bluuebunny/crossref_metadata_2025 huggingface dataset:
Peculiarities of thermodynamics of 2D Heisenberg magnets on a triangular lattice
Authors: Antsygina T. N.
Published: July 2002

Thermodynamic and magnetic properties of 2D Heisenberg ferro- and antiferromagnets with a spin of 1/2 on a triangular lattice are investigated theoretically. The formalism of two-time Green’s functions and the decoupling procedure explicitly taking into account the presence of a short-range order and not requiring the existence of a long-range order in the system are used. The energy, heat capacity, and susceptibility of magnets are expressed in terms of correlation functions for which a self-consistent system of equations is obtained. The system is solved numerically in the entire temperature range. Analytic asymptotic forms of the above quantities are constructed in the limits of high and low temperatures. The results of analysis are compared with analogous data for square lattices as well as with the high-temperature expansions available in literature.
Dynamics of formation of soliton conductivity in a 2D-array of linear chains containing commensurate charge density waves near the contact with a normal metal
Authors: Pershin Yurij V. , Rozhavsky Alexander S.
Published: July 2002

We make a numerical study of the conversion of conduction electrons into charge density wave (CDW) topological solitons at the interface between a normal metal and a 2D-array of the CDW-carrying linear chains. The interplay of commensurability potential, interchain interaction, and electric field on the dynamics of soliton formation is studied. When the interchain interaction exceeds the commensurability energy, the dynamic mechanism of creation of fractionally charged solitons near the contact is suppressed and specific contact nonlinearity in transport current is not observed.
Superconducting and normal properties of the set of Mo/Si superlattices with variable Si layer thickness
Authors: Mikhaı̆lov M. Yu. , Yuzephovich O. I. , Pokhila A. S. , Bomze Yu. V. , Fogel N. Ya. , Dmitrenko I. M. , Yulin S. A. , Sidorenko A. S. , Moldovan O. B. , Buchstab E. I.
Published: July 2002

We report the results of the superconducting and kinetic parameter measurements (transition temperature Tc, parallel and perpendicular critical fields Hc2, resistivity in the normal state) on a set of Mo/Si superconducting superlattices with a constant metal layer thickness dMo=22 Å and variable semiconducting one dSi(14–44 Å). Our data show a monotonic dependence of all measured parameters on dSi. It is found that the Josephson interlayer coupling energy depends exponentially on the spacer thickness. The data obtained allowed us to determine the characteristic electron tunneling length for amorphous silicon with high precision. It is equal to 3.9 Å. Enhancement of interlayer coupling leads to the Mo. Si multilayer transition temperature increasing, in agreement with Horovitz theory and with the experimental data on high-Tc materials.
The state of mercury vacancies in semimagnetic semiconductor Hg1−x−yCdxMnyTe
Authors: Prozorovskii V. D. , Reshidova I. Yu.
Published: July 2002

It is established directly, on the basis of investigations of the Shubnikov–de Haas effect at microwave frequencies and nonresonance cyclotron absorption in solid solution of semimagnetic semiconductor Hg1−x−yCdxMnyTe, that resonant acceptor states associated with mercury vacancies of two types are present in its conduction band. The dependence of the ground state energy of these acceptors on the energy gap is in agreement with the theoretical concepts concerning the long-range Coulomb potential of mercury vacancies.
The role of chemical disorder in the magnetism of YbInCu4 compound
Authors: Svechkarev I. V. , Dolya S. N.
Published: July 2002

It is found that chemical disorder in the YbInCu4 compound (especially in the Yb sublattice) considerably affects its magnetic properties due to spatial nonuniformity of the temperature TV of the first-order valence phase transition. The evolution of the magnetic susceptibility during disordering of the stoichiometric compound YbInCu4 is described by the model expression taking into account the TV dispersion upon the application of pressure and variation of composition of YbIn1−xAgxCu4 solid mixtures. The behavior of the main parameters of the system masked by blurring of the magnetic susceptibility singularity for a disordered sample during phase transition. Among other things, the value of the derivative dTV/dx=203 K is determined. The reason behind an abrupt change in the concentration dependence of dispersion and the paramagnetic Curie temperature is calculated at xc≃0.25.
Nonstationary effects induced by a strong direct current in a compensated metal
Authors: Tkachev G. B.
Published: July 2002

The existence of nonstationary electromagnetic processes in a plate of compensated metal carrying a strong direct current is established theoretically. The nonstationary effects are due to the nonlinearity caused by the influence of a inhomogeneous sign-alternating magnetic field of the current on the dynamics of charge carriers. Such an influence suppresses conductivity in the entire sample except a narrow region near the zero magnetic field plane. It is found that the current pinch formed in this region can propagate quasi-statically in the direction transverse to the current. As a result, an ac electric field component (and hence, an ac voltage across the sample across the sample) appears against the background of the applied dc electric field. The ac voltage generation can be observed experimentally in a preset current mode.
Phenomenological model for Casimir attraction of a metal film
Authors: Dubrava V. N. , Yampol’skiı̆ V. A.
Published: July 2002

The force of surface interaction (Casimir effect) between a bulk conductor and a metal film deposited on a dielectric substrate is studied by the method of quantum field theory. The film thickness is assumed to be much smaller than the skin depth at characteristic frequencies of fluctuation fields. The equations for one-particle Green’s function of the electromagnetic field in the metal film are solved on the basis of a simple phenomenological model. Namely, complex macroscopic electrodynamic properties of the film are described by introducing the surface permittivity determined by the conductivity 〈σ〉 averaged over sample thickness. The dependence of the Casimir attractive force on the specularity parameter ρ characterizing the interaction of conduction electrons with the film surface is predicted. The results of investigations demonstrate that the electronic and surface properties of metal films can in principle be studied experimentally by measuring the force of their Casimir attraction.
Green function of fermions in 2D superconducting Fröhlich model with inhomogeneous order parameter
Authors: Loktev V. M. , Turkowski V. M.
Published: July 2002

The fermion Green function and spectral characteristics for the 2D Fröhlich model of superconductivity at static fluctuations in the phase of the order parameter are calculated. The results demonstrate strongly non-Fermi-liquid properties of the system at finite temperatures and relate with the pseudogap behavior of high-Tc superconductors at relatively small charge carrier densities.
Dislocation-related inelastic phenomena at different damping levels
Authors: Beloshapka V. Ya. , Gur’yanov V. G. , Platkov V. Ya.
Published: July 2002

A numerical investigation is made into the dynamics of steady-state oscillations of an isolated dislocation loop over a wide interval of forced oscillation frequencies and at different levels of damping. The dependence of the dislocation-related strain and power dissipation on the external stress is found for different levels of damping. The amplitude dependences of such integral characteristics of the dynamics of dislocation motion as the internal friction, the elastic-modulus defect, and the ratio of the two are investigated. A critical value of the damping level of the dislocation loop is found at which the dislocation hysteresis begins to lose its static character and starts to take on dynamic traits. The features of the formation of dislocation hysteresis under conditions of its transformation from a static to a dynamic type are established.
Nuclear spin–spin relaxation in He3–4He two-phase solid solutions at ultralow temperatures
Authors: Mikhin N. P. , Polev A. V. , Rudavskii E. Ya. , Syrnikov Ye. V. , Shvarts V. A.
Published: July 2002

The spin–spin relaxation time in a He3–4He solid solution is measured before and after phase separation in the temperature range 1–250 mK. The spin echo technique is used, which permits separating the contributions of the two separated phases to the magnetic relaxation. It is found that in the concentrated phase the spin–spin relaxation time is practically independent of temperature above 50 mK and is described by the same exchange mechanisms as in pure He3. In the dilute phase the relaxation time is inversely proportional to the concentration and agrees with the corresponding values for homogeneous solutions. The dominant contribution to the spin–spin relaxation process is from He3–4He tunneling exchange. At the lowest temperatures the spin echo exhibits anomalous behavior, which may be a manifestation of quasi-one-dimensional diffusion.
Compensation effects in the interaction of the electron and ion subsystems of a metal
Authors: Tsymbal L. T. , Cherkasov A. N. , Panchenko O. F.
Published: July 2002

A detailed theoretical analysis is made of the interaction of the electron and ion subsystems in normal metals. Simple, but realistic models of the Fermi surface and deformation-potential tensor are used which permit numerical solution of the dispersion relation. To elucidate the consequences of the partial or total mutual compensation of the electron and hole concentrations, both the external parameters (sound frequency, magnetic field) and the model parameters for the metal (the constant of the deformation-potential tensor, the ratio of electron and hole concentrations, the free carrier relaxation rate) are varied. It is shown that in compensated metals the compensation effects lead to strong suppression of the interaction of the lattice with one of the groups of free carriers. The theoretical results are in qualitative agreement with the experimental data obtained in cadmium and tungsten. A quantitative comparison of the theory with experiment is carried out which, in particular, yields an estimate for the values of the constants of the deformation potential in cadmium.
Hot electrons in nanocontacts
Authors: Kulinich S. I. , Shekhter R. I. , Krive I. V. , Kulinich S. I. , Krive I. V.
Published: July 2002

A theoretical study is made of the temperature of the electron subsystem in a microcontact as a function of the applied voltage. It is shown that in microcontacts whose characteristic linear dimension is of the order of several lattice constants (nanocontacts) a breakdown of thermodynamic equilibrium between the electrons and phonons occurs at high applied voltages. Then the temperature of the electron subsystem is a linear function of the applied voltage, and its absolute magnitude can reach values of the order of the Fermi energy. These results agree with recent experimental data.
Differential diffusion of passive scalars in isotropic turbulence
Authors: Yeung P. K. , Pope S. B.
Published: July 2002

The differential diffusion of passive scalars of different molecular diffusivities is studied by performing direct numerical simulations of scalar fields in statistically stationary isotropic turbulence at Taylor-scale Reynolds number 38. Starting from identical initial conditions, each scalar field eventually becomes self-similar, with constant length scale and with its variance decaying exponentially with time. This decay rate depends weakly on the diffusivity. The correlation coefficient between two scalars initially decreases rapidly, but subsequently evolves much more slowly. The scalars ultimately become completely decorrelated at all scales. The scale dependency of correlation is studied through the coherency spectrum, which is affected only indirectly by the diffusivity difference. A Fourier-spectral approach emphasizes the importance of interscale spectral transfer of multiple scalars due to turbulent advection. Small-time behavior is compared with an analysis based on the diffusion equation.
Absolute and convective instability of axisymmetric jets with external flow
Authors: Jendoubi S. , Strykowski P. J.
Published: July 2002

The stability of an axisymmetric jet was examined in the presence of external co-flow and counterflow. Spatio-temporal theory was used to distinguish regions of absolute and convective instability in a parameter space including the velocity ratio, density ratio, Mach number, and the shear layer thickness. The absolute-convective transition was identified for two distinct axisymmetric modes. One of these modes became absolutely unstable in the presence of ambient co-flow while the other mode required external counterflow to admit an absolutely unstable solution. In general, the former mode was most unstable in low density jets, while the latter became more unstable as the jet density was increased relative to the surrounding fluid. In the range of parameters studied, both modes became increasingly unstable with decreasing jet density and for lower Mach numbers. The results of the spatiotemporal theory are also compared to globally unstable modes identified in laboratory jets.
Effects of heat release on triple flames
Authors: Ruetsch G. R. , Vervisch L. , Liñán A.
Published: July 2002

Heat release effects on laminar flame propagation in partially premixed flows are studied. Data for analysis are obtained from direct numerical simulations of a laminar mixing layer with a uniformly approaching velocity field. The structure that evolves under such conditions is a triple flame, which consists of two premixed wings and a trailing diffusion flame. Heat release increases the flame speed over that of the corresponding planar premixed flame. In agreement with previous analytical work, reductions in the mixture fraction gradient also increase the flame speed. The effects of heat release and mixture fraction gradients on flame speed are not independent, however; heat release modifies the effective mixture fraction gradient in front of the flame. For very small mixture fraction gradients, scaling laws that determine the flame speed in terms of the density change are presented.
Pattern transitions induced by the surface properties of suspended microspheres in electrorheological fluid
Authors: Wen Weijia , Lu Kunquan
Published: July 2002

In our previous Letter [Phys. Fluids 8, 2789 (1996)] we reported a new kind of netlike structure formed by metal microspheres suspended in silicon oil. In this paper we present further experimental results showing that different patterns are formed depending on whether metal, semiconducting, or dielectric microspheres are presented in the electric field. In addition, several experiments are performed on the surface properties of suspended microspheres and it is found that a pattern transition occurs when the surface conductivity of the solid phase is changed. This phenomenon can also be observed in a glass/oil ER fluid if the glass particles absorb enough water.
Flow control of vortex shedding by a short splitter plate asymmetrically arranged downstream of a cylinder
Authors: Ozono S.
Published: July 2002

The flow around a circular cylinder (diameter d) was investigated, behind which a short thin splitter plate with a chord of 1.0d was inserted horizontally as an interference element. The plate was traversed upstream along the wake; hence its relative position is defined by gap G from the cylinder base to the plate tip and by level Z from the wake centerline. The variation in both base suction coefficient and Strouhal number with G/d significantly depends on Z/d. In the circular cylinder case with Z/d=0.5–1.3, as the plate approaches the cylinder, the base suction coefficient exhibits a critical fall in a similar fashion to Roshko’s experiment where Z/d=0. Interestingly, however, unlike his experiment, the Strouhal number exceeds the natural one for some range of G/d beyond the critical gap. To further examine the flow mechanism, a similar situation was investigated by using a rectangular cylinder (height h, depth 0.1h) in place of the circular cylinder. A rise in the Strouhal number is observed for Z/h=1.1. These rises in Strouhal number are explained by the flow mode in which the shear layer separated from the gap side is forced to flow into the gap and to interact in the nearer wake by the approach of the splitter plate.
Response to ‘‘Comment on ‘Electron acoustic surface waves in a two-electron component plasma’ ’’ [Phys. Fluids B 5, 4502 (1993)]
Authors: Bharuthram R. , Misthry S. S. , Yu M. Y.
Published: July 2002

Three points are discussed: (a) the models of boundary conditions; (b) the mean velocity of hot electrons and their density; (c) the validity of the term ‘‘electron acoustic waves.’’ (AIP)
Localization of slow magnetosonic waves in the solar corona
Authors: Rutkevich I. M. , Mond M.
Published: July 2002

The propagation and localization of slow magnetosonic waves (SMW) in a radially nonuniform pnasma column in the presence of an axial magnetic field are investigated. A magnetohydrodynamic (MHD) model that is appropriate for the conditions in the hot solar cor/.al loops is emrloyed. It is shown that temperature nonuniformities give rise to channeling /f the SMW along magnetic field lmnes. The eigenvalue equation for the localized SMW is eerived qnd dependencies of the axial wave numbers and of the radii of localization on the wave frequency are presented for typical solar corona conditions. It is shown that the maximal radius of localization of the SMW is smaller than the observed radii of the loops. The effects of finite ion gyrofrequency are investigated by introducing the Hall dispersion term into the ideal MHD model. It is shown that the singular behavior of the ideal MHD continuous spectrum due to the slow magnetosonic resonance is not reproduced in the limit of small wave frequency to gyrofrequency ratio. This results in an increase of the maximal radius of localization.
Role of gob-5 in mucus overproduction and airway hyperresponsiveness in asthma
Authors: Nakanishi Atsushi , Morita Shigeru , Iwashita Hiroki , Sagiya Yoji , Ashida Yasuko , Shirafuji Hideo , Fujisawa Yukio , Nishimura Osamu , Fujino Masahiko
Published: July 2002

Airway hyperresponsiveness (AHR), goblet cell metaplasia, and mucus
overproduction are important features of bronchial asthma. To elucidate
the molecular mechanisms behind these pulmonary pathologies, we
examined for genes preferentially expressed in the lungs of a murine
model of allergic asthma by using suppression subtractive hybridization
(SSH). We identified a gene called
gob-5
that had a
selective expression pattern in the airway epithelium with AHR. Here,
we show that
gob-5
, a member of the calcium-activated
chloride channel family, is a key molecule in the induction of
murine asthma. Intratracheal administration of adenovirus-expressing
antisense
gob-5
RNA into AHR-model mice efficiently
suppressed the asthma phenotype, including AHR and mucus
overproduction. In contrast, overexpression of
gob-5
in
airway epithelia by using an adenoviral vector exacerbated the asthma
phenotype. Introduction of either
gob-5
or
hCLCA1
, the human counterpart of
gob-5
,
into the human mucoepidermoid cell line NCI-H292 induced mucus
production as well as
MUC5AC
expression. Our results
indicated that
gob-5
may play a critical role in murine
asthma, and its human counterpart
hCLCA1
is therefore a
potential target for asthma therapy.
Traumatic insemination and sexual conflict in the bed bug
Cimex lectularius
Authors: Stutt Alastair D. , Siva-Jothy Michael T.
Published: July 2002

The bed bug,
Cimex lectularius
, has a unique mode of
copulation termed “traumatic” insemination [Carayon, J. (1966)
in
Monograph of the Cimicidae
, ed. Usinger, R. (Entomol.
Soc. Am., Philadelphia), pp. 81–167] during which the male pierces
the female's abdominal wall with his external genitalia and
inseminates into her body cavity [Carayon, J. (1966) in
Monograph of the Cimicidae
, ed. Usinger, R. (Entomol.
Soc. Am., Philadelphia), pp. 81–167]. Under controlled natural
conditions, traumatic insemination was frequent and temporally
restricted. We show for the first time, to our knowledge, that
traumatic insemination results in (
i
) last-male sperm
precedence, (
ii
) suboptimal remating frequencies for the
maintenance of female fertility, and (
iii
) reduced
longevity and reproductive success in females. Experimental females did
not receive indirect benefits from multiple mating. We conclude that
traumatic insemination is probably a coercive male copulatory strategy
that results in a sexual conflict of interests.
The role of spatiotemporal edges in visibility and visual masking
Authors: Macknik Stephen L. , Martinez-Conde Susana , Haglund Michael M.
Published: July 2002

What parts of a visual stimulus produce the greatest neural signal? Previous studies have explored this question and found that the onset of a stimulus's edge is what excites early visual neurons most strongly. The role of inhibition at the edges of stimuli has remained less clear, however, and the importance of neural responses associated with the termination of stimuli has only recently been examined. Understanding all of these spatiotemporal parameters (the excitation and inhibition evoked by the stimulus's onset and termination, as well as its spatial edges) is crucial if we are to develop a general principle concerning the relationship between neural signals and the parts of the stimulus that generate them. Here, we use visual masking illusions to explore this issue, in combination with human psychophysics, awake behaving primate neurophysiology in the lateral geniculate nucleus of the thalamus, and optical recording in the primary visual cortex of anesthetized monkeys. The edges of the stimulus, rather than its interior, generate the strongest excitatory and inhibitory responses both perceptually and physiologically. These edges can be imaged directly by using optical recording techniques. Excitation and inhibition are moreover most powerful when the stimulus turns both on and off (what might be thought of as the stimulus's temporal edges). We thus conclude that there is a general principle that relates the generation of neural signals (excitatory and inhibitory) to the spatiotemporal edges of stimuli in the early visual system.
Effects of mutations involving cell division, recombination, and chromosome dimer resolution on a
priA2
∷
kan
mutant
Authors: McCool Jesse D. , Sandler Steven J.
Published: July 2002

Recombinational repair of replication forks can occur either to a crossover (XO) or noncrossover (non-XO) depending on Holliday junction resolution. Once the fork is repaired by recombination, PriA is important for restarting these forks in
Escherichia coli
. PriA mutants are Rec
−
and UV sensitive and have poor viability and 10-fold elevated basal levels of SOS expression.
PriA sulB
mutant cells and their nucleoids were studied by differential interference contrast and fluorescence microscopy of 4′,6-diamidino-2-phenylindole-stained log phase cells. Two populations of cells were seen. Eighty four percent appeared like wild type, and 16% of the cells were filamented and had poorly partitioned chromosomes (Par
−
). To probe potential mechanisms leading to the two populations of cells, mutations were added to the
priA sulB
mutant. Mutating
sulA
or introducing
lexA3
decreased, but did not eliminate filamentation or defects in partitioning. Mutating either
recA
or
recB
virtually eliminated the Par
−
phenotype. Filamentation in the
recB
mutant decreased to 3%, but increased to 28% in the
recA
mutant. The ability to resolve and/or branch migrate Holliday junctions also appeared crucial in the
priA
mutant because removing either
recG
or
ruvC
was lethal. Lastly, it was tested whether the ability to resolve chromosome dimers caused by XOs was important in a
priA
mutant by mutating
dif
and the C-terminal portion of
ftsK
. Mutation of
dif
showed no change in phenotype whereas
ftsK1
∷
cat
was lethal with
priA2
∷
kan
. A model is proposed where the PriA-independent pathway of replication restart functions at forks that have been repaired to non-XOs.
Action potentials reliably invade axonal arbors of rat neocortical neurons
Authors: Cox Charles L. , Denk Winfried , Tank David W. , Svoboda Karel
Published: July 2002

Neocortical pyramidal neurons have extensive axonal arborizations that make thousands of synapses. Action potentials can invade these arbors and cause calcium influx that is required for neurotransmitter release and excitation of postsynaptic targets. Thus, the regulation of action potential invasion in axonal branches might shape the spread of excitation in cortical neural networks. To measure the reliability and extent of action potential invasion into axonal arbors, we have used two-photon excitation laser scanning microscopy to directly image action-potential-mediated calcium influx in single varicosities of layer 2/3 pyramidal neurons in acute brain slices. Our data show that single action potentials or bursts of action potentials reliably invade axonal arbors over a range of developmental ages (postnatal 10–24 days) and temperatures (24°C-30°C). Hyperpolarizing current steps preceding action potential initiation, protocols that had previously been observed to produce failures of action potential propagation in cultured preparations, were ineffective in modulating the spread of action potentials in acute slices. Our data show that action potentials reliably invade the axonal arbors of neocortical pyramidal neurons. Failures in synaptic transmission must therefore originate downstream of action potential invasion. We also explored the function of modulators that inhibit presynaptic calcium influx. Consistent with previous studies, we find that adenosine reduces action-potential-mediated calcium influx in presynaptic terminals. This reduction was observed in all terminals tested, suggesting that some modulatory systems are expressed homogeneously in most terminals of the same neuron.
Opposing cardioprotective actions and parallel hypertrophic effects of δPKC and ɛPKC
Authors: Chen Leon , Hahn Harvey , Wu Guangyu , Chen Che-Hong , Liron Tamar , Schechtman Deborah , Cavallaro Gabriele , Banci Lucia , Guo Yiru , Bolli Roberto , Dorn Gerald W. , Mochly-Rosen Daria
Published: July 2002

Conflicting roles for protein kinase C (PKC) isozymes in cardiac
disease have been reported. Here, δPKC-selective activator and
inhibitor peptides were designed rationally, based on molecular
modeling and structural homology analyses. Together with previously
identified activator and inhibitor peptides of ɛPKC, δPKC peptides
were used to identify cardiac functions of these isozymes. In isolated
cardiomyocytes, perfused hearts, and transgenic mice, δPKC and ɛPKC
had opposing actions on protection from ischemia-induced damage.
Specifically, activation of ɛPKC caused cardioprotection whereas
activation of δPKC increased damage induced by ischemia
in
vitro
and
in vivo
. In contrast, δPKC and
ɛPKC caused identical nonpathological cardiac hypertrophy; activation
of either isozyme caused nonpathological hypertrophy of the heart.
These results demonstrate that two related PKC isozymes have both
parallel and opposing effects in the heart, indicating the danger in
the use of therapeutics with nonselective isozyme inhibitors and
activators. Moreover, reduction in cardiac damage caused by ischemia by
perfusion of selective regulator peptides of PKC through the coronary
arteries constitutes a major step toward developing a therapeutic agent
for acute cardiac ischemia.
Antimicrobial activity of MHC class I-restricted CD8+ T cells in human tuberculosis
Authors: Cho Sungae , Mehra Vijay , Thoma-Uszynski Sybille , Stenger Steffen , Serbina Natalya , Mazzaccaro Richard J. , Flynn JoAnne L. , Barnes Peter F. , Southwood Scott , Celis Esteban , Bloom Barry R. , Modlin Robert L. , Sette Alessandro
Published: July 2002

Studies of mouse models of tuberculosis (TB) infection have indicated a central role for MHC class I-restricted CD8+ T cells in protective immunity. To define antigens and epitopes ofMycobacterium tuberculosis(MTB) proteins that are presented by infected cells to CD8+ T cells, we screened 40 MTB proteins for HLA class I A*0201-binding motifs. Peptides that bound with high affinity to purified HLA molecules were subsequently analyzed for recognition by CD8+ cytotoxic T lymphocytes. We identified three epitopes recognized by CD8+ T cells from patients recovering from TB infection. Those three epitopes were derived from three different antigens: thymidylate synthase (ThyA30–38), RNA polymerase β-subunit (RpoB127–135), and a putative phosphate transport system permease protein A-1 (PstA175–83). In addition, CD8+ T cell lines specific for three peptides (ThyA30–38, PstA175–83, and 85B15–23) were generated from peripheral blood mononuclear cells of normal HLA-A*0201 donors. These CD8+ T cell lines specifically recognized MTB-infected macrophages, as demonstrated by production of IFN-γ and lysis of the infected target cells. Finally, CD8+ cytotoxic T lymphocytes reduced the viability of the intracellular MTB, providing evidence that CD8+ T cell recognition of MHC class I-restricted epitopes of these MTB antigens can contribute to effective immunity against the pathogen.
Amplification of dopaminergic signaling by a positive feedback loop
Authors: Nishi Akinori , Bibb James A. , Snyder Gretchen L. , Higashi Hideho , Nairn Angus C. , Greengard Paul
Published: July 2002

Dopamine and cAMP-regulated phosphoprotein of
M
r
32,000 (DARPP-32) plays an obligatory
role in most of the actions of dopamine. In resting neostriatal slices,
cyclin-dependent kinase 5 (Cdk5) phosphorylates DARPP-32 at Thr-75,
thereby reducing the efficacy of dopaminergic signaling. We report here
that dopamine, in slices, and acute cocaine, in whole animals,
decreases the state of phosphorylation of striatal DARPP-32 at Thr-75
and thereby removes this inhibitory constraint. This effect of dopamine
is achieved through dopamine D1 receptor-mediated activation of
cAMP-dependent protein kinase (PKA). The activated PKA, by decreasing
the state of phosphorylation of DARPP-32-Thr-75, de-inhibits itself.
Dopamine D2 receptor stimulation has the opposite effect. The ability
of activated PKA to reduce the state of phosphorylation of
DARPP-32-Thr-75 is apparently attributable to increased protein
phosphatase-2A activity, with Cdk5 being unaffected. Together, these
results indicate that via positive feedback mechanisms, Cdk5
signaling and PKA signaling are mutually antagonistic.
Sensory deprivation without competition yields modest alterations of short-term synaptic dynamics
Authors: Finnerty Gerald T. , Connors Barry W.
Published: July 2002

Cortical maps express experience-dependent plasticity. However, the
underlying cellular mechanisms remain unclear. We have recently shown
that sensory deprivation results in large changes of the short-term
dynamics of excitatory synapses at the junction of deprived and spared
somatosensory (barrel) cortex, which may contribute to map
reorganization. A key issue is whether the alterations in short-term
synaptic dynamics are driven by a loss of sensory input or by
competition between deprived and spared inputs. Here, we report that
short-term dynamics of horizontal pathways in the middle of uniformly
deprived cortex change only modestly. Vertical intracortical pathways
were unaffected by deprivation. Our results suggest that uniform loss
of sensory activity has a limited effect on short-term synaptic
dynamics. We concluded that competition between sensory inputs is
necessary to produce large-scale changes in synaptic dynamics after
sensory deprivation.
Reversible visual hemineglect.
Authors: Payne B R , Lomber S G , Geeraerts S , van der Gucht E , Vandenbussche E
Published: July 2002

We have identified a limited region in the posterior, but not anterior, half of the cat's middle suprasylvian region which, when cooled and inactivated unilaterally, results in a profound visual neglect of stimuli introduced into the contracooled hemifield. The severity of the deficit matches that induced by unilateral cooling of the superior colliculus. The cortical region is located at the temporo-occipito-parietal junction and is believed to be equivalent to a region centered on or close to the area V5 complex of primates.
Correction of diabetic alterations by glucokinase.
Authors: Ferre T , Pujol A , Riu E , Bosch F , Valera A
Published: July 2002

Hyperglycemia is a common feature of diabetes mellitus. It results from a decrease in glucose utilization by the liver and peripheral tissues and an increase in hepatic glucose production. Glucose phosphorylation by glucokinase is an initial event in glucose metabolism by the liver. However, glucokinase gene expression is very low in diabetic animals. Transgenic mice expressing the P-enolpyruvate carboxykinase/glucokinase chimeric gene were generated to study whether the return of the expression of glucokinase in the liver of diabetic mice might prevent metabolic alterations. In contrast to nontransgenic mice treated with streptozotocin, mice with the transgene previously treated with streptozotocin showed high levels of both glucokinase mRNA and its enzyme activity in the liver, which were associated with an increase in intracellular levels of glucose 6-phosphate and glycogen. The liver of these mice also showed an increase in pyruvate kinase activity and lactate production. Furthermore, normalization of both the expression of genes involved in gluconeogenesis and ketogenesis in the liver and the production of glucose and ketone body by hepatocytes in primary culture were observed in streptozotocin-treated transgenic mice. Thus, glycolysis was induced while gluconeogenesis and ketogenesis were blocked in the liver of diabetic mice expressing glucokinase. This was associated with normalization of blood glucose, ketone bodies, triglycerides, and free fatty acids even in the absence of insulin. These results suggest that the expression of glucokinase during diabetes might be a new approach to the normalization of hyperglycemia.
Identification of a pathogenicity island required for Salmonella survival in host cells.
Authors: Ochman H , Soncini F C , Solomon F , Groisman E A
Published: July 2002

We have identified a region unique to the Salmonella typhimurium chromosome that is essential for virulence in mice. This region harbors at least three genes: two (spiA and spiB) encode products that are similar to proteins found in type III secretion systems, and a third (spiR) encodes a putative regulator. A strain with a mutation in spiA was unable to survive within macrophages but displayed wild-type levels of epithelial cell invasion. The culture supernatants of the spi mutants lacked a modified form of flagellin, which was present in the supernatant of the wild-type strain. This suggests that the Spi secretory apparatus exports a protease, or a protein that can alter the activity of a secreted protease. The "pathogenicity island" harboring the spi genes may encode the virulence determinants that set Salmonella apart from other enteric pathogens.
Phenotypic and physiologic characterization of transgenic mice expressing interleukin 4 in the lung: lymphocytic and eosinophilic inflammation without airway hyperreactivity.
Authors: Rankin J A , Picarella D E , Geba G P , Temann U A , Prasad B , DiCosmo B , Tarallo A , Stripp B , Whitsett J , Flavell R A
Published: July 2002

To investigate the contribution of interleukin-4 (IL-4) to airway inflammation in vivo and to explore directly its relationship to airway reactivity, we created transgenic mice in which the murine cDNA for IL-4 was regulated by the rat Clara cell 10 protein promoter. Expression was detected only in the lung and not in thymus, heart, liver, spleen, kidney, or uterus. The expression of IL-4 elicited hypertrophy of epithelial cells of the trachea, bronchi, and bronchioles. Hypertrophy is due, at least in part, to the accumulation of mucus glycoprotein. Histologic examination of parenchyma revealed multinucleated macrophages and occasional islands of cells consisting largely of eosinophils or lymphocytes. Analysis of lung lavage fluid revealed the presence of a leukocytic infiltrate consisting of lymphocytes, neutrophils and eosinophils. Mice expressing IL-4 had greater baseline airway resistance but did not demonstrate hyperreactivity to methacholine. Thus, the expression of IL-4 selectively within the lung elicits an inflammatory response characterized by epithelial cell hypertrophy, and the accumulation of macrophages, lymphocytes, eosinophils, and neutrophils without resulting in an alteration in airway reactivity to inhaled methacholine.
Primary structure and tissue distribution of the orphanin FQ precursor.
Authors: Nothacker H P , Reinscheid R K , Mansour A , Henningsen R A , Ardati A , Monsma F J , Watson S J , Civelli O
Published: July 2002

The heptadecapeptide orphanin FQ (OFQ) is a recently discovered neuropeptide that exhibits structural features reminiscent of the opioid peptides and that is an endogenous ligand to a G protein-coupled receptor sequentially related to the opioid receptors. We have cloned both the human and rat cDNAs encoding the OFQ precursor proteins, to investigate whether the sequence relationships existing between the opioid and OFQ systems are also found at the polypeptide precursor level, in particular whether the OFQ precursor would encode several bioactive peptides as do the opioid precursors, and to study the regional distribution of OFQ sites of synthesis. The entire precursor protein displays structural homology to the opioid peptide precursors, especially preprodynorphin and preproenkephalin. The predicted amino acid sequence of the OFQ precursor contains a putative signal peptide and one copy of the OFQ sequence flanked by pairs of basic amino acid residues. Carboxyl-terminal to the OFQ sequence, the human and rat precursors contain a stretch of 28 amino acids that is 100% conserved and thus may encode novel bioactive peptides. Two peptides derived from this stretch were synthesized but were found to be unable to activate the OFQ receptor, suggesting that if they are produced in vivo, these peptides would likely recognize receptors different from the OFQ receptor. To begin analyzing the sites of OFQ mRNA synthesis, Northern analysis of human and rat tissues were carried out and showed that the OFQ precursor mRNA is mainly expressed in the brain. In situ hybridization of rat brain slices demonstrated a regional distribution pattern of the OFQ precursor mRNA, which is distinct from that of the opioid peptide precursors. These data confirm that the OFQ system differs from the opioid system at the molecular level, although the OFQ and opioid precursors may have arisen from a common ancestral gene.
Alteration of myosin cross bridges by phosphorylation of myosin-binding protein C in cardiac muscle.
Authors: Weisberg A , Winegrad S
Published: July 2002

In addition to the contractile proteins actin and myosin, contractile filaments of striated muscle contain other proteins that are important for regulating the structure and the interaction of the two force-generating proteins. In the thin filaments, troponin and tropomyosin form a Ca-sensitive trigger that activates normal contraction when intracellular Ca is elevated. In the thick filament, there are several myosin-binding proteins whose functions are unclear. Among these is the myosin-binding protein C (MBP-C). The cardiac isoform contains four phosphorylation sites under the control of cAMP and calmodulin-regulated kinases, whereas the skeletal isoform contains only one such site, suggesting that phosphorylation in cardiac muscle has a specific regulatory function. We isolated natural thick filaments from cardiac muscle and, using electron microscopy and optical diffraction, determined the effect of phosphorylation of MBP-C on cross bridges. The thickness of the filaments that had been treated with protein kinase A was increased where cross bridges were present. No change occurred in the central bare zone that is devoid of cross bridges. The intensity of the reflections along the 43-nm layer line, which is primarily due to the helical array of cross bridges, was increased, and the distance of the first peak reflection from the meridian along the 43-nm layer line was decreased. The results indicate that phosphorylation of MBP-C (i) extends the cross bridges from the backbone of the filament and (ii) increases their degree of order and/or alters their orientation. These changes could alter rate constants for attachment to and detachment from the thin filament and thereby modify force production in activated cardiac muscle.
Cloning, expression, and distribution of a Ca(2+)-activated K+ channel beta-subunit from human brain.
Authors: Tseng-Crank J , Godinot N , Johansen T E , Ahring P K , Strøbaek D , Mertz R , Foster C D , Olesen S P , Reinhart P H
Published: July 2002

We have cloned and expressed a Ca(2+)-activated K+ channel beta-subunit from human brain. The open reading frame encodes a 191-amino acid protein possessing significant homology to a previously described subunit cloned from bovine muscle. The gene for this subunit is located on chromosome 5 at band q34 (hslo-beta). There is no evidence for alternative RNA splicing of this gene product. hslo-beta mRNA is abundantly expressed in smooth muscle, but expression levels are low in most other tissues, including brain. Brain subregions in which beta-subunit mRNA expression is relatively high are the hippocampus and corpus callosum. The coexpression of hslo-beta mRNA together with hslo-alpha subunits in either Xenopus oocytes or stably transfected HEK 293 cells give rise to Ca(2+)-activated potassium currents with a much increased calcium and/or voltage sensitivity. These data indicate that the beta-subunit shows a tissue distribution different to that of the alpha-subunit, and in many tissues there may be no association of alpha-subunits with beta-subunits. These beta-subunits can play a functional role in the regulation of neuronal excitability by tuning the Ca2+ and/or the voltage dependence of alpha-subunits.
Differential synaptic localization of two major gamma-aminobutyric acid type A receptor alpha subunits on hippocampal pyramidal cells.
Authors: Nusser Z , Sieghart W , Benke D , Fritschy J M , Somogyi P
Published: July 2002

Hippocampal pyramidal cells, receiving domain specific GABAergic inputs, express up to 10 different subunits of the gamma-aminobutyric acid type A (GABAA) receptor, but only 3 different subunits are needed to form a functional pentameric channel. We have tested the hypothesis that some subunits are selectively located at subsets of GABAergic synapses. The alpha 1 subunit has been found in most GABAergic synapses on all postsynaptic domains of pyramidal cells. In contrast, the alpha 2 subunit was located only in a subset of synapses on the somata and dendrites, but in most synapses on axon initial segments innervated by axo-axonic cells. The results demonstrate that molecular specialization in the composition of postsynaptic GABAA receptor subunits parallels GABAergic cell specialization in targeting synapses to a specific domain of postsynaptic cortical neurons.
Abnormal phosphorylation of tau and the mechanism of Alzheimer neurofibrillary degeneration: Sequestration of microtubule-associated proteins 1 and 2 and the disassembly of microtubules by the abnormal tau
Authors: Alonso Alejandra del C. , Grundke-Iqbal Inge , Barra Héctor S. , Iqbal Khalid
Published: July 2002

The microtubule-associated protein (MAP) tau is abnormally hyperphosphorylated in Alzheimer disease and accumulates in neurons undergoing neurofibrillary degeneration. In the present study, the associations of the Alzheimer-hyperphosphorylated tau (AD P-tau) with the high molecular weight MAPs (HMW-MAPs) MAP1 and MAP2 were investigated. The AD P-tau was found to aggregate with MAP1 and MAP2 in solution. The association of AD P-tau to the MAPs resulted in inhibition of MAP-promoted microtubule assembly. However, unlike the coaggregation of AD P-tau and normal tau, the association between AD P-tau and the HMW-MAPs did not result in the formation of filaments/tangles. The affinity of the tau–AD P-tau association was higher than that of HMW-MAPs–AD P-tau because normal tau inhibited the latter binding. The association between AD P-tau and the HMW-MAPs also appeared to occur
in situ
because these proteins cosedimented from the Alzheimer brain extracts, and, in the sediment, the levels of the HMW-MAPs correlated with the levels of AD P-tau. These studies suggested that the abnormally phosphorylated tau can sequester both normal tau and HMW-MAPs and disassemble microtubules but, under physiological conditions, can form tangles of filaments only from tau.
“Willed action”: A functional MRI study of the human prefrontal cortex during a sensorimotor task
Authors: Hyder Fahmeed , Phelps Elizabeth A. , Wiggins Christopher J. , Labar Kevin S. , Blamire Andrew M. , Shulman Robert G.
Published: July 2002

Functional MRI (fMRI) was used to examine human brain activity within the dorsolateral prefrontal cortex during a sensorimotor task that had been proposed to require selection between several responses, a cognitive concept termed “willed action” in a positron emission tomography (PET) study by Frith
et al
. [Frith, C. D., Friston, K., Liddle, P. F. & Frackowiak, R. S. J. (1991)
Proc. R. Soc. London Ser. B
244, 241–246]. We repeated their sensorimotor task, in which the subject chooses to move either of two fingers after a stimulus, by fMRI experiments in a 2.1-T imaging spectrometer. Echo-planar images were acquired from four coronal slices in the prefrontal cortex from nine healthy subjects. Slices were 5 mm thick, centers separated by 7 mm, with nominal in-plane spatial resolution of 9.6 × 5.0 mm
2
for mean data. Our mean results are in agreement with the PET results in that we saw similar bilateral activations. The present results are compared with our previously published fMRI study of a verbal fluency task, which had also been proposed by Frith
et al
. to elicit a “willed action” response. We find a clear separation of activation foci in the left dorsolateral prefrontal cortex for the sensorimotor (Brodmann area 46) and verbal fluency (Brodmann area 45) tasks. Hence, assigning a particular activated region to “willed action” is not supported by the fMRI data when examined closely because identical regions are not activated with different modalities. Similar modality linked activations can be observed in the original PET study but the greater resolution of the fMRI data makes the modality linkages more definite.
Fixation of allosteric states of the nicotinic acetylcholine receptor by chemical cross-linking
Authors: Watty Anke , Methfessel Christoph , Hucho Ferdinand
Published: July 2002

Receptor activity can be described in terms of ligand-induced transitions between functional states. The nicotinic acetylcholine receptor (nAChR), a prototypic ligand-gated ion channel, is an “unconventional allosteric protein” which exists in at least three interconvertible conformations, referred to as resting (low agonist affinity, closed channel), activated (open channel), and desensitized (high agonist affinity, closed channel). Here we show that 3,3′-dimethyl suberimidate (DMS) is an agonistic bifunctional cross-linking reagent, which irreversibly “freezes” the nAChR in a high agonist affinity/closed-channel state. The monofunctional homologue methyl acetoimidate, which is also a weak cholinergic agonist, has no such irreversible effect. Glutardialdehyde, a cross-linker that is not a cholinergic effector, fixes the receptor in a low-affinity state in the absence of carbamoylcholine, but, like DMS, in a high-affinity state in its presence. Covalent cross-linking thus allows us to arrest the nAChR in defined conformational states.