new member of the mucin family. COS7 and 293 cells transiently transfected with Porimin cDNA were specifically recognized by anti-Porimin Ab in cell staining and immunoblotting experiments. When expressed in Jurkat cells, a His-tagged Porimin cDNA construct resulted in the generation of a specific 110-kDa-size protein that matched the molecular mass of the endogenous Porimin protein. Crosslinking of the Porimin receptor expressed on COS7 transfectants resulted in the loss of cell membrane integrity and cell death as measured by the leakage of intracellular lactate dehydrogenase. Both COS7 and 293 cells expressing transfected Porimin at a relatively high level lost their ability to adhere to culture dishes, suggesting a role for Porimin in cell adhesion. ThePorimingene was mapped to human chromosome 11q22.1 and is composed of four exons spanning 133 kb of genomic DNA.
Capacitance cytometry: Measuring biological cells one by one
Authors: Sohn L. L. , Saleh O. A. , Facer G. R. , Beavis A. J. , Allan R. S. , Notterman D. A.
Published: July 2002

Measuring the DNA content of eukaryotic cells is a fundamental task
in biology and medicine. We have observed a linear relationship between
the DNA content of eukaryotic cells and the change in capacitance that
is evoked by the passage of individual cells across a 1-kHz electric
field. This relationship is species-independent; consequently, we have
developed a microfluidic technique—“capacitance cytometry”—that
can be used to quantify the DNA content of single eukaryotic cells and
to analyze the cell-cycle kinetics of populations of cells. Comparisons
with standard flow cytometry demonstrate the sensitivity of this new
technique.
Deep-Earth reactor: Nuclear fission, helium, and the geomagnetic field
Authors: Hollenbach D. F. , Herndon J. M.
Published: July 2002

Geomagnetic field reversals and changes in intensity are
understandable from an energy standpoint as natural consequences of
intermittent and/or variable nuclear fission chain reactions deep
within the Earth. Moreover, deep-Earth production of helium, having
3
He/
4
He ratios within the range observed from
deep-mantle sources, is demonstrated to be a consequence of nuclear
fission. Numerical simulations of a planetary-scale geo-reactor were
made by using the SCALE sequence of codes. The results clearly
demonstrate that such a geo-reactor (
i
) would function
as a fast-neutron fuel breeder reactor; (
ii
) could,
under appropriate conditions, operate over the entire period of
geologic time; and (
iii
) would function in such a manner
as to yield variable and/or intermittent output power.
Population structure and history in East Asia
Authors: Ding Yuan-Chun , Wooding Stephen , Harpending Henry C. , Chi Han-Chang , Li Hai-Peng , Fu Yun-Xin , Pang Jun-Feng , Yao Yong-Gang , Yu Jing-Gong Xiang , Moyzis Robert , Zhang Ya-ping
Published: July 2002

Archaeological, anatomical, linguistic, and genetic data have
suggested that there is an old and significant boundary between the
populations of north and south China. We use three human genetic marker
systems and one human-carried virus to examine the north/south
distinction. We find no support for a major north/south division in
these markers; rather, the marker patterns suggest simple isolation by
distance.
Efficient transduction of neural cells
in vitro
and
in vivo
by a baculovirus-derived vector
Authors: Sarkis C. , Serguera C. , Petres S. , Buchet D. , Ridet J.-L. , Edelman L. , Mallet J.
Published: July 2002

Gene delivery to the central nervous system is central to the
development of gene therapy for neurological diseases. We developed a
baculovirus-derived vector, the Bac-CMV-GFP vector, containing a
reporter gene encoding for the green fluorescent protein (GFP) under
the control of the cytomegalovirus (CMV) promoter. Two neuroblastomal
cell lines and three human primary neural cultures could be efficiently
transduced. In all cases, addition of butyrate, an inhibitor of histone
deacetylase, increased the level of expression in terms of the number
of GFP-expressing cells and the intensity of fluorescence. The level of
expression in a human telencephalic culture was over 50% of transduced
cells with a multiplicity of infection of 25. GFP expression was
demonstrated to be genuine expression and not pseudotransduction of the
reporter protein. Most interestingly, Bac-CMV-GFP could transduce
neural cells
in vivo
when directly injected into the
brain of rodents and was not inactivated by the complement system.
Thus, baculovirus is a promising tool for gene transfer into the
central nervous system both for studies of the function of foreign
genes and the development of gene therapy strategies.
Specific interference with gene expression induced by long, double-stranded RNA in mouse embryonal teratocarcinoma cell lines
Authors: Billy Eric , Brondani Vincent , Zhang Haidi , Müller Ulrich , Filipowicz Witold
Published: July 2002

In eukaryotes, double-stranded (ds) RNA induces sequence-specific
inhibition of gene expression, referred to as RNA interference
(RNAi). In invertebrates, RNAi can be triggered effectively by either
long dsRNAs or 21- to 23-nt-long short interfering (si) duplex RNAs,
acting as effectors of RNAi. siRNAs recently have been shown to act as
potent inducers of RNAi in cultured mammalian cells. However, studies
of RNAi activated by long dsRNA are impeded by its nonspecific effects,
mediated by dsRNA-dependent protein kinase PKR and RNase L. Here, we
report that the RNAi response can be induced effectively by long dsRNA
in nondifferentiated mouse cells grown in culture. Transfection of
dsRNA into embryonal carcinoma (EC) P19 and F9 cells results in a
sequence-specific decrease in the level of proteins expressed from
either exogenous or endogenous genes. dsRNA-mediated
inhibition of the reporter gene also occurs in mouse embryonic stem
cells. The RNAi effect is mediated by siRNAs, which are generated by
cleavage of dsRNA by the RNaseIII-like enzyme, Dicer. We demonstrate
that extracts prepared from EC cells catalyze processing of dsRNA into
≈23-nt fragments and that Dicer localizes to the cytoplasm of EC and
HeLa cells.
Epitope-specific tolerance induction with an engineered immunoglobulin.
Authors: Zambidis E T , Scott D W
Published: July 2002

Isologous and heterologous immunoglobulins have been shown to be extremely effective as tolerogenic carriers for nearly 30 years. The efficacy of these proteins is due in part to their long half-life in vivo, as well as their ability to crosslink surface IgM with Fc receptors. The concept of using IgG as a carrier molecule to induce unresponsiveness in the adult immune system has been exploited for simple haptens, such as nucleosides, as well as for peptides. To further evaluate the in vivo potential of these molecules for inducing tolerance to a defined epitope, we have engineered a fusion protein of mouse IgG1 with the immunodominant epitope 12-26 from bacteriophage lambda cI repressor protein. This 15-mer, which contains both a B-cell and T-cell epitope, has been fused in-frame to the N terminus of a mouse heavy chain IgG1 construct, thus creating a "genetic hapten-carrier" system. We describe a novel in vitro and in vivo experimental system for studying the feasibility of engineered tolerogens, consisting of a recombinant flagellin challenge antigen and a murine IgG1 tolerogen, both expressing the lambda repressor epitope 12-26. Herein, we show that peptide-grafted IgG molecules injected i.v., or expressed by transfected, autologous B cells, can efficiently modulate the cellular and humoral immune responses to immunodominant epitopes. This model displays the feasibility of "tailor-designing" immune responses to whole antigens by selecting epitopes for either tolerance or immunity.