bluuebunny/crossref_metadata_2025 huggingface dataset:
Expanding, homogeneous, ellipsoidal density perturbations. II. A simple theory for the acquisition of angular momentum by tidal torques
Authors: Caimmi R.
Published: July 2007

A simple theory is built up for the acquisition of angular momentum by tidal torques in expanding, homogeneous, ellipsoidal density perturbations from the epoch when inhomogencities begin to grow to the present epoch. The expansion is described according to an analytical approximation already known in the literature, which well holds before the turnaround of a sphere with same mass and initial overdensity as the ellipsoid, and holds no longer after a singular configuration (i.e., with a null volume) is attained by the above mentioned sphere. Though calculations at latest stages turn out to be physically meaningless, it is inferred that the spin growth during the virialized phase is negligible with respect to the spin growth during the expansion and relaxation phase. The evolution of typical inhomogeneities with initial axis ratios ϵ2i = 0.7, ϵ3i = 0.5 and masses MB = 1012 MȮ is computed, leading to: (i) a spin parameter λ = 0.054 at the beginning of strong decoupling from the Hubble flow, in cloes agreement with both analytical and numerical attempts related to different theories; (ii) an angular momentum J = 1.62 – 3.17 · 1075 g cm2 s−1 at the turnaround of a sphere with same mass and initial overdensity as the ellipsoid, within the correct order of magnitude deduced for the Galaxy; (iii) an angular momentum J ≈ 3 JD and J ≈ 2JD at the singular configuration and at the turnaround of the above mentioned sphere, respectively, with JD angular momentum gained before the strong decoupling from the Hubble flow. The features (i) and (iii) are common to all masses. The evolution of inhomogeneities with rms overdensities, same initial volume and typical galactic mass MB = 1012 MȮ is computed for a wide range of initial shapes, leading to an non‐dimensional angular momentum Λ with the following behaviour: (i) it is null for both spherical and flat or oblong configuration; (ii) it increases passing from prolate to oblate configurations with same minor axis; (iii) it changes passing from flat to prolate configurations with same middle axis, increasing or increasing and then decreasing according if prolate configurations are spindle‐like enough or ball‐like enough, repectively; (iv) the larger non‐dimensional spin growth occurs for oblate configurations with e3i ≈ 0.6. The above features are common to all masses and peak heights. In conclusion it cannot be asserted, but it may safely be expected, that (contrary to what happens in many other theories) no arbitrary cut‐off on tidal torques has to be advocated in the current theory, to yield an amount of angular momentum close to what has been deduced from observation. A complete answer on this point might come only from a more refined description of the expansion.
Cosmic strings and viscous matter in a Kantowski‐Sachs universe
Authors: Wolf C.
Published: July 2007

We study the dynamics of a universe where the matter content is represented by a radially directed distribution of cosmic strings plus matter admitting both shear and bulk viscosity. We assume specific forms for the equation of state of both the strings and matter and discuss the cosmological solutions obtained.
Revised orbital elements of minor planets
Authors: Scardia M. , Ghiringhelli D. , Debehogne H.
Published: July 2007

Revised orbital elements of minor planets 702 Alauda, 946 Poesia, 2395 Aho, 3051 Nantong, 3086 Kalbaugh and 4218 Demottoni are given.
Nearby galaxies. III. Gas–to–dust ratio in the interstellar medium of spiral and dwarf irregular galaxies
Authors: Schmidt K. H. , Boller T.
Published: July 2007

The gas‐to‐dust ratio in the interstellar medium of nearby spiral systems and dwarf irregular galaxies has been obtained by using mainly the compiled data by Schmidt and Boller (1992a). The gas‐to‐dust ratio of dwarf irregulars is larger by about one order of magnitude than for spiral galaxies, on the average. A relation between the gas‐to‐dust ratio and the metallicity, represented by the abundance of oxygen, has been detected.
Tidal effects of a massive spheroidal halo on an inner spheroidal contracting visible body: Application to an evolutionary disk‐galaxy model
Authors: Caimmi R. , Secco L.
Published: July 2007

The effects of the tidal interactions between two coaxial, homogeneous spheroids, one (the “Brigt Component”: B) completely embedded in the other (the “Dark Halo”: D), along a quasi‐static contraction, are considered. The aim is to look how the dynamical properties and the final morphology of the B subsystem may be affected by the presence of the D component. Three initial configurations are considered: the quasi‐spherical “Dark Halo” D coincides with the “Visible Component” B (case C); D is flatter than B but the two spheroids have the same semiminor axis (case N); no D component is assumed; the “visible” spheroid is single (case S). The application to an evolutionary disk‐galaxy model is considered under some simple assumptions: i) in cases C and N the spheroidal halo is massive (mass ratio “dark”/“bright” about ten) and dissipationless. For a mass ratio like this, the tidal interaction of the B component over D turns to be negligible in the course of the contraction; adding to that the lack of dissipation, it appears plausible to take the D component as frozen along the evolution; ii) the degree of anisotropy and the angular momentum of B, JB, are conserved. The conservation of JB provides us the time‐independent relationship among the key physical quantities and gives the possibility to draw the evolutionary tracks on the plane (axis ratio σB, semimajor axis aB) without any explicit time‐scale; iii) the global “star formation rate” is parametrized according to a simple “Schmidt power law” proportional to the square of gas density. At every step of the quasi‐static contraction, the structure is determined by the tensor virial theorem extended to a double configuration. The model is very idealized, particularly because there are no available tidal gravitational terms other than for the case of two homogeneous. Nevertheless, the method based on the tensor virial appears powerful to gain insight into the correlations among the physical quantities involved and into their trend along the evolution. One of the main result is a clear indication of a leading role played by the axis ratio of the “Dark‐Halo” component which might be, to the extent that this simple picture can be compared with a real galactic system, a possible new physical parameter to be added to mass and angular momentum for separating spirals from S0 galaxies.
The stability of tension stars
Authors: Wolf C.
Published: July 2007

By studying the cylindrically symmetric solution for matter in 2+1 space‐time dimensions we arrive at stability criteria for such a configuration when the local energy density is proportional to the square of the tension (negative pressure). Our analysis demonstrates that to the post‐Newtonian approximation that such a configuration is stable provided it does not shrink below a certain radius. We find our model provides a reason for how stars form from a two‐dimensional configuration with both a maximum mass and a minimum radius.
Beobachtungen Kleiner Planeten. XIII
Authors: Börngen F. , Schmadel L. D.
Published: July 2007

Es wird eine Übersicht gegeben über die im Jahr 1992 auf Tautenburger Schmidtplatten gefundenen Kleinen Planeten. Es wurden 518 Objekte beobachtet und für diese 2396 Positionen gerechnet. Es handelt sich um 408 Planetoiden mit provisorischer Bezeichnung, unter denen 274 neu vergebene Bezeichnungen sind, sowie um 110 numerierte Objekte. Für 172 Tautenburger Objekte wurden Bahnen aus einer Opposition gerechnet. Für 55 im Berichtszeitraum numerierte Planeten haben Tautenburger Positionen einen Beitrag geleistet. Acht Tautenburger Planetoiden wurden numeriert (Tab. 3). A summary is given about the Minor Planet survey performed in 1992 on Tautenburg Schmidt plates. 518 asteroids were observed and 2396 positions are calculated for them. These are 408 asteroids with provisional designations (274 of them have new designations) and 110 numbered objects. One‐opposition orbits have been computed for 172 Tautenburg asteroids. Tautenburg observations could give a contribution to 55 planets numbered in the period of this report. Eight Tautenburg asteroids have been numbered (Tab. 3).
Dynamics of dimensions in factor‐space cosmology
Authors: Bleyer U. , Rainer M. , Mohazzab M.
Published: July 2007

For multi‐dimensional cosmological models we investigate the dynamics of both, scales and dimensions. The classical equation of motions and the corresponding Wheeler‐de Witt equation are set up generally and the qualitative behaviour of the system is discussed for some specific model with 2 factor spaces: A space M1 with dynamical dimension, and a compact internal space M2 of constant dimension. With a natural choice of some contraint, there exist a solution where M1 expands as usual space while M2 is shrinking down to unobservable scales.
Schmidt plate survey towards the Galactic centre. 2. Stellar statistics in the direction of the Sagittarius‐Carina arm
Authors: Kharchenko N. , Schilbach E.
Published: July 2007

A study of the structure and kinematics of the Galaxy from Tautenburg Schmidt plates taken towards the Galactic centre (l = 17.0°, b = +0.8°) is presented. Proper motions and B, V magnitudes were determined for about 36 500 stars up to the limiting magnitude V = 16m.8 in a field of 8.95 square degrees. Proper motion accuracy of about 3 mas/year has been obtained for stars brighter than V = 15m. The rms errors of stellar magnitudes and (B–V) colours is about 0.1 mag.

The majority of field stars in the survey are main sequence stars and red giants of the disk. They belong to the Local or Sagittarius‐Carina arms, or they are located between these spiral arms. Comparing the modelled and observed distributions of magnitudes and colours, we specified the interstellar extinction determined in the preceding study of open clusters in this field.

The luminosity function towards the Galactic centre was determined for stars with absolute magnitudes from ‐4m.35 to +9m. Kinematical and spatial distribution parameters up to 4 kpc from the Sun were obtained as a function of galactocentric distance.
Photometric survey near the main Galactic meridian: 2.2. Finding charts and photoelectric UBVR stellar magnitudes in 26 fields
Authors: Andruk V. , Kharchenko N. , Schilbach E. , Scholz R.‐D.
Published: July 2007

Finding charts and photoelectric magnitudes of stars in the UBVR system in 26 fields of the MEGA programme are presented. This part of the photometric survey near the Main Galactic Meridian includes the fields with right ascentions 8h < α < 16h30m and declinations −2° < δ < 58°. Together with the finding charts of 2.5° × 2.5° the equatorial coordinates of the stars are given for epoch and equinox 1950. Photometric properties of the night sky at the Mount Terskol observatory near Mount Elbrus are derived from the photoelectric observations.
The irregular galaxy Cassiopeia 1 – a new member of the Local group
Authors: Tikhonov N.
Published: July 2007

A photometry in the V, R, I (Cousins) system has been performed for stars in the galaxy Cassiopeia 1. The resulting colour‐agnitude (CM) diagram of Cas 1 reveals the existence of blue stars and the absence of red ones. From an analysis of the CM diagram of the galaxy it is concluded that Av = 4.0 mag, and the distance modulus (m – M)o = 24.5 mag, corresponding to a distance of 790 kpc. The visual magnitude of the galaxy is V = 14m.62 (Mv = −13m.8) and the colour index (V – R) = 0.89 mag. From the distance determination the galaxy Cassiopeia 1 is a member of the Local group.
Nearby galaxies. IV. The global Hubble parameter and the dispersion of the Hubble relation
Authors: Schmidt K.‐H. , Karachentsev I. D.
Published: July 2007

Using a spherically symmetric model of the Virgo flow the global Hubble parameter has been estimated from the observed radial velocities and the photometrically measured distances of nearby galaxies. Adopting the observed recession velocity of the Virgo Cluster to about 1000 km s−1 and the infall velocity of the Local Group to 350 km s−1 the global Hubble constant results to 73 ± 10 km s−1 Mpc−1. This value corresponds with the distance of the Virgo Cluster of 18 ± 2 Mpc. The cosmic dispersion of the galaxies around the Hubble relation is of order of 35 km s−1.
Young stars in the disk of M82
Authors: Notni P. , Karachentsev I. , Makarova L.
Published: July 2007

We present CCD VIC photometry in a field 1.9 − 1.3 square arcmin and positioned about 3 arcmin north‐east of the centre of M82. More than 100 stars have been identified and measured above the photometric limits V = 23m.5, I = 22m. Most of the objects fainter than V ≈︁ 20m should be members of M82 as expected from the statistics of foreground stars.

Starlike as well as 2–3 somewhat diffuse objects ‐ candidates of globular clusters ‐ preferentially occupy yellow colours in the colour‐magnitude diagram; extreme blue and red objects are missing. The colour‐magnitude diagram indicates continuing star formation in this part of the disk. The absence of blue stars is caused by reddening; no convincing explanation is found for the missing red supergiants. Young stars are distributed throughout the whole field, the youngest being concentrated in associations at the SW edge of the field.

To cope with the very irregular background created by the galaxy' s main body and with the low contrast of many of the stars against this background, a modified photometric method is introduced in which the background is estimated using the intensities in a ring drawn very tightly around the star in the wings of the point spread function.
Fluxtube magnetic field measurements in a solar flare in comparison with non‐flare regions
Authors: Kostenko L. M. , Lozitskij V. G.
Published: July 2007

Measurements of the fluxtube field strength B and filling α in solar flares, active regions and faculae have been analyzed. To estimate the values of B, Stokes V peak separations of the Fe I 5247 Å and Fe I 5250 Å lines have been used. It was found that the value of B in an In‐flare (˜ 1.1 kG) was slightly smaller than that in faculae (˜ 1.3 kG) and a non‐flare active region (˜ 1.4kG). On the other hand, in a more power 2b‐flare the value of B was in the range from. 1.1 kG (the start of the flare) to 1.55kG. (during the peak). Thus the values of the field strength of flares somewhat differ from those both of faculae and active regions. The magnetic filling factor is approximately equal in flares (0.2‐0.40) and active regions (0.3) but several times larger as compared with faculae.
Diurnal variations of cosmic rays during a solar magnetic cycle
Authors: El‐Borie M. A. , Sabbah I. S. , Bishara A. A.
Published: July 2007

We have used data from five neutron monitor stations with primary rigidity (Rm) ranging from 16 GeV to 33 GeV to study the diurnal variations of cosmic rays over the period: 1965–1986 covering one 22‐year solar magnetic cycle. The heliosphere interplanetary magnetic field (IMF) and plasma hourly measurements taken near Earth orbit, by a variety of spacecraft, are also used to compare with the results of solar diurnal variation. The local time of maximum of solar diurnal diurnal variations displays a 22‐year cycle due to the solar polar magnetic field polarities. In general, the annual mean of solar diurnal amplitudes, magnitude of IMF and plasma parameters are found to show separte solar cycle variations. Moreover, during the declining period of the twenty and twenty‐ne solar cycles, large solar diurnal amplitudes are observed which associated with high values of solar wind speed, plasma temperature and interplanetary magnetic field magnitude B3.
Seasonal oscillations in length‐of‐day
Authors: Höpfner J.
Published: July 2007

Variations of annual and semiannual oscillations in rotation parameters have been investigated on the basis of length‐f‐ay(LOD) as well as atmospheric‐ngular‐omemtum (AAM) series. These oscillations were determined using band‐ass filters. In order to show the character of variations of seaasonal oscillations, amplitudes, phases and periods were computed by a least‐quares adjustment with the method of modified harmonic analysis at quarterly intervals. In addition, the seasonal imbalances in LOD and AAM budgets were determined and analysed in a similar way. These discrepancies were corrected for tidally excited effects. The non‐tmospheric oscillations without the annual tide effect Sa and the semiannual tide effect Ssa have variable amplitudes between 0.02 and 0.10 msec.
Multi‐colour surface photometry of a sample of HI‐detected late type galaxies
Authors: Vennik J. , Richter G. M. , Thänert W. , Biering C.
Published: July 2007

We perform BV RI surface photometry of 27 late type spiral and dwarf galaxies. All but two galaxies are selected from the HI‐survey of Schneider et al. (1990). We derive integral photometric parameters and the radial light and colour profiles and compare them to those of several LSB and bright field galaxy samples. Our new data confirm the earlier suggestions that the ‘ Schneider's sample’ consists of two different types of galaxies, with probably different star formation histories. First, the nearby (v0 ⩽ 1600 km s‐ 1) galaxies are mostly true dwarfs with the mean absolute magnitude of MB = ‐ 14.9±1.5 and with disk scale lengthes smaller than 1 kpc. These dwarfs are reasonably blue with median B – V = 0.49 and contain a large amount of neutral gas. Second, the distant (v0 ⩾ 4500 km s‐ 1) galaxies are late type LSB galaxies with typical face‐on disk central surface brightnesses of about 23.3 B‐ mag arcsec‐ 2 and ‘ normal’ disk scale lengthes of 3.6±1.5 kpc. Observed LSB galaxies are significantly redder, with median B – V ⋍ 0.72, than are the typical field LSB galaxies. The observed LSB galaxies are rich in HI but the current star formation activity is probably low.
An alternative method of finding bifurcation points in pseudo‐barotropes
Authors: Caimmi R.
Published: July 2007

Starting from the equations of hydrodynamics, which include both collisional and collisionless ideal fluids, the special case of pseudo‐arotropes with anisotropic pressure distribution along tangential or vertical direction (in respect to a “vertical” rotation axis) is considered. We find that vertical motions are equivalent to an imaginary rotation, and call “pseudo‐otation” the combination of rotation and real or imaginary peculiar circular motions. By use of a necessary condition for equilibrium, i.e. the coincidence of the boundary with an isopotential (gravitational + rotational centrifugal + real peculiar or imaginary peculiar centrifugal) surface, a new method of finding bifurcation points from axisymmetric to triaxial pseudo‐arotropic sequences – discussed in an earlier paper – is dealt with for the systems under discussion. A simple application to the special case where the isopycnic surfaces are spheroidal discloses that, on one hand, steadily pseudo‐otating, heterogeneous spheroids, cannot be equilibrium configurations and, on the other hand, the same results obtained by use of the virial technique hold when the current method can work. Then the coincidence of the boundary with an isopotential surface and the validity of the virial equations of the second order make two independent (necessary) conditions for equilibrium and both must be satisfied. Under the further assumptions of steady rotation and homeoidally or focaloidally striated distribution of matter, the configurations for which a bifurcation point must necessarily occurr, are determined. In the former alternative a connection is also established, between local (on the boundary) and global anisotropy of pressure distribution; in particular, it is found that local isotropy (on the boundary) involves global isotropy and vice versa. In both cases, the right amount of of anisotropy turns out to yield violation of a treshold for stability, ϵrot = −Erot/Epot ⩽ 0.14, conjectured by Ostriker and Peebles (1973). This result gives additional support to a conclusion established in an earlier paper: it seems more germane to speak about Ostriker‐eebles conjecture for stability in connection with visible bodies of galaxies, instead of Ostriker‐eebles criterion for stability in connection with self‐ravitating fluids.
On the emptiness of voids
Authors: Schmidt K.‐H. , Böhm P. , Elsässer H.
Published: July 2007

The observability of a galaxy population inside of voids is estimated by assuming a void population similar to the one of nearby field galaxies in density as well as in morphological mixture. Obviously an extension to apparent magnitudes beyond m = 22 for a complete sample of galaxies in a sufficient large field is needed to get reliable information on a void population.
Preliminary results on the study of the environment of a complete sample of Seyfert galaxies
Authors: Salvato M. , Rafanelli P.
Published: July 2007

The results of the study of the environment of a complete sample of Seyfert galaxies taken from the CfA Redshift Survey (Davis et al. 1983; Huchra et al. 1983) are shown. In particular we compare the distribution of the positions of all galaxies located within five diameters from each Seyfert galaxy of our sample with the angalogous distribution observed in a control sample of normal galaxies taken from the Merged Catalogue of Galaxies (hereafter MERCG) (Kogoshvili 1986). This research is based on the analysis of the digitized images of the “Digitized Sky Survey” and on the on‐line catalogues APM (Automatic Plate Measuring System) and APS (Automated Plate Scanner).
Micrometer measurements of visual double stars made at the Cǒte D'Azur Observatory
Authors: Ling J. F. , Prieto C.
Published: July 2007

We present 196 micrometer measurements of 99 double stars observed with the 50 and 74 cm refractor at the Cǒte D'Azur Observatory (Nice, France).
X‐ray variability study of ROSAT sources
Authors: Voges W. , Boller T.
Published: July 2007

The Röntgensatellite ROSAT has been in orbit since June 1,1990. After a 6‐month all‐sky survey ˜ 6,500 pointed observations have been performed. In total more than 150,000 X‐ray sources have been detected. Among the various object classes observed are comets, stars, white dwarfs, cataclysmic variables, neutron stars, black hole candidates, supernova remnants, nearby galaxies, AGN, and clusters of galaxies. Many of these objects are known to be time variable sources. Various catalogues of sources found in the ROSAT All‐Sky Survey and in the pointed observations are used as the basis for studying the temporal behaviour of ROSAT sources. This paper deals with the description, production and content of the various ROSAT catalogues with particular emphasis on the usefulness for the study of source variability.
Ultrasoft narrow‐line Seyfert 1 galaxies and X‐ray surveys
Authors: Brandt N. , Boller T.
Published: July 2007

We describe how recent X‐ray surveys have led to advances in the understanding of ultrasoft narrow‐line Seyfert 1 galaxies. The number of known ultrasoft narrow‐line Seyfert 1s has increased greatly in recent years due to X‐ray surveys, and it is now possible to obtain high quality 0.1–10 keV spectral and variability measurements for a large number of these galaxies. We generalize some of the correlations between X‐ray properties and optical emission line properties, focusing on how the ROSAT band spectral slope appears to be directly connected to the Boroson & Green (1992) primary eigenvector. We discuss how ultrasoft narrow‐line Seyfert 1s may well have extremal values of a primary physical parameter, and we describe new projects that should further improve our understanding of these extreme representatives of Seyfert activity.
Faint galaxies and the X‐ray background
Authors: Almaini O. , Shanks T. , Gunn K. F. , Boyle B. J. , Georgantopoulos I. , Griffiths R. E. , Stewart G. C. , Blair A. J.
Published: July 2007

We summarise our recent work on the faint galaxy contribution to the cosmic X‐ray background (XRB). At bright X‐ray fluxes (in the ROSAT pass band), broad line QSOs dominate the X‐ray source population, but at fainter fluxes there is evidence for a significant contribution from emission‐line galaxies. Here we present statistical evidence that these galaxies can account for a large fraction of the XRB. We also demonstrate that these galaxies have significantly harder X‐ray spectra than QSOs in the ROSAT band. Finally we present preliminary findings from infra‐red spectroscopy on the nature of this X‐ray emitting galaxy population. We conclude that a hybrid explanation consisting of obscured/Type 2 AGN surrounded by starburst activity can explain the properties of these galaxies and perhaps the origin of the entire XRB.
The X‐ray evolution of clusters of galaxies
Authors: Jones L. R. , Scharf C. , Perlman E. , Ebeling H. , Horner D. , Wegner G. , Malkan M. , Mchardy I.
Published: July 2007

The WARPS survey currently contains 48 X‐ray selected clusters and groups of galaxies, detected serendipitously in ROSAT PSPC archival pointed observations. The survey includes the highest redshift X‐ray selected cluster known (z=0.8325). The redshift range is large enough for evolutionary effects to be studied within the sample. Here we describe the X‐ray luminosity function and Log(N)‐Log(S) results for the initial complete sample of 29 spectroscopically confirmed clusters. We find that the X‐ray luminosity function does not evolve at z∽0.5 for cluster luminosities of ∽1044 erg s−1, but that there is a hint of positive evolution at lower luminosities from the number of groups & clusters found in the faintest available X‐ray cluster sample (the UK deep survey).
New ROSAT PSPC all‐sky survey maps of the diffuse soft X‐ray background
Authors: Freyberg M. J.
Published: July 2007

New maps of the soft X‐ray background (SXRB) using data from the ROSAT PSPC All‐Sky Survey have been constructed in 7 energy bands and with 12′ spatial resolution. Statistics of the intensity maps and of the exposure map are presented. Modeling of the 1/4 keV and of 3/4 keV data yields apparently conflicting results. However, besides the different data sets involved in the fits also different distances and regions may have been sampled with different properties (lower halo, upper halo of the Galaxy). Also model imperfections (e.g., temperature variations, non‐equilibrium) could explain some differences. An outlook is given to improved spectral binning of reprocessed (so‐called RASS2) survey data.
The XMM Serendipitous Survey
Authors: Watson M. G.
Published: July 2007

This paper provides an overview of the capabilities of the XMM Observatory and summarises the scope and potential of the XMM serendipitous survey. The role of the Survey Science Centre (SSC) in the XMM project is outlined, and a description is given of the SSC's plans for a follow‐up and identification programme which aims to ensure that the scientific potential of the serendipitous content of XMM fields can be fully exploited by the astronomical community.
Astronomical refraction and airmass
Authors: Kahl Kristensen L.
Published: July 2007

Standard astronomical refraction is approximated to ±1/2″ by a simple procedure valid to the horizon. In the approximation where absroption and refraction are proportional to the density of the air the computations of refraction and airmass should not be separated.
Disila‐Okoumal: A Silicon Analogue of the Ambergris Odorant Okoumal
Authors: Büttner Matthias W. , Burschka Christian , Junold Konstantin , Kraft Philip , Tacke Reinhold
Published: July 2007

Two‐fold sila‐substitution (C/Si exchange) in the saturated ring of the tetrahydronaphthalene skeleton of the ambery odorant okoumal (5) provides disila‐okoumal (6). The okoumal isomers 5 a–d were synthesized from 1‐(5,5,8,8‐tetramethyl‐5,6,7,8‐tetrahydro‐2‐naphthyl)ethanone (7), and the silicon analogues 6 a–d were synthesized from 1‐(5,5,8,8‐tetramethyl‐5,8‐disila‐5,6,7,8‐tetrahydro‐2‐naphthyl)ethanone (8). Detailed olfactory properties of 5 a–d and 6 a–d are reported, together with the respective threshold values. All enantiomers of okoumal and disila‐okoumal exhibit typical ambery odor notes with woody facets, as is characteristic of okoumal and karanal, but a stereocenter at the 2‐position was found to be of utmost importance for the odor thresholds; the lowest value of 0.31 ng per L air was measured for the 2R‐configured silicon compounds 6 a and 6 c.
Lateral wall protein content mediates alterations in cochlear outer hair cell mechanics before and after hearing onset
Authors: Jensen‐Smith Heather , Hallworth Richard
Published: July 2007

Specialized outer hair cells (OHCs) housed within the mammalian cochlea exhibit active, nonlinear, mechanical responses to auditory stimulation termed electromotility. The extraordinary frequency resolution capacity of the cochlea requires an exquisitely equilibrated mechanical system of sensory and supporting cells. OHC electromotile length change, stiffness, and force generation are responsible for a 100‐fold increase in hearing sensitivity by augmenting vibrational input to non‐motile sensory inner hair cells. Characterization of OHC mechanics is crucial for understanding and ultimately preventing permanent functional deficits due to overstimulation or as a consequence of various cochlear pathologies. The OHCs' major structural assembly is a highly‐specialized lateral wall. The lateral wall consists of three structures; a plasma membrane highly‐enriched with the motor‐protein prestin, an actin‐spectrin cortical lattice, and one or more layers of subsurface cisternae. Technical difficulties in independently manipulating each lateral wall constituent have constrained previous attempts to analyze the determinants of OHCs' mechanical properties. Temporal separations in the accumulation of each lateral wall constituent during postnatal development permit associations between lateral wall structure and OHC mechanics. We compared developing and adult gerbil OHC axial stiffness using calibrated glass fibers. Alterations in each lateral wall component and OHC stiffness were correlated as a function of age. Reduced F‐actin labeling was correlated with reduced OHC stiffness before hearing onset. Prestin incorporation into the PM was correlated with increased OHC stiffness at hearing onset. Our data indicate lateral wall F‐actin and prestin are the primary determinants of OHC mechanical properties before and after hearing onset, respectively. Cell Motil. Cytoskeleton 2007. © 2007 Wiley‐Liss, Inc.
Simultaneous orientation and cellular force measurements in adult cardiac myocytes using three‐dimensional polymeric microstructures
Authors: Zhao Yi , Lim Chee Chew , Sawyer Douglas Brian , Liao Ronglih , Zhang Xin
Published: July 2007

A number of techniques have been developed to monitor contractile function in isolated cardiac myocytes. While invaluable observations have been gained from these methodologies in understanding the contractile processes of the heart, they are invariably limited by their in vitro conditions. The present challenge is to develop innovative assays to mimic the in vivo milieu so as to allow a more physiological assessment of cardiac myocyte contractile forces. Here we demonstrate the use of a silicone elastomer, poly(dimethylsiloxane) (PDMS), to simultaneously orient adult cardiac myocytes in primary culture and measure the cellular forces in a three‐dimensional substrate. The realignment of adult cardiac myocytes in long‐term culture (7 days) was achieved due to directional reassembly of the myofibrils along the parallel polymeric sidewalls. The cellular mechanical forces were recorded in situ by observing the deformation of the micropillars embedded in the substrate. By coupling the cellular mechanical force measurements with on‐chip cell orientation, this novel assay is expected to provide a means of a more physiological assessment of single cardiac myocyte contractile function and may facilitate the future development of in vitro assembled functional cardiac tissue. Cell Motil. Cytoskeleton 2007. © 2007 Wiley‐Liss, Inc.
Synthesis and Biological Evaluation of Phosphate Prodrugs of 4‐Phospho‐D ‐erythronohydroxamic Acid, an Inhibitor of 6‐Phosphogluconate Dehydrogenase
Authors: Ruda Gian Filippo , Alibu Vincent P. , Mitsos Christos , Bidet Olivier , Kaiser Marcel , Brun Reto , Barrett Michael P. , Gilbert Ian H.
Published: July 2007

We have previously reported the discovery of potent and selective inhibitors of 6‐phosphogluconate dehydrogenase, the third enzyme of the phosphate pentose pathway, from Trypanosoma brucei, the causative organism of human African trypanosomiasis. These inhibitors were charged phosphate derivatives with restricted capacity to enter cells. Herein, we report the synthesis of five different classes of prodrugs: phosphoramidate; bis‐S‐acyl thioethyl esters (bis‐SATE); bis‐pivaloxymethyl (bis‐POM); CycloSaligenyl; and phenyl, S‐acyl thioethyl mixed phosphate esters (mix‐SATE). Prodrugs were studied for stability and activity against the intact parasites. Most prodrugs caused inhibition of the growth of the parasites. The activity of the prodrugs against the parasites appeared to be related to their stability in aqueous buffer.
Ultrafast 2D–IR Spectroscopy of Transient Species
Authors: Bredenbeck Jens , Helbing Jan , Kolano Christoph , Hamm Peter
Published: July 2007

Multidimensional spectroscopic experiments offer fascinating insights into molecular structure and dynamics in the field of NMR spectroscopy. With the introduction of ultrafast two‐dimensional infrared spectroscopy (2D–IR), multidimensional concepts have entered the optical domain, measuring couplings and correlations between molecular vibrations with femtosecond time resolution. In the transient 2D–IR (T2D–IR) experiments described in this minireview we exploit the high time resolution of 2D–IR to study transient species during fast nonequilibrium processes in real time. Information on molecular structure and dynamics is obtained that is not available from one‐dimensional spectroscopy. We discuss examples from chemistry, physics and biophysics.
Self‐Assembled Organic Nanostructures: Effect of Substituents on the Morphology
Authors: Su Wei , Zhang Yuexing , Zhao Chuntao , Li Xiyou , Jiang Jianzhuang
Published: July 2007

Three perylene‐3,4;9,10‐tetracarboxydiimide (PTCDI) compounds with two dodecyloxy or thiododecyl chains attached at the bay positions of the perylene ring, PTCDIs 1–3, were fabricated into nanoassemblies by a solution injection method. The morphologies of these self‐assembled nanostructures were determined by transmission electronic microscopy (TEM), scanning electronic microscopy (SEM), and atomic force microscopy (AFM). PTCDI compound 1, with two dodecyloxy groups, forms long, flexible nanowires with an aspect ratio of over 200, while analogue 3, with two thiododecyl groups, self‐assembles into spherical particles. In line with these results, PTCDI 2, with one dodecyloxy group and one thiododecyl group, forms nanorods with an aspect ratio of around 20. Electronic absorption and fluorescence spectroscopy results reveal the formation of H‐aggregates in the nanostructures of these PTCDI compounds owing to the π–π interaction between the substituted perylene molecules and also suggest a decreasing π–π interaction in the order 1>2>3, which corresponds well with the morphology of the corresponding nanoassemblies. On the basis of DFT calculations, the effect of different substituents at the bay positions of the perylene ring on the π–π interaction between substituted perylene molecules and the morphology of self‐assembled nanostructures is rationalized by the differing degree of twisting of the conjugated perylene system caused by the different substituents and the different bending of the alkoxy and thioalkyl groups with respect to the plane of the naphthalene.
Dielectric and thermal behaviour of holmium tartrate trihydrate crystals
Authors: Want B. , Ahmad F. , Kotru P. N.
Published: July 2007

Measurements on dielectric constant of holmium tartrate trihydrate crystals at frequencies of the applied a.c. in the range 1 kHz to 1 MHz and at temperature in the range 30°C to 330°C are reported. The dielectric constant ε′ increases with temperature at all frequencies, attains a peak near 250°C, and then decreases as the temperature goes beyond 250°C. The anomalous dielectric behaviour at near about 250°C is attributed to be as a result of crystallographic/polymorphic phase transition brought about in the material. The results on the dielectric behaviour of the material are supplemented by results of thermal analysis viz., TG and DTA. Thermogravimetric and differential thermal analytic techniques have been used to study thermal behaviour of the material. It is shown that the material is thermally stable up to 220°C beyond which it decomposes through three stages till the formation of holmium oxide at 1200°C. The non‐isothermal kinetic parameters e.g., activation energy and the frequency factor have been evaluated for first two stages of thermal decomposition by using the integral method of Coats and Redfern. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
International research collaboration: Building teams and managing conflicts
Authors: Bagshaw Dale , Lepp Margret , Zorn CeCelia R.
Published: July 2007

International research collaboration is a crucial, complex, and fragile process; effective strategies are needed to manage the inevitable conflicts that arise. Valuing diversity and developing cooperative goals, engaging in self‐reflection and reflexivity, promoting collaborative dialogue, taking time, and developing trust are discussed as strategies to support a fuller international engagement..
Zur theoretischen Begründung des „Minimumprinzips”︁ für die Spannung einer Gasentladung und einige weitere Folgerungen
Authors: Steenbeck Max
Published: July 2007

Ein „stationärer”︁ Vorgang kann durch eine Differentialgleichung mit einer zur Lösung an sich ausreichenden Anzahl von Randbedingungen beschreibbar sein, ohne daß dieser Vorgang sich tatsächlich so abspielt, wie es die Rechnung ergibt. Es können nämlich zum Teil Randbedingungen vorliegen, welche die Stationaritätsbilanz (von Energie, Teilchenzahl usw.) nur sehr schwach beeinflussen. Auch eine Verletzung solcher Bedingungen macht zwar grundsätzlich den Vorgang nichtstationär, doch können die damit verbundenen Schwankungen bei Verletzung von nur genügend schwach wirksamen Stationaritätsbedingungen kleiner sein, als die ohnehin praktisch oder prinzipiell vorhandenen Schwankungen jeder „echt”︁ stationären Größe; dann ist ein solcher „quasistationärer”︁ Vorgang von einem echt stationären Vorgang nicht mehr unterscheidbar. Ein quasistationärer Vorgang kann erheblich von der sich unter Berücksichtigung aller Randbedingungen ergebenden Lösung der Differential‐gleichung abweichen; er stellt sich dann ein, wenn er gegenüber Störungen stabiler ist als die echt stationäre Form, die dann überhaupt nicht auftritt. Der sich tatsächlich abspielende Vorgang wird dann durch ein Stabilitätskriterium bestimmt, das nicht aus der Differential‐gleichung für den stationären Zustand folgt, sondern zusätzlich eingeführt werden muß, und zwar unter Verletzung mindestens einer ausreichend schwach wirksamen Randbedingung.

Aus dieser Tatsache folgt u. a. die theoretische Berechtigung für die Anwendung des Minimumprinzips für die Brennspannung einer Bogenentladung, wobei die Idealisierung des Bogens im Kanalmodell eine Vereinfachung der Wirklichkeit bedeutet, die mit dem Minimumprinzip selbst nichts zu tun hat.
Die Berechnung von Energieverteilungen relativistischer Elektronen aus ihrer Synchrotronstrahlung. Anwendungen auf den Krebsnebel
Authors: Jäger J. , Wallis G.
Published: July 2007

Besides the general formula for the intensity of synchrotron radiation which is however not suitable for explicite calculations there exist a number of approximations valuable in certain frequency and energy regions. These approximative formulas together with a new approximation for relativistic electrons are discussed. It is shown how they fit to solve an integral equation for the energy distribution of the radiant electrons if the frequency distribution of their synchrotron radiation is given. In some cases our new approximation leads to a solution by Laplace transformation. This turns out convenient especially when investigating discrete cosmic radio sources. The received results are applicated to the optical and radio emission of the Crab Nebula. The influence of plasma on generating and propagating of synchrotron radiation is estimated.
Bestimmung der Kenndaten eines an die freie Atmosphäre austretenden Plasmastrahls
Authors: Neumann Werner
Published: July 2007

Es wird die Leistung, die der aus einem Plasmastrahlerzeuger austretende Argon‐Plasmastrahl als Wärme mit sich führt, als Funktion der elektrischen Leistung und der pro Zeiteinheit verbrauchten Menge des durch die Elektrodenöffnung strömenden Gases bestimmt. Ferner werden das Plasmavolumen, die effektive Plasmatemperatur, die maximale Temperatur und die Gesamtstrahlungsleistung des Plasmastrahls als Funktion der gleichen Parameter ermittelt.
Zustandsänderungen im isothermen Argon‐Plasma
Authors: Kümmel Ferdinand
Published: July 2007

Die nachfolgende Rechnung und das aus ihr entwickelte Diagramm befassen sich mit den möglichen thermodynamischen Zustandsänderungen eines strömenden Argon‐Plasmas in den Druck‐ und Temperaturbereichen 10 < p < 3 · 106 dyn/cm2 und 5000 < T < 26000 °K.
Zur Theorie laufender Schichten kleiner Amplitude in Niederdruckentladungen
Authors: Wojaczek Karl
Published: July 2007

Im Rahmen der linearisierten Theorie der nichtstationären positiven Säule der Niederdruckentladung werden Ausdrücke abgeleitet, mit deren Hilfe aus Meßdaten für das Dispersions‐ und Amplifikationsverhalten laufender Schichten auf Kenngrößen der Elementarprozesse im Plasma geschlossen werden kann. Zu diesen gehören die Ionenbeweglichkeit, die Wärmeleitfähigkeit der Elektronen sowie die Konzentrations‐ und Elektronentemperatur‐Abhängigkeit der Ionisations‐ und der Energieverlustrate. Außerdem liefert die Theorie für die Resonanzschichtweite bei der Grenzstromstärke einen Minimalwert, der nicht unterschritten werden darf.
Die positive Säule der Argon‐Niederdruckentladung im Übergangsbereich. II
Authors: Wojaczek Karl
Published: July 2007

Die im vorhergehenden Teil I der Arbeit mitgeteilten experimentellen Daten über laufende Schichten kleiner Amplitude im Puppschen Übergangsbereich werden zur Ermittlung von Kenndaten der in der positiven Säule vor sich gehenden Elementarprozesse ausgenutzt. Für die Ionenbeweglichkeit ergibt sich ein Wert, der gut mit der bekannten Beweglichkeit der Argon‐Atomionen übereinstimmt. Die Wärmeleitfähigkeit der Elektronen sowie die „effektive Ionisierungsspannung”︁ bleiben noch bis auf einen Faktor 2 unsicher. Die unerwartet starke Konzentrationsabhängigkeit der Ionisationsrate läßt darauf schließen, daß auch im Puppschen Übergangsbereich trotz relativ hoher Elektronenkonzentration noch merkliche Abweichungen von einer durchgängigen Maxwell‐Verteilung im Bereich großer Elektronengeschwindigkeiten vorliegen.
Zur Deutung der für die Schichtungsbildung in Argon bei höheren Entladungsstromstärken maßgeblichen Zeitparameter
Authors: Novák Miloš , Wojaczek Karl
Published: July 2007

Aus den Kenndaten für stationär angeregte laufende Schichten der Argon‐Entladung im Puppschenübergangsbereich wurden durch Kombination der Pekárekschen Theorie und der Dispersionstheorie der Schichtungswellen zwei für den jeweiligen Entladungszustand charakteristische Zeitkonstanten τ1 und τ2 bestimmt. Den Pekárekschen Ansätzen entsprechend wurden diese Zeitkonstanten als Ionenlebensdauer angeregte Atome, über die die Stufenionisation erfolgt, gedeutet. Im Rahmen dieser Interpretation läßt sich für die brennende Entladung ein Volumenrekombinationskoeffizient der Größenordnung 5 · 10−10 cm3s−1 ermitteln. Ferner sollte damit gerechnet werden, daß die Lebensdauer der maßgeblichen angeregten Atome unter den betrachteten Bedingungen im wesentlichen durch ionisierende Stöße bestimmt ist und die Konzentration der angeregten Atome in einem bestimmten Verhältnis zur Elektronenkonzentration steht.
Über die Einstellung gerichteter monoenergetischer Elektronen in die Maxwellverteilung der Plasmaelektronen einer Hg‐Niederdruckentladung
Authors: Behlke H. , Pupke H. , Jäger J.
Published: July 2007

Es wurde der Versuch unternommen, die Flugstrecke von Einschußelektronen in verschiedenen Plasmen zu bestimmen, die diese durchlaufen müssen, um sich ins Maxwellsche Gleichgewicht der Plasmaelektronen zu setzen.

Für bestimmte Fälle wurden 2 empirische Beziehungen gefunden, die den Zusammenhang zwischen diesen Strecken und den Plasmaparametern Ne (Elektronen dichte des Plasmas), Te (Elektronentemperatur), Ng (Neutralgasdichte), Upr (Voltgeschwindigkeit der eingeschossenen Primärelektronen) und Npr (Dichte der Primärelektronen) wiedergeben.

Die Einstellung der Einschußelektronen in die Maxwellverteilung wird diskutiert.
Zur nichtlinearen Theorie longitudinaler Elektronenschwingungen im Plasma
Authors: Leven Ronald
Published: July 2007

In der vorliegenden Arbeit wird die Verstärkung von Elektronenschwingungen beim Durchgang eines modulierten Elektronenstrahls durch ein Plasma in nichtlinearer Näherung betrachtet. Es wird gezeigt, daß man durch geeignete Wahl der wichtigsten Parameter wie Elektronenkonzentration, Strahlgeschwindigkeit, Temperatur, einen solchen Zustand des Systems hervorrufen kann, daß bereits eine geringfügige Vergrößerung der Elektronenkonzentration über einen kritischen Wert hinaus zur Verstärkung der Schwingungen führt, wobei das räumliche Anwachsen der Welle um so schwächer ist, je weniger sich die Elektronendichte von ihrem kritischen Wert unterscheidet. Daraus ergibt sich die Möglichkeit, die gesuchten Größen wie elektrische Feldstärke E und Verteilungsfunktion f sowie die Ableitungen der sich langsam ändernden Amplitude E0(x) und Phase Ψ(x) der Welle in Reihen nach einem kleinen Parameter zu entwickeln. Die Lösungsbedingungen für die Gleichungen der dritten Näherung liefern dann den räumlichen Verlauf von E0 und Ψ sowie der Energiedichte W des elektrischen Feldes und die stationären Werte Estat und Wstat für sehr große x.

Im letzten Abschnitt werden einige Zahlenbeispiele angeführt, die veranschaulichen, daß die Amplitude der Schwingungen des elektrischen Feldes und der Elektronenkonzentration mit der Energie des injizierten Elektronenstrahls wächst, wobei der Bestand an höheren Harmonischen um so geringer ist, je weniger die Elektronendichte den kritischen Wert übersteigt.

Die gemachten Voraussetzungen sind im wesentlichen: Eindimensionalität des Problems, Quasineutralität, Unbeweglichkeit der positiven Ionen, Vernachlässigung der Stöße.
Die dissipativen Tensoren des vollständig ionisierten Plasmas im starken Magnetfeld
Authors: Deutsch Rudolf V. , Gábos Zoltán
Published: July 2007

[Russian Text Ignored].
Das Temperaturfeld des Niederstrombogens in Luft
Authors: Kloss H. G. , Rademacher K.
Published: July 2007

Nach der Methode des Schwärzungsvergleichs mit einem Kohlebogen bekannter Temperaturverteilung wird das Temperaturfeld eines 10 A‐Kohlebogens ausgemessen. Ein Vergleich. der Temperaturprofile von Bögen zwischen Kohle‐ bzw. Metallelektroden zeigt, daß Elektrodenmaterialien mit Ionisierungsenergien über 7,5 eV im Rahmen der Meßgenauigkeit keinen Einfluß auf das Temperaturfeld des Bogens ausüben.
Die positive Argon‐Säule im weiten Rohr
Authors: Wojaczek Karl , Rademacher Karl , Rompe E. H. R.
Published: July 2007

Die in der homogenen positiven Säule der Argon‐Niederdruckentladung in weitem Rohr (R = 6 cm) aus Sondenmessungen ermittelten Elektronentemperaturen und Potentialgradienten lassen sich sowohl ihren absoluten Werten nach als auch bezüglich ihrer Abhängigkeit von der Entladungsstromstärke verstehen, wenn berücksichtigt wird, daß die elastischen und die unelastischen Elektronenstöße erhebliche Abweichungen von einer Maxwellschen Verteilung der Elektronengeschwindigkeiten im Bereich hoher Elektronenenergien bedingen.