bluuebunny/crossref_metadata_2025 huggingface dataset:
Superradiant terahertz Smith-Purcell radiation from surface plasmon excited by counterstreaming electron beams
Authors: Shin Young-Min , So Jin-Kyu , Jang Kyu-Ha , Won Jong-Hyo , Srivastava Anurag , Park Gun-Sik
Published: January 2007

The authors show that evanescent tunneling transmission of effective surface plasmon polaritons between two counterstreaming electron beams noticeably increases Smith-Purcell radiation (SPR) intensity by about two orders of magnitude as well as lower its transition threshold from a spontaneous emission to a stimulated one. An emission mechanism of the superradiant SPR is theoretically analyzed by the dielectric conversion of the structured metal surface and the boundary matching condition of Maxwell’s equations in comparison with numerical simulations.
Spectroscopy of vanadium (III) doped gallium lanthanum sulphide chalcogenide glass
Authors: Hughes M. , Rutt H. , Hewak D. , Curry R. J.
Published: January 2007

Vanadium doped gallium lanthanum sulphide glass (V:GLS) displays three absorption bands at 580, 730, and 1155nm identified by photoluminescence excitation measurements. Broad photoluminescence, with a full width at half maximum of ∼500nm, is observed peaking at 1500nm when exciting at 514, 808, and 1064nm. The fluorescence lifetime and quantum efficiency at 300K were measured to be 33.4μs and 4%, respectively. From the available spectroscopic data, the authors propose the vanadium ions’ valence to be 3+ and be in tetrahedral coordination. The results indicate a potential for the development of a laser or optical amplifier based on V:GLS.
Fano resonance in the luminescence spectra of donor bound excitons in polar semiconductors
Authors: Jin Kui-juan , Xu S. J.
Published: January 2007

An unusual response in the luminescence measurements of GaN thin film and ZnO bulk crystal is observed at low temperatures. The authors demonstrate theoretically that such an unusual response is due to the longitudinal optical phonon mediated Fano resonance involved in the recombination process of the donor bound exciton. The line shapes obtained by the calculation in the present mechanism are in excellent agreement with the experimental results.
Faster electro-optical response characteristics of a carbon-nanotube-nematic suspension
Authors: Chen Hui-Yu , Lee Wei , Clark Noel A.
Published: January 2007

The response times of rotational molecular orientation of neat and carbon-nanotube-doped nematic liquid crystals were acquired through the measurement of transient current induced by a direct-current step voltage and from optical transmission data. A model based on the dielectric displacement current was developed to describe the electric field dependence of the response and to yield a rotational viscosity that would decrease with increasing concentration of carbon nanotubes. Optical dynamic response also showed a reduced rotational viscosity, with the lightly doped cells exhibiting a faster relaxation process than that of the neat cell.
Tunable silicon-based light sources using erbium doped liquid crystals
Authors: Weiss S. M. , Zhang J. , Fauchet P. M. , Seregin V. V. , Coffer J. L.
Published: January 2007

Tunable emission in the near infrared is demonstrated on a silicon platform. The building blocks for the tunable light sources consist of porous silicon microcavities infiltrated with erbium doped nematic liquid crystals. Erbium ions are the luminescence source, porous silicon microcavities narrow the emission band, and liquid crystals enable tuning of the peak wavelength. Greater than 10dB attenuation is achievable by thermal actuation with microcavities having a Q factor of 200. The bandwidth of the tunable emission is limited by the liquid crystal birefringence.
Flow and species transport control in grooved microchannels using local electrokinetic forces
Authors: Hahm Jungyoon , Balasubramanian Ashwin , Beskok Ali
Published: January 2007

We present numerical simulation results for flow and species transport control in grooved microchannels using locally applied electric fields, and zeta potential patterned groove surfaces. The resulting mixed electro-osmotic/pressure-driven flow enables entrapment and release of prescribed amounts of scalar species in the grooves. The groove size and shape determine the volume of the entrapped species. Depending on the local electric field and zeta potential, each groove can simultaneously contain up to two species. This framework allows control over the interspecies diffusion and mixing using simple flow kinematics, and it is easily applicable for electrically neutral species. We envision utilization of this technique for combinatorial chemistry experiments in a microchannel with multiple grooves, where each groove can be addressed (filled, emptied, or mixed) independently. Alternatively, the technique can be used for electronic cooling, where the grooves increase heat transfer surface area without the adverse effects of recirculating flow pattern.
Simulation of an inhomogeneous elastic filament falling in a flowing viscous fluid
Authors: Zhu Luoding
Published: January 2007

We simulated the freely falling motion of an inhomogeneous flexible filament immersed in an incompressible viscous fluid under the action of gravity by the immersed boundary method. Our simulations show that the falling motion of an inhomogeneous filament is stable with respect to disturbances of small magnitude irrespective of the mass and bending modulus distributions. However, sufficiently large disturbances may bring the filament motion into a significantly different state: the filament deforms, rotates, and drifts towards one of the side boundaries while falling in the flowing fluid under the action of gravity. In addition our results indicate unstable filament motion depends more strongly on the bending modulus than the mass density. Our simulations also show the existence of two similar states for a homogeneous filament. The motions of inhomogeneous and homogeneous filaments are compared, and both quantitative and qualitative differences in the unstable motions are found. This is a starting point to understand the role of inhomogeneous filament properties in deciding its motion.
Early accumulation of non-enzymatically synthesised oxylipins in Arabidopsis thaliana after infection with Pseudomonas syringae
Authors: Grun Christoph , Berger Susanne , Matthes Daniel , Mueller Martin J.
Published: January 2007

The formation of non-enzymatic oxylipins is catalysed by reactive oxygen species. Reactive oxygen species are produced in response to pathogen attack. In this study, the accumulation of non-enzymatically formed hydroxy fatty acids and F1-phytoprostanes in leaves of Arabidopsis thaliana (L.) Heyhn upon infection with Pseudomonas syringae was investigated and compared with the accumulation of the enzymatically formed oxylipins jasmonic acid and 12-oxo-phytodienoic acid. Levels of all oxylipins increased after infection with a virulent and with an avirulent strain of P. syringae. Inoculation of the avirulent strain resulted in a biphasic accumulation with a first maximum around 5 h which was missing after inoculation of the virulent strain. Levels of free and esterified hydroxy fatty acids and F1-phytoprostanes increased after pathogen treatment; however, esterified compounds were 30 times more abundant than free oxylipins. The increase of the free compounds occurred later than the increase of the esterified compounds suggesting that non-enzymatic lipid oxidation occurs predominantly in membranes from which oxidised lipids can be released.
Phosphorus deficiency inhibits growth in parallel with photosynthesis in a C3 (Panicum laxum) but not two C4 (P. coloratum and Cenchrus ciliaris) grasses
Authors: Ghannoum Oula , Conroy Jann P.
Published: January 2007

This study compared the growth and photosynthetic responses of one C3 (Panicum laxum L.) and two C4 grasses (Panicum coloratum L. and Cenchrus ciliaris L.) to changes in soil phosphorus (P) nutrition. Plants were grown in potted soil amended with six different concentrations of P. One week before harvest, leaf elongation and photosynthetic rates and the contents of carbohydrate, P and inorganic phosphate (Pi) were measured. Five weeks after germination, plants were harvested to estimate biomass accumulation. At each soil P supply, leaf P contents were lower in the C3 (0.6–2.6 mmol P m–2) than in the two C4 grasses (0.8–4.1 mmol P m–2), and Pi constituted ~40–65% of total leaf P. The P deficiency reduced leaf growth, tillering and plant dry mass to a similar extent in all three grasses. In contrast, P deficiency suppressed photosynthetic rates to a greater extent in the C3 (50%) than the C4 grasses (25%). The foliar contents of non-structural carbohydrates were affected only slightly by soil P supply in all three species. Leaf mass per area decreased at low P in the two C4 grasses only, and biomass partitioning changed little with soil P supply. The percentage changes in assimilation rates and plant dry mass were linearly related in the C3 but not the C4 plants. Thus, P deficiency reduced growth in parallel with reductions of photosynthesis in the C3 grass, and independently of photosynthesis in the two C4 grasses. We propose that this may be related to a greater Pi requirement of C4 relative to C3 photosynthesis. Photosynthetic P use efficiency was greater and increased more with P deficiency in the C4 relative to the C3 species. The opposite was observed for whole-plant P-use efficiency. Hence, the greater P-use efficiency of C4 photosynthesis was not transferred to the whole-plant level, mainly as a result of the larger and constant leaf P fraction in the two C4 grasses.
Antibody to human leukocyte antigen triggers endothelial exocytosis
Authors: Yamakuchi Munekazu , Kirkiles-Smith Nancy C. , Ferlito Marcella , Cameron Scott J. , Bao Clare , Fox-Talbot Karen , Wasowska Barbara A. , Baldwin William M. , Pober Jordan S. , Lowenstein Charles J.
Published: January 2007

Although antibodies to HLA play a role in the pathogenesis of diseases processes such as rejection of transplanted organs, the precise mechanisms by which antibodies cause tissue injury are not completely understood. We hypothesized that antibodies to host tissues cause inflammation in part by activating endothelial exocytosis of granules that contain prothrombotic mediators such as von Willebrand Factor (VWF) and proinflammatory mediators such as P-selectin. To test this hypothesis, we treated human endothelial cells with murine monoclonal antibody W6/32 to HLA class I and then measured exocytosis by the release of VWF and the externalization of P-selectin. Antibody to HLA activates endothelial exocytosis in a dose-dependent manner over time. The biologically active complement split product, C5a, adds a slight but significant increase to antibody induction of exocytosis. Antibody to HLA alone or with C5a did not damage the cells. Cross-linking of HLA appears to play a role in the ability of antibody to activate exocytosis, because the W6/32 monovalent Fab fragment did not activate VWF release, but the bivalent F(ab′)
2
was effective in triggering exocytosis. To explore the
in vivo
effects of antibody upon graft injury, we infused W6/32 F(ab′)
2
antibody to human HLA into severe combined immunodeficient/beige mice that had been transplanted with human skin grafts. Antibody to HLA activated exocytosis and inflammation in human skin grafts. Our data show that antibody to host antigens can activate human endothelial cell exocytosis and leukocyte trafficking. By triggering vascular inflammation, antibody activation of exocytosis may play a role in transplant rejection.
Diagonals of normal operators with finite spectrum
Authors: Arveson William
Published: January 2007

Let
X
=

{λ
1
, …, λ
N
}

be a finite set of complex numbers, and let
A
be a normal operator with spectrum
X
that acts on a separable Hilbert space
H
. Relative to a fixed orthonormal basis

e
1
, e
2
, …

for
H, A
gives rise to a matrix whose diagonal is a sequence
d
= (

d
1
, d
2
, …

) with the property that each of its terms

d
n

belongs to the convex hull of
X
. Not all sequences with that property can arise as the diagonal of a normal operator with spectrum
X
. The case where
X
is a set of real numbers has received a great deal of attention over the years and is reasonably well (though incompletely) understood. In this work we take up the case in which
X
is the set of vertices of a convex polygon in ℂ. The critical sequences
d
turn out to be those that accumulate rapidly in
X
in the sense that

We show that there is an abelian group Γ

X

, a quotient of ℝ
2
by a countable subgroup with concrete arithmetic properties, and a surjective mapping of such sequences
d
↦
s(d)
∈ Γ

X

with the following property: If
s(d)
≠ 0, then
d
is not the diagonal of any such operator
A
. We also show that while this is the only obstruction when
N
=
2
, there are other (as yet unknown) obstructions when
N
=
3
.
Replication is required for the RecA localization response to DNA damage in
Bacillus subtilis
Authors: Simmons Lyle A. , Grossman Alan D. , Walker Graham C.
Published: January 2007

In both prokaryotes and eukaryotes, proteins involved in DNA repair often organize into multicomponent complexes that can be visualized as foci in living cells. We used a RecA-GFP fusion to examine the subcellular cues that direct RecA-GFP to assemble as foci in response to DNA damage. We used two different methods to inhibit initiation of DNA replication and determined that DNA replication is required for the cell to establish RecA-GFP foci after exposure to DNA-damaging agents. Furthermore, use of endonuclease cleavage to generate a site-specific double-strand break demonstrated that the replication machinery (replisome) and DNA synthesis are required for assembly of RecA-GFP foci during repair of a double-strand break. We monitored the cellular levels of RecA and found that focus formation does not require further induction of protein levels, suggesting that foci result from a redistribution of existing protein to sites of damage encountered by the replisome. Taken together, our results support the model that existing RecA protein is recruited to ssDNA generated by the replisome at sites of DNA damage. These results provide insight into the mechanisms that the cell uses to recruit repair proteins to damaged DNA in living cells.
Orphan nuclear receptor estrogen-related receptor α is essential for adaptive thermogenesis
Authors: Villena Josep A. , Hock M. Benjamin , Chang William Y. , Barcas Joanalyn E. , Giguère Vincent , Kralli Anastasia
Published: January 2007

Survival of organisms requires the ability to adapt to changes in the environment. Adaptation of oxidative metabolism is essential for meeting increased energy demands in response to stressors, such as exposure to cold temperatures or increased physical activity. Adaptive changes in metabolism are often achieved at the level of gene expression, and nuclear receptors have prevalent roles in mediating such responses. Estrogen-related receptor α (ERRα) was the first orphan nuclear receptor to be identified, and yet its physiologic function remains unknown. Here, we show that mice lacking ERRα are unable to maintain body temperature when exposed to cold. Surprisingly, the inability to adapt to cold is not due to defects in the acute transcriptional induction of genes important for thermogenesis. Rather, we show that ERRα is needed for the high levels of mitochondrial biogenesis and oxidative capacity characteristic of brown adipose tissue (BAT), and thus for providing the energy necessary for thermogenesis. ERRα fulfills this role by acting directly at genes important for mitochondrial function, parallel to other factors controlling mitochondrial gene expression, such as NRF1 and NRF2/GABPA. Our findings demonstrate that ERRα is a key regulator of mitochondrial biogenesis and oxidative metabolism, and essential for adaptive thermogenesis.
FSTL3 deletion reveals roles for TGF-β family ligands in glucose and fat homeostasis in adults
Authors: Mukherjee Abir , Sidis Yisrael , Mahan Amy , Raher Michael J. , Xia Yin , Rosen Evan D. , Bloch Kenneth D. , Thomas Melissa K. , Schneyer Alan L.
Published: January 2007

Activin and myostatin are related members of the TGF-β growth factor superfamily. FSTL3 (Follistatin-like 3) is an activin and myostatin antagonist whose physiological role in adults remains to be determined. We found that homozygous FSTL3 knockout adults developed a distinct group of metabolic phenotypes, including increased pancreatic islet number and size, β cell hyperplasia, decreased visceral fat mass, improved glucose tolerance, and enhanced insulin sensitivity, changes that might benefit obese, insulin-resistant patients. The mice also developed hepatic steatosis and mild hypertension but exhibited no alteration of muscle or body weight. This combination of phenotypes appears to arise from increased activin and myostatin bioactivity in specific tissues resulting from the absence of the FSTL3 antagonist. Thus, the enlarged islets and β cell number likely result from increased activin action. Reduced visceral fat is consistent with a role for increased myostatin action in regulating fat deposition, which, in turn, may be partly responsible for the enhanced glucose tolerance and insulin sensitivity. Our results demonstrate that FSTL3 regulation of activin and myostatin is critical for normal adult metabolic homeostasis, suggesting that pharmacological manipulation of FSTL3 activity might simultaneously reduce visceral adiposity, increase β cell mass, and improve insulin sensitivity.
Directional shear flow and Rho activation prevent the endothelial cell apoptosis induced by micropatterned anisotropic geometry
Authors: Wu Chia-Ching , Li Yi-Shuan , Haga Jason H. , Kaunas Roland , Chiu Jeng-Jiann , Su Fong-Chin , Usami Shunichi , Chien Shu
Published: January 2007

To study the roles of anisotropic cell morphology and directionality of mechanical force in apoptosis, the spreading of human umbilical vein endothelial cells (HUVECs) was constrained by growing on micropatterned (MP) strips of fibronectin (FN, 20 μg/cm
2
) with widths of 15, 30, and 60 μm on silicone membrane. Cells on 30- and 60-μm strips, like cells on a nonpatterned (NP) surface coated with FN, showed clear actin stress fibers with anchoring spots of phosphorylated focal adhesion kinase (
p
-FAK) and no significant apoptosis. On 15-μm strips, cells had few stress fibers, no
p
-FAK, and significant apoptosis. After seeding for 12 h, the cells were subjected to pulsatile shear stress (12 ± 4 dyn/cm
2
) parallel or perpendicular to MP strips, or kept under static condition. Parallel flow caused cell elongation with enhanced stress fibers and
p
-FAK, and a reduction in apoptosis, but perpendicular flow did not. The Rho inhibitory C3 exoenzyme abolished the effects of parallel flow. RhoV14, the constitutively active Rho, enhanced stress fibers and
p
-FAK, and prevented apoptosis of HUVECs on 15-μm strips under static condition. RhoV14 also reduced cell apoptosis under both parallel and perpendicular flows. Our results indicate that cell apoptosis can be modulated by changes in ECM micropatterning, anisotropic cell morphology, and mechanical forces. These extracellular microenvironment factors affect cell survival through alterations in Rho GTPase activity, stress fiber organization, and FAK phosphorylation.
Differences in protein mobility between pioneer versus follower growth cones
Authors: Kulkarni Rajan P. , Bak-Maier Magdalena , Fraser Scott E.
Published: January 2007

Navigating growth cones need to integrate, process and respond to guidance signals, requiring dynamic information transfer within and between different compartments. Studies have shown that, faced with different navigation challenges, growth cones display dynamic changes in growth kinetics and morphologies. However, it remains unknown whether these are paralleled by differences in their internal molecular dynamics. To examine whether there are protein mobility differences during guidance, we developed multiphoton fluorescence recovery after photobleaching methods to determine molecular diffusion rates in pathfinding growth cones
in vivo
. Actively navigating growth cones (leaders) have consistently longer recovery times than growth cones that are fasciculated and less actively navigating (followers). Pharmacological perturbations of the cytoskeleton point to actin as the primary modulator of diffusion in differently behaving growth cones. This approach provides a powerful means to quantify mobility of specific proteins in neurons
in vivo
and reveals that diffusion is important during axon navigation.
Low-dose
l
-arginine administration increases microperfusion of hindlimb muscle without affecting blood pressure in rats
Authors: Ohta Fumio , Takagi Tomo , Sato Hiroyuki , Ignarro Louis J.
Published: January 2007

The objective of this work was to evaluate the influence of exogenous
l
-arginine on the capillary blood flow of peripheral tissues of normotensive subjects. Rats were anesthetized with sodium pentobarbital, and the blood flow of femoral, dorsal, and ventral skin and gastrocnemius and soleus muscle was measured by laser Doppler flow and microsphere methods to compare the blood flow before and after the
l
-arginine infusion.
l
-Arginine lowered the mean blood pressure in a dose-dependent manner, but a statistically significant reduction in mean blood pressure was detected only at a high dose of 500 mg/kg of body weight. The significant blood flow increment was detected after the
l
-arginine infusion at doses of 50 and 150 mg/kg without causing hypotension. Nicardipine, a calcium channel blocker, also increased the skin blood flow, but the blood flow increment and blood pressure fall were comparable. A significant increment in microperfusion was detected in gastrocnemius, soleus muscle, and ventral skin compared with control group by the microsphere method. No adverse effects were observed during
l
-arginine and microsphere infusion. The present work indicates that
l
-arginine infusion increases muscle capillary blood flow in rats that are not performing exercise. Supplementation with
l
-arginine might provide additional blood flow at rest and during exercise and result in the improvement of muscle performance and exercise capacity.
DEC-205 receptor on dendritic cells mediates presentation of HIV gag protein to CD8
+
T cells in a spectrum of human MHC I haplotypes
Authors: Bozzacco Leonia , Trumpfheller Christine , Siegal Frederick P. , Mehandru Saurabh , Markowitz Martin , Carrington Mary , Nussenzweig Michel C. , Piperno Angela Granelli , Steinman Ralph M.
Published: January 2007

Optimal HIV vaccines should elicit CD8
+
T cells specific for HIV proteins presented on MHC class I products, because these T cells contribute to host resistance to viruses. We had previously found that the targeting of antigen to dendritic cells (DCs) in mice efficiently induces CD8
+
T cell responses. To extend this finding to humans, we introduced the HIV p24 gag protein into a mAb that targets DEC-205/CD205, an endocytic receptor of DCs. We then assessed cross-presentation, which is the processing of nonreplicating internalized antigen onto MHC class I for recognition by CD8
+
T cells. Low doses of αDEC-gag, but not control Ig-gag, stimulated proliferation and IFN-γ production by CD8
+
T cells isolated from the blood of HIV-infected donors. αCD205 fusion mAb was more effective for cross-presentation than αCD209/DC-SIGN, another abundant DC uptake receptor. Presentation was diverse, because we identified eight different gag peptides that were recognized via DEC-205 in 11 individuals studied consecutively. Our results, based on humans with highly polymorphic MHC products, reveal that DCs and DEC-205 can cross-present several different peptides from a single protein. Because of the consistency in eliciting CD8
+
T cell responses, these data support the testing of αDEC-205 fusion mAb as a protein-based vaccine.
Patients with hippocampal amnesia cannot imagine new experiences
Authors: Hassabis Demis , Kumaran Dharshan , Vann Seralynne D. , Maguire Eleanor A.
Published: January 2007

Amnesic patients have a well established deficit in remembering their past experiences. Surprisingly, however, the question as to whether such patients can imagine new experiences has not been formally addressed to our knowledge. We tested whether a group of amnesic patients with primary damage to the hippocampus bilaterally could construct new imagined experiences in response to short verbal cues that outlined a range of simple commonplace scenarios. Our results revealed that patients were markedly impaired relative to matched control subjects at imagining new experiences. Moreover, we identified a possible source for this deficit. The patients' imagined experiences lacked spatial coherence, consisting instead of fragmented images in the absence of a holistic representation of the environmental setting. The hippocampus, therefore, may make a critical contribution to the creation of new experiences by providing the spatial context into which the disparate elements of an experience can be bound. Given how closely imagined experiences match episodic memories, the absence of this function mediated by the hippocampus, may also fundamentally affect the ability to vividly re-experience the past.
Increased apoptosis, p53 up-regulation, and cerebellar neuronal degeneration in repair-deficient Cockayne syndrome mice
Authors: Laposa R. R. , Huang E. J. , Cleaver J. E.
Published: January 2007

Cockayne syndrome (CS) is a rare recessive childhood-onset neurodegenerative disease, characterized by a deficiency in the DNA repair pathway of transcription-coupled nucleotide excision repair. Mice with a targeted deletion of the CSB gene (
Csb
−/−
) exhibit a much milder ataxic phenotype than human patients.
Csb
−/−
mice that are also deficient in global genomic repair [
Csb
−/−
/
xeroderma pigmentosum C (Xpc)
−/−
] are more profoundly affected, exhibiting whole-body wasting, ataxia, and neural loss by postnatal day 21. Cerebellar granule cells demonstrated high TUNEL staining indicative of apoptosis. Purkinje cells, identified by the marker calbindin, were severely depleted and, although not TUNEL-positive, displayed strong immunoreactivity for p53, indicating cellular stress. A subset of animals heterozygous for
Csb
and
Xpc
deficiencies was more mildly affected, demonstrating ataxia and Purkinje cell loss at 3 months of age. Mouse,
Csb
−/−
, and
Xpc
−/−
embryonic fibroblasts each exhibited increased sensitivity to UV light, which generates bulky DNA damage that is a substrate for excision repair. Whereas
Csb
−/−
/
Xpc
−/−
fibroblasts were more UV-sensitive than either single knockout, double-heterozygote fibroblasts had normal UV sensitivity.
Csb
−/−
mice crossed with a strain defective in base excision repair (Ogg1) demonstrated no enhanced neurodegenerative phenotype. Complete deficiency in nucleotide excision repair therefore renders the brain profoundly sensitive to neurodegeneration in specific cell types of the cerebellum, possibly because of unrepaired endogenous DNA damage that is a substrate for nucleotide but not base excision repair.
Doubly-excited States in Three-electron Systems
Authors: Sten Lunell
Published: January 2007

Quantum mechanical calculations of the quartet states of the three-electron atoms are discussed with particular reference to the classification of the4Poand4Pestates. New assignments are proposed for the lines at 4 760 Å, 5 315 Å and 8 517 Å in Li I.
Lifetime Measurements in La II with the Beam-Laser Method
Authors: A Arnesen  , A Bengtsson  , R Hallin  , J Lindskog  , C Nordling  , T Noreland
Published: January 2007

Cascade-free lifetime measurements of they3F2 3 40, thez1D20and thez3D1 2 30levels in La II have been made with the beam-laser technique. Our results, together with other recent lifetime measurements in La II, are compared with lifetimes inferred from transition probabilities measured by Corliss and Bozman (CB). An energy-dependent correction factor to the CB lifetimes is found, indicating a misjudgement of the effective temperature in Corliss' and Bozman's arc. A new value of the La solar photosphere abundance based on six transitions in La II, is presented.
Oscillator Strengths for Some Mn II Lines and the Solar Mn Abundance
Authors: I Martinson  , L J Curtis  , P L Smith  , E Biémont
Published: January 2007

Oscillator strengths are given for transitions belonging to thea5S-z5P0anda5D-z5P0multiplets in Mn II. The data originate from beam-foil measurements of thez5P1,2,30level lifetimes and branching-ratio determinations. Theoreticalf-values are also given for these transitions, the agreement between experiment and theory being satisfactory. Using the experimentalgf-values obtained in this work and empirical solar models, the solar abundance of Mn has been determined to be logNMn= 5.4 ± 0.2 (on the logNH= 12.00 scale).
f-Values and Abundances of the Elements in the Sun and Stars
Authors: Emile Biémont  , Nicolas Grevesse
Published: January 2007

After a brief summary giving the reasons for which the elemental abundances are of considerable interest and the methods used to derive solar and stellar abundances, we shall essentially review the atomic and molecularf-values needed by solar spectroscopists, with a brief account of some problems encountered in stellar spectroscopy studies.
Measurements of Optical Lifetimes > 1 μ s Using Pulsed Electron Excitation Techniques
Authors: L J Curtis  , P Erman
Published: January 2007

A study has been made of possible effects which could distort decay curves of atomic and molecular levels with lifetimes > 1 μ s when measured using delayed coincidence techniques following pulsed excitation of a static gas cell. Measured decay curves are compared to calculational models, quantitative estimates are established in terms of experimental parameters, and methods for minimizing and correcting these distortions are discussed.
Lifetimes of Inner Shell Multiple Vacancy States in Argon
Authors: J Nordgren  , H Ågren  , L Selander  , C Nordling  , K Siegbahn
Published: January 2007

The lifetimes of L and LM vacancy states in argon have been determined from the natural widths of L X-ray emission lines in a high resolution experiment.
Binding Corrections and the Pion-Deuteron Scattering Length
Authors: Göran Fäldt
Published: January 2007

We study binding corrections in a pion-deuteron like system assuming S-wave separable potentials. In a Watson multiple scattering expansion (or Faddeev calculation) binding corrections of a given order appear in multiple scattering terms of different types. Individually, these corrections are quite large but taken together substantial cancellations occur. As a consequence the naive impulse approximation becomes very good. Analytic methods are used throughout.
Material-dependent Variations of Alignment in Beam-Foil Excitation
Authors: H G Berry  , G Gabrielse  , T Gay  , A E Livingston
Published: January 2007

We have measured the linear polarization fractions of the 2s1S-3p1PHe I transition at 5 016 Å excited by the passage of helium ions through thin perpendicular foils at beam energies of 40 to 220 keV. Metallic foils such as Au and Ag show less polarization than carbon, while non-conducting SiO2foils produce increased linear polarization. Time variations of the polarization show that the build-up of impurities on the final surface of the foils yields carbon-foil like polarizations. At higher beam energies of 0.6 to 1.0 MeV, all foils show increased polarization for neon transitions, but decreased polarization for He II transitions with respect to the carbon foil values.
KαhHypersatellite Spectra and K Shell Double Photoionization Cross Sections of Elemental Mg, V, Cr, Mn, and Fe
Authors: O Keski-Rahkonen  , J Saijonmaa  , M Suvanen  , A Servomaa
Published: January 2007

TheKαhhypersatellite spectra of Mg, V, Cr, Mn, and Fe are measured with a plane crystal Bragg spectrometer for the first time in photon excitation. The experimental energies of theKα2hlines are obtained and the energies of theKα1,2andKα1,2hlines are calculated using a multiconfiguration Dirac-Fock program of Desclaux. TheK-shell double photoionization cross sections are estimated from the experimental hypersatellite intensities. Results agree qualitatively with existing theoretical calculations based on the shake theory and correlated wave functions.
Analysis of the P VI Spectrum
Authors: M Eidelsberg  , M-C Artru
Published: January 2007

The spectrum of five-times ionized phosphorus (P VI) is observed in the 400-1 500 Å wavelength range. A total of 76 new lines are measured and classified as transitions between the 2p53s, 3p, 3dand 4fconfigurations. All energy levels in these configurations are determined. Their identification is supported by the results of parametric calculations and by an isoelectronic comparison.
Forced Radial Oscillations of a Fully Ionized Cylindrical Plasma Surrounded by a Partially Ionized Plasma Shell
Authors: M Bures  , E Tennfors
Published: January 2007

Forced radial magnetoacoustic oscillations of a fully ionized cylindrical plasma, surrounded by a partially ionized shell are excited by means of an external source. The radial plasma profiles of the macroscopic field quantities in the fully and partially ionized regions are obtained as functions of the degree of ionization, the temperature and the position of the boundary between the two regions. The absorbed power is calculated. The nonresonant as well as the resonant cases are treated. It is shown that the main part of the power is absorbed in the outer shell unles a suitable resonance is used to enhance the macroscopic field quantities in the fully ionized plasma part and the dimensions of the outer shell are kept small.
Density-dependent Lines of One- and Two-electron Ions in Diagnostics of Laboratory plasma. I. The rates of collision relaxation of excited levels
Authors: V P Shevelko  , I Yu Skobelev  , A V Vinogradov
Published: January 2007

Plasma devices with inertial plasma confinement such as laser produced plasmas, exploding wires, plasma focus, etc., which have been rapidly developed during recent years, appear to be very intensive sources of spectral line radiation in far UV and X-ray regions. Analysis of this radiation provides a good tool for plasma diagnostics with very high electron densities up to 1022cm-3. In this work, consisting of two parts, we consider the mechanism of the formation of spectral lines in hot and dense plasma. The key point for density diagnostics is the fact that for some ion levels the rate of collisional relaxation has the same order of magnitude as the radiative decay. Thus the intensities of spectral lines arising from these levels show a strong dependence on electron density which makes diagnostics possible.

In the first paper, emphasis is laid on the calculation of rates of transition between close ion levels induced by electron or ion impact, which usually gives the main contribution to the collisional relaxation constants. The influence of plasma polarization effects on the collision frequency in a dense plasma is also considered.

In a second paper, the formation of spectral lines of hydrogen-like, helium-like and oxygen-like ions will be considered for electron density 1018cm-3⩽N⩽ 1024cm-3and the ion charge 10 ⩽Z⩽ 19.
The Growth of Modulational Instability for Randomized Initial Conditions
Authors: J Weiland
Published: January 2007

The growth of the modulational instability has been studied in a one-dimensional configuration. In order to simulate a turbulent situation the phases of 31 Fourier components in space have been picked at random. Both stationary and moving solitons are obtained. Comparisons with the quasi-static approximation are made.
Evolution in Space and Time of two Interacting Intensities
Authors: Hans Wilhelmsson
Published: January 2007

The basic nonlinear coupled equations describing the interaction between two intensities (or two populations) are discussed. Analytic solutions are deduced for the evolution in space and time of initially given perturbations of the equilibrium intensities.
Electron Spectra of Free Metal Atoms
Authors: W Mehlhorn  , B Breuckmann  , D Hausamann
Published: January 2007

Core level energies of free metal atoms have been determined experimentally by means of photo-electron and Auger electron spectroscopy and are compared with theoretical and estimated "free atom" values. Theoretical values agree with our experimental energies within 1 eV whereas the estimated "free atom" values deviate from them by as much as 8 eV. The occurrence of strong correlation effects in the Auger spectra of the alkali-earth atoms is demonstrated at the 3d-Auger spectrum of Sr and 4d-Auger spectrum of Ba. Thesuper Coster-Kronig andCoster-Kronig transitions of free Zn atoms have been measured. From a quantitative analysis of these spectra, the level widths Γ(3p3/2) = Γ(3p1/2) have been determined and are compared with experimental solid state values and with theoretical ones.
Photoelectron Studies of Ionic Materials using Molecular Beam Techniques
Authors: A W Potts  , W C Price
Published: January 2007

Photoelectron spectra of the monomeric species of several classes of ionic molecule have been obtained by crossing a molecular beam of the material with a photon beam containing photons of energies up to 50 eV (He I and He II lines). In this way electrons from the s
2, p
6 and d
10 shells of the relevant atoms (or ions) were ejected and studied by photoelectron spectroscopy. The spectra are found to be explicable in terms of simple ionic models in which polarization of both negative and positive ions but mainly the former are taken into account. Work is reported on the alkali halides and the halides of Tl, In, Sn and Pb.
Vacuum Ultraviolet Photoelectron Spectroscopy of Transient Species: Part 8, the t-Butyl Radical
Authors: John Dyke  , Neville Jonathan  , Edmond Lee  , Alan Morris  , Marcus Winter
Published: January 2007

The vacuum ultraviolet photoelectron spectrum of the t-butyl radical produced by pyrolysis of 2,2' azoisobutane has been investigated. The band associated with the first ionization potential is the only one for which vibrational structure could be resolved and this has been analysed in terms of ionization of a vibrationally excited t-butyl molecule. From the observed Franck-Condon envelope of this band, it is concluded that the t-butyl radical has a pyramidal C3v
geometry in its ground electronic state and the barrier to inversion is estimated to be (900±100) cm-1 with an out-of-plane distance of the central carbon atom of (0.30±0.05) Å. The first vertical and adiabatic ionization potentials of the t-butyl radical are estimated to be (6.90±0.01) eV and (6.58±0.01) eV respectively. The higher ionization potential region is interpreted with the aid of semiempirical molecular orbital calculations.
Some Aspects of Acetylene Photoelectron Spectroscopy
Authors: G Bieri  , E Heilbronner  , T B Jones  , E Kloster-Jensen  , J P Maier
Published: January 2007

Recent work concerning the photoelectron spectra of unsubstituted and substituted acetylenes and polyacetylenes is reviewed. It is shown that these systems are ideal cases for the investigation of some of the principles which govern photoelectron spectra of organic compounds.
Study of K-LL Auger Processes for Light Elements above Z = 10
Authors: Thomas A Carlson  , W B Dress  , G L Nyberg
Published: January 2007

A comprehensive review is given of theK-LLAuger spectrum for members of the third row of the periodic table. This group contains the lightest elements wherein an Auger process can occur without the direct participation of the valence shell. Recent Auger spectra induced by x-ray photoionization on Mg, Al, and Si metals and their oxides are given as well as preliminary results on salts of Na and K, and for comparison, theL-MMspectra of RbCl. Our results have been combined with previous experimental data and theory in order to obtain an overview. Four topics concerned with Auger processes are discussed: Energies, relative intensities, chemical shifts, and satellite structure. Interlaced throughout the entire paper is a discussion of the role played by the chemical environment and electron correlation.
High Resolution Gas Phase Photoelectron Spectra of Core d Levels Using He II Radiation
Authors: G M Bancroft  , L L Coatsworth  , D K Creber  , J Tse
Published: January 2007

Using a newly constructed charged particle oscillator He II discharge lamp, we have obtained high resolution (⩽0.03 eV instrumental resolution) spectra of the outermost metal core d levels in alkyl compounds of Cd, In, and Pb. The Cd and In 4d spectra of Me2Cd (Me = CH3), Et2Cd (Et = C2H5) and Me3In are split into five peaks due to the combined effects of spin orbit splitting (5/2 λ) and an asymmetric crystal field (the C
2
0 term which transforms like the electric field gradient). As expected, the spin orbit split Pb 5d levels in the tetrahedral molecule Et4Pb (C
2
0 = 0) show no noticeable crystal field splitting. The new photoelectron effect enables electric field gradients to be obtained in the gas phase. Our derived C
2
0 values are consistent with previously measured nuclear electric field gradients in Cd and In compounds; and the measured C
2
0 value for Me2Cd is in qualitative agreement with that calculated by H. Basch from an ab initio self-consistent field (SCF) calculation. Because the measured linewidths are mainly due to the inherent natural linewidths of the d levels, we can readily obtain natural d widths from these spectra. The high resolution spectra of the Cd 4d levels of Et2Cd enable us to resolve Cd 4d peaks due to Cd atoms and EtCd· radicals. The Cd 4d spectra of Me2Cd and Et2Cd taken at 21.2 eV, 40.8 eV, and 51.0 eV photon energies show marked changes in the relative intensities of the five 4d peaks.
Autoionisation of NO by UV-Photoelectron Spectroscopy
Authors: P Natalis  , J Delwiche  , J E Collin  , G Caprace  , M Th Praet
Published: January 2007

The photoelectron spectrum of nitric monoxide NO has been studied with the 73.58 nm line of Ne I. Strong perturbation of theX1Σ+anda3Σ+bands is ascribed to autoionisation from a Rydberg state. The molecular characteristics of the R-state are discussed on the basis of selection rules, comparison between experimental vibrational progressions and Franck-Condon factors calculations, and a2Σ+symmetry is deduced. Electronic branching ratios are also examined.
Vibronic Interaction in Molecules and Ions. I. The first order Jahn-Teller interaction in doubly degenerate electronic states of C3ν type molecules
Authors: F T Chau  , L Karlsson
Published: January 2007

Expressions relevant to optical and electron spectroscopy are presented for calculation of the vibronic energy levels and Franck-Condon factors due to excitation of a Jahn-Teller active e vibrational mode in an electronic E state of C3v type molecules. Both A → E and E → A electronic transitions are investigated with allowance of different vibrational energies in the initial and final states. Energy levels and Franck-Condon factors including consideration of hot band transitions are explicitly given for some selected cases. Application is made to the fourth electron band at 18 eV of the electron spectrum of SO3. The vibronic band structure is well reproduced when the Jahn-Teller coupling parameters D
3 and D
4 of the ν3 and ν4 active modes are 0.06 and 0.35, respectively. A theoretical estimation is also made of the Jahn-Teller stabilization energy of SO3
+. Finally, the X → B Rydberg transition of CF3I is discussed and a value of 0.01 is suggested for the Jahn-Teller coupling parameter D
6.
Molecular Auger Electron Spectra of Second Row Elements. Sulfur Compounds
Authors: L Asplund  , P Kelfve  , B Blomster  , H Siegbahn  , K Siegbahn  , R L Lozes  , U I Wahlgren
Published: January 2007

High resolution KLL Auger electron spectra of H2S, SO2 and SF6 are presented and analyzed. The experimental equipment, using a recently designed electron retardation system, is described. For the analysis of the spectra, ab initio computations have been performed including configuration interaction. The discussion is mainly focussed on the satellite structure. The major satellites are due to shake-off in the valence shell accompanying the K-ionization and are found to be chemically dependent. Extra lines are also observed, which are assigned to autoionization processes.
Some Experimental and Theoretical Aspects of Structure, Bonding and Reactivity of Organic and Polymeric Systems as Revealed by ESCA
Authors: D T Clark
Published: January 2007

Recent theoretical and experimental developments in the ESCA research programme at Durham are reviewed. Detailed investigations reveal the structural dependence of sample charging phenomena which therefore forms an interesting extra information level for the technique. Direct measurements have been made of electron mean free paths as a function of kinetic energy in both linear and cross linked polymeric systems and these reveal a close similarity to typical metals and semi conductors. The large range of information levels available from the ESCA experiment allow the development of quantitative aspects of the surface science of polymeric systems. Theoretical work has been directed towards the investigation of various aspects of relaxation phenomena accompanying core ionization and data is presented on the enhancement of weak interactions in going to the core hole state manifold and in the study of vibrational fine structure for both direct photoionization and shake up states.
ESCA Studies of Ion Complexes Between a Crown-ether and Alkali Halides
Authors: Ove Bohman  , Per Ahlberg  , Nils Mårtensson  , Kai Siegbahn
Published: January 2007

ESCA has been used to study the complexation of the alkali cations Na+, K+ and Rb+ by the crown-ether, dibenzo-18-crown-6. The binding energies of cations as well as the counter ions (Cl-, Br- and I-), oxygens and carbons have been measured. The results reveal strong backbonding effects. A comparison of the electron binding energies for the complexed and uncomplexed alkali halides was also performed. The differences are discussed within the Born model for ionic solids and the hypothesis that the crownether complexes constitute a standard reference system for the comparison of electron binding energies in different alkali halides was tested.
The Use of Internal Standards for Measuring the ESCA Chemical Shift in Coordination Compounds of Cobalt
Authors: R Larsson  , B Folkesson
Published: January 2007

The binding energies of Co2p3/2, N1sand C1sand Cl2p3/2electrons have been measured for the compound Coen3(ClO4)3where en = ethylenediamine. The perchlorate ion has been used as an internal standard. The main theme of the paper is whether it is possible or not to use sub-standards that are related to a certain main standard. In the present case the latter is the tetraphenylphosphonium ion. As sub-standards K+, ClO4-and Cl-are tested. In this way the charge distribution is determined for the Coen33+and Co(CN)63-ions. The effective charges of cobalt are found to beqCo= +0.7±0.3 andqCo= +0.6±0.4, respectively.