bluuebunny/crossref_metadata_2025 huggingface dataset:
Structure of short polymers at interfaces: A combined simulation and theoretical study
Authors: Goel Teena , Patra Chandra N. , Ghosh Swapan K. , Mukherjee Tulsi
Published: August 2004

The structure of polymers confined between surfaces is studied using computer simulation and a density functional approach. The simple model system considers the polymer molecule as a pearl necklace of freely jointed hard spheres, having attractions among the beads, confined between attractive surfaces. This approach uses the universality of the free-energy functional to obtain the self-consistent field required in the single chain simulation. The second-order direct correlation function for the uniform bulk fluid required as input has been calculated from the reference interaction site model integral equation theory using mean spherical approximation. The theoretical results are shown to compare well with the Monte Carlo simulation results for varying densities, chain lengths, and with different attractive interaction parameters. The simulation results on the conformational properties give important indications regarding the behavior of chains as they approach the surfaces.
Theoretical study of excitations in furan: Spectra and molecular dynamics
Authors: Gromov E. V. , Trofimov A. B. , Vitkovskaya N. M. , Köppel H. , Schirmer J. , Meyer H.-D. , Cederbaum L. S.
Published: August 2004

The excitation spectra and molecular dynamics of furan associated with its low-lying excited singlet states A21(3s), B21(V), A11(V′), and B11(3p) are investigated using an ab initio quantum-dynamical approach. The ab initio results of our previous work [J. Chem. Phys. 119, 737 (2003)] on the potential energy surfaces (PES) of these states indicate that they are vibronically coupled with each other and subject to conical intersections. This should give rise to complex nonadiabatic nuclear dynamics. In the present work the dynamical problem is treated using adequate vibronic coupling models accounting for up to four coupled PES and thirteen vibrational degrees of freedom. The calculations were performed using the multiconfiguration time-dependent Hartree method for wave-packet propagation. It is found that in the low-energy region the nuclear dynamics of furan is governed mainly by vibronic coupling of the A21(3s) and B21(V) states, involving also the A11(V′) state. These interactions are responsible for the ultrafast internal conversion from the B21(V) state, characterized by a transfer of the electronic population to the A21(3s) state on a time scale of ∼25 fs. The calculated photoabsorption spectrum of furan is in good qualitative agreement with experimental data. Some assignments of the measured spectrum are proposed.
An explicitly correlated second order Møller-Plesset theory using a frozen Gaussian geminal
Authors: May Andrew J. , Manby Frederick R.
Published: August 2004

A variant of the MP2-R12 class of theories is introduced using an arbitrary geminal function in the place of r12. Integrals are derived for the case where the geminal is expanded in a basis of Gaussian functions in the interelectronic distance. Recurrence relations are derived that do not depend on the exponents of the Gaussian geminals, allowing much of the integration work to be performed after summations over the geminal expansion. Sample calculations at various levels of explicitly correlated MP2 theory are presented for He, Ne, and water.
Structure changes in glassforming liquids upon cooling and compression
Authors: Patashinski Alexander Z. , Ratner Mark A.
Published: August 2004

Upon cooling and compression, both the thermodynamic and the kinetic properties of glassformers change. In fragile glassformers, these changes suggest changes in the local structure of the liquid. Thermodynamic data may then provide a measure of structure changes. Special criteria for structure changes in terms of energy and pressure fluctuations in the isochoric system are proposed; recent theoretical results allow one to rewrite the criteria in terms of long- and short-time thermodynamic characteristics of the liquid. Based on the proposed criteria, we discuss the changes in the local structure due to temperature and pressure variations.
Mass-fractal clustering and power-law decay of cluster size in 1-propanol aqueous solution
Authors: Misawa M. , Dairoku I. , Honma A. , Yamada Y. , Sato T. , Maruyama K. , Mori K. , Suzuki S. , Otomo T.
Published: August 2004

Mesoscale structure of 1-propanol aqueous solutions with propanol mole fraction xp ranging from 0.1 to 0.33 has been studied by means of small angle neutron scattering (SANS) and large-scale reverse Monte Carlo (RMC) technique. Analysis of the SANS intensities in terms of a fractal model shows that the fractal dimension df of mesoscale structure of the solution is about 1.8–1.9 for water-rich solution and about 1.5 for propanol-rich solution. Percolation analysis on the RMC results reveals that the water molecules and the propanol molecules cluster, respectively, as a mass fractal, the dimension dM of which is about 2.3–2.5 for both clusters for water-rich solution. Furthermore, the distribution of the cluster size is expressed by a simple power law with an exponent τ of about 1.35–1.5 for the propanol clusters and 1.05–1.2 for the water clusters. These results imply that the current solution is characterized by polydisperse mass fractals. In fact, a theoretical relation for polydisperse system of mass fractals, df=dM(2−τ), holds well in the current solution. The characteristic change in df from 1.8–1.9 to 1.5 described above is attributed to the crossover between the water-rich regime and the propanol-rich regime. Most of the water molecules and the propanol molecules are located on the interface between clusters, and the water molecules form thin layers of about 10 Å thick irrespective of 1-propanol content studied.
Altered inertial response of generic degrees of freedom
Authors: Melchionna Simone
Published: August 2004

A method to alter the inertial response of generic degrees of freedom is presented. A Hamiltonian acts on the inertial response of a set of independent configurational observables by the introduction of a kinetic bias. The method finds its natural application in reducing the spreading of arbitrary modes in a complex system. The resulting compressed spectrum allows a more efficient sampling of configurational space.
On the phase diagram of reentrant condensation in polyelectrolyte-liposome complexation
Authors: Sennato S. , Bordi F. , Cametti C.
Published: August 2004

Complexation of polyions with oppositely charged spherical liposomes has been investigated by means of dynamic light scattering measurements and a well-defined reentrant condensation has been observed. The phase diagram of charge inversion, recently derived [T. T. Nguyen and B. I. Shklovskii, J. Chem. Phys. 115, 7298 (2001)] for the complexation of DNA with charged spherical macroions, has been employed in order to define the boundaries of the region where polyion-liposome complexes begin to condense, forming larger aggregates, and where aggregates dissolve again, towards isolated polyion-coated-liposome complexes. A reasonable good agreement is observed in the case of complexes formed by negatively charged polyacrylate sodium salt polyions and liposomes built up by cationic lipids (dioleoyltrimethylammoniumpropane), in an extended liposome concentration range.
Energy density analysis of cluster size dependence of surface-molecule interactions: H2, C2H2, C2H4, and CO adsorption onto Si(100)-(2×1) surface
Authors: Nakai Hiromi , Katouda Michio , Kawamura Yoshiumi
Published: August 2004

Adsorption of H2, C2H2, C2H4, and CO onto a Si(100)-(2×1) surface has been treated theoretically using Si12n−3H8n+4 (n=1–4) clusters. The energy density analysis (EDA) proposed by Nakai has been adopted to examine surface-molecule interactions for different cluster sizes. EDA results for the largest model cluster Si45H36 have shown that the adsorption-induced energy density variation in Si atoms decays with distance from the adsorption site. Analysis of this decay, which can be carried out using the EDA technique, is important because it enables verification of the reliability of the model cluster used. In the cases of H2, C2H2, C2H4, and CO adsorption onto the Si(100)-(2×1) surface, it is found that at least a Si21H20 cluster is necessary to treat the surface-molecule interaction with chemical accuracy.
The potential energy surface of the Ar-CO complex obtained using high-resolution data
Authors: Coudert L. H. , Pak I. , Surin L.
Published: August 2004

A potential energy surface is retrieved for the Ar-CO complex by carrying out a global analysis of its high-resolution spectroscopic data. The data set consists of already published microwave and infrared data and of new microwave transitions which are presented in the paper. The theoretical approach used to reproduce the spectrum is based on a model Hamiltonian which accounts simultaneously for the two large amplitude van der Waals modes and for the overall rotation of the complex. Only the vCO=0 state is considered. The root-mean-square deviation of the analysis is 18 MHz for the microwave data and 1.4×10−3 cm−1 for the infrared energy difference data. Fifteen parameters corresponding to the potential energy function are determined in addition to two kinetic energy parameters and two distortion-type parameters. The potential energy surface derived is in good agreement with the one obtained by Shin, Shin, and Tao [J. Chem. Phys. 104, 183 (1996)].
Ab initio molecular-dynamics study of liquid formamide
Authors: Tsuchida Eiji
Published: August 2004

Properties of neat liquid formamide (HCONH2) have been studied by the combination of gradient-corrected density-functional theory, norm-conserving pseudopotentials, and the adaptive finite-element method. The structural and dynamical quantities have been calculated through molecular dynamics simulations under the Born-Oppenheimer approximation. Satisfactory agreement with experimental data was obtained for both intramolecular and intermolecular properties. Our results are also compared with those of the empirical potential functions to clarify their accuracies.
Structural stability and electronic state of transition metal trimers
Authors: Wu Z. J. , Zhang H. J. , Meng J. , Dai Z. W. , Han B. , Jin P. C.
Published: August 2004

Ground state geometries were searched for transition metal trimers Sc3, Y3, La3, Lu3, Ti3, Zr3, and Hf3 by density functional methods. For all the studied trimers, our calculation indicates that the ground state geometries are either equilateral triangle (Zr3 and Hf3) or near equilateral triangle (Ti3, Sc3, Y3, La3, and Lu3). For rare earth trimers Sc3, Y3, La3, and Lu3, isosceles triangle (near equilateral triangle) at quartet state is the ground state. Isosceles triangle at doublet state is the competitive candidate for the ground state. For Zr3 and Hf3, equilateral triangle at singlet state is the most stable. For Ti3, isosceles triangle (near equilateral triangle) at quintet state gives the ground state. For Sc3, Zr3, and Hf3, where experimental results are available, the predicted geometries are in agreement with experiment in which the ground state is equilateral triangle (Zr3) or fluxional (Sc3 and Hf3). For Y3, the calculated geometry is in agreement with experimental observation and previous theoretical study that Y3 is a bent molecule for the ground state. For La3, our calculation is in excellent agreement with previous theoretical study based on density functional methods.
Stark absorption spectroscopy of indole and 3-methylindole
Authors: Jalviste Erko , Ohta Nobuhiro
Published: August 2004

Indole and 3-methylindole (3-MI) doped into a polymethylmethacrylate (PMMA) film are studied by the Stark absorption (electroabsorption) spectroscopy. The La1 and Lb1 absorption bands are distinguished and the change in permanent dipole moment on La1 excitation is determined by a model fit to the measured absorption and electroabsorption spectra. Analysis of the spectra, measured at normal incidence and magic angle conditions, proved the essential role of the electric-field-induced orientation/alignment effects for polar indole and 3-MI molecules in the PMMA environment at room temperature.
H
2
nuclear magnetic resonance study of the molecular motion in cyanoadamantane. I. Supercooled plastically crystalline phase
Authors: Lusceac S. A. , Roggatz I. , Medick P. , Gmeiner J. , Rössler E. A.
Published: August 2004

The supercooled plastically crystalline phase (glassy crystal) of cyanoadamantane was investigated by multidimensional H2 NMR (T>Tg). Although the orientationally disordered crystalline phase always coexisted with the orientationally ordered crystalline phase, we were able to single out the signal from the glassy crystal by selective excitation and it was possible to carry out line shape measurements and two-dimensional (2D) experiments (in frequency and time domain). The latter directly reveal sixfold jumps with an reorientation of the molecular C3 axis via 90° angles, thus reflecting the symmetry of the lattice. The motion around the C3 axis is found to be always fast. We can reproduce the line shape by random walk simulations properly taking into account these molecular motions. Both methods (line shape and 2D experiments) yield time constants which agree with those reported by other techniques. Refining the analysis a narrow distribution of correlation times is introduced to account for a weak stretching of the correlation function. We did not find any indication of a small angle process usually found in structural glasses. Thus, the motional process in the glassy crystal appears to be simple and quite different from that in structural glasses.
Classical density functional study of mixed amphiphile mesostructures
Authors: Christopher P. S. , Oxtoby David W.
Published: August 2004

This paper presents a density functional study of mixed amphiphile solutions. The amphiphiles are modeled using four to seven fused hard spheres where the connectivity is such that the amphiphiles have a proper head group. We present calculations of lamellar and vesicle density distributions, paying particular attention to the morphology of the bilayer structures.
Photodissociation dynamics of 1,2-butadiene at 157 nm
Authors: Mu Xiaolan , Lu I-Chung , Lee Shih-Huang , Wang Xiuyan , Yang Xueming
Published: August 2004

Photodissociation dynamics of 1,2-butadiene at 157 nm has been investigated using a molecular beam apparatus based on photoionization using vacuum ultraviolet synchrotron radiation. Six dissociation pathways have been observed. The observed channels are C4H5+H, C4H4+H2, C3H3+CH3, C2H3+C2H3, C2H4+C2H2, and C4H4+H+H. Among all the dissociation channels, the C3H3+CH3 channel is found to be the dominant process. The product kinetic energy distributions of all dissociation channels have been determined from simulating the experimental time-of-flight spectra. Relative branching ratios for all observed dissociation channels were also estimated based on all detected products.
Molecular description of the collapse of hydrophobic polymer chains in water
Authors: Livadaru Lucian , Kovalenko Andriy
Published: August 2004

We propose a self-consistent molecular theory of conformational properties of flexible polymers in solution. It is applied to the collapse of a hydrophobic polymer chain in water, and can be readily generalized to any polymer-solvent system (e.g., copolymers with high complexity). We stress the potential of this method for a variety of problems, such as protein folding.
NaCl salinity affects lateral root development in Plantago maritima
Authors: Rubinigg Michael , Wenisch Julia , Elzenga J. Theo M. , Stulen Ineke
Published: August 2004

Root growth and morphology were assessed weekly in hydroponically-grown seedlings of the halophyte Plantago maritima L. during exposure to 0, 50, 100 and 200 mm NaCl for 21 d. Relative growth rate was reduced by 25% at 200 mm NaCl. The lower NaCl treatments did not affect relative growth rates. Primary and lateral roots responded differently to NaCl. While primary-root length increased at all NaCl concentrations, total lateral-root length increased at 50 and was not affected at 100 mm but was considerably reduced at 200 mm NaCl. NaCl concentrations of 50 and 100 mm, which had no effect on relative growth rate or total lateral-root length, severely affected root branching pattern in that the number of first, second and third order laterals was reduced. At 200 mm NaCl third order laterals were not formed at all. However, mean lateral-root length was increased at all NaCl concentrations and was highest at 200 mm NaCl. We conclude that the increase in total lateral-root length in plants at 50 and 100 mm NaCl was mainly caused by increased length growth, while the decrease in total lateral-root length at 200 mm was the consequence of inhibition of lateral root primordia and / or the activation of apical meristems rather than reduced length growth.
Detecting interregionally diversifying natural selection on modern human cranial form by using matched molecular and morphometric data
Authors: Roseman Charles C.
Published: August 2004

This comparison of morphological and neutral genetic variation in 10 human populations was designed to test a neutral hypothesis of cranial evolution in living and recent humans and to explain deviations from neutrality where detected. Overall, among-population differences in extantHomo sapienscranial morphology are proportional to among-population differences in neutral molecular characteristics. For most of the populations studied, cranial morphology varies among regions in a manner consistent with neutral expectations. Removal of the effects of shared population history and structure by using the partial Mantel's test, however, does not remove the correlation between some aspects of cranial morphology and a measure of coldness of climate. The excess differentiation is most apparent in those population comparisons that involve a Siberian population living in an extremely cold environment. This finding suggests the action of natural selection, associated with regional variation in temperature, leading to among-population differentiation in excess of neutral expectations for some cranial dimensions. Those dimensions reflect the breadth of the skull, cranial vault size and shape, and aspects of nasal morphology. Although morphology for most of the world appears to vary among populations in accordance with neutral expectations in the context of population structure and history, morphology of the Siberian population appears to have undergone adaptation by natural selection.
Tau induces cooperative Taxol binding to microtubules
Authors: Ross Jennifer L. , Santangelo Christian D. , Makrides Victoria , Fygenson D. Kuchnir
Published: August 2004

Taxol and tau are two ligands that stabilize the microtubule (MT) lattice. Taxol is an anti-mitotic drug that binds β tubulin in the MT interior. Tau is a MT-associated protein that binds both α and β tubulin on the MT exterior. Both Taxol and tau reduce MT dynamics and promote tubulin polymerization. Tau alone also acts to bundle, stiffen, and space MTs. A structural study recently suggested that Taxol and tau may interact by binding to the same site. Using fluorescence recovery after photobleaching, we find that tau induces Taxol to bind MTs cooperatively depending on the tau concentration. We develop a model that correctly fits the data in the absence of tau, yields the equilibrium dissociation constant of ≈2 μM, and determines the escape rate of Taxol through one pore to be 1.7 × 103(M·s)–1. Extension of the model yields a measure of Taxol cooperativity with a Hill coefficient of at least 15 when tau is present at a 1:1 molar ratio with tubulin.
The leukemic fusion gene
AML1-MDS1-EVI1
suppresses
CEBPA
in acute myeloid leukemia by activation of
Calreticulin
Authors: Helbling Daniel , Mueller Beatrice U. , Timchenko Nikolai A. , Hagemeijer Anne , Jotterand Martine , Meyer-Monard Sandrine , Lister Andrew , Rowley Janet D. , Huegli Barbara , Fey Martin F. , Pabst Thomas
Published: August 2004

The leukemic fusion gene
AML1-MDS1-EVI1
(
AME
) encodes a chimeric transcription factor that results from the t(3,21)(q26;q22) translocation seen in patients with acute myeloid leukemia, with therapy-related myelodysplastic syndrome, or with chronic myeloid leukemia in blast crisis. The myeloid transcription factor
CEBPA
is crucial for normal granulopoiesis. Here, we found that conditional expression of AME suppresses CEBPA protein by 90.8% and DNA-binding activity by 93.9%. In contrast,
CEBPA
mRNA levels remained unchanged. In addition, we detected no differences in
CEBPA
mRNA levels in leukemic blasts of patients carrying the
AME
translocation (
n
= 8) compared to acute myeloid leukemia patients with a normal karyotype (
n
= 9). CEBPA protein and binding activity, however, were reduced significantly (100% and 92.1%, respectively) in
AME
patient samples. Furthermore, we observed that calreticulin (
CRT
), a putative inhibitor of CEBPA translation, was strongly activated after induction of AME in the cell-line system (14.8-fold) and in
AME
patient samples (12.2-fold). Moreover, inhibition of CRT by small interfering RNA powerfully restored CEBPA levels. These results identify CEBPA as a key target of the leukemic fusion protein AME and suggest that modulation of CEBPA by CRT may represent a mechanism involved in the differentiation block in
AME
leukemias.
Phosphorylation of hepatitis C virus nonstructural protein 5A modulates its protein interactions and viral RNA replication
Authors: Evans Matthew J. , Rice Charles M. , Goff Stephen P.
Published: August 2004

The study of the hepatitis C virus (HCV) has been hindered by the lack of
in vitro
model systems. The recent development of HCV subgenomic RNA replicons has permitted the study of viral RNA replication in cell culture; however, the requirements for efficient replication of replicons in this system are poorly understood. Many viral isolates do not function as replicons and most require conserved changes, termed adaptive mutations, to replicate efficiently. In this report, we focus on the HCV nonstructural protein 5A (NS5A), a frequent locus for adaptive mutation. We found the interaction between NS5A and human vesicle-associated membrane protein-associated protein A (hVAP-A), a cellular target
N
-ethylmaleimide-sensitive factor attachment protein receptor, to be required for efficient RNA replication: NS5A mutations that blocked interaction with hVAP-A strongly reduced HCV RNA replication. Further analyses revealed an inverse correlation between NS5A phosphorylation and hVAP-A interaction. A subset of the previously identified adaptive mutations suppressed NS5A hyperphosphorylation and promoted hVAP-A binding. Our results support a model in which NS5A hyperphosphorylation disrupts interaction with hVAP-A and negatively regulates viral RNA replication, suggesting that replicon-adaptive mutations act by preventing the phosphorylation-dependent dissociation of the RNA replication complex.
H2-rich fluids from serpentinization: Geochemical and biotic implications
Authors: Sleep N. H. , Meibom A. , Fridriksson Th. , Coleman R. G. , Bird D. K.
Published: August 2004

Metamorphic hydration and oxidation of ultramafic rocks produces serpentinites, composed of serpentine group minerals and varying amounts of brucite, magnetite, and/or FeNi alloys. These minerals buffer metamorphic fluids to extremely reducing conditions that are capable of producing hydrogen gas. Awaruite, FeNi3, forms early in this process when the serpentinite minerals are Fe-rich. Olivine with the current mantle Fe/Mg ratio was oxidized during serpentinization after the Moon-forming impact. This process formed some of the ferric iron in the Earth's mantle. For the rest of Earth's history, serpentinites covered only a small fraction of the Earth's surface but were an important prebiotic and biotic environment. Extant methanogens react H2with CO2to form methane. This is a likely habitable environment on large silicate planets. The catalytic properties of FeNi3allow complex organic compounds to form within serpentinite and, when mixed with atmospherically produced complex organic matter and waters that circulated through basalts, constitutes an attractive prebiotic substrate. Conversely, inorganic catalysis of methane by FeNi3competes with nascent and extant life.
An Ecology of Constraints on e‐Learning in Higher Education: The Case of a Virtual Learning Environment1
Authors: DUTTON WILLIAM H. , HOPE CHEONG PAULINE , PARK AMKEE
Published: August 2004

The implications of e‐learning in higher education have been limited by an array of technical, institutional, social and economic constraints on innovation. This paper describes a case study of the introduction into a university of a widely diffused e‐learning platform: an enterprise‐wide virtual learning environment. The study suggests a variety of patterns and themes tied to the social dynamics of this innovation. These highlight variations across instructors in how the technology was employed, which illuminate the complex ecology surrounding its implementation and use. This offers insights into the faltering development of e‐learning in higher education, and learning more generally.
Commercialisation of Knowledge in Universities: The Case of the Creative Industries
Authors: HEARN GREG , CUNNINGHAM STUART , ORDOÑEZ DIEGO
Published: August 2004

During the last two decades, the convergence of a number of social and economic factors has increased the interest of universities, industry and government in the commercialisation of universities' research output. Not without scepticism from some institutions and individuals, governments and universities around the world are taking steps towards identifying marketable research products, strengthening links with industry, and creating institutional frameworks needed to sustain and increase research output and speed the technology transfer process. These actions vary in degree and scope: from standardising and enforcing conventional intellectual property protection mechanisms, to creating support mechanisms for spin‐off companies and setting up venture capital funds to support their growth.

To date, universities' commercial experience has been mostly in the area of science and technology and thinking about commercialisation is framed in these terms. However, as digital innovations move through the services, media and entertainment sector, innovations and commercialisation opportunities of quite a different nature present themselves. Thus, there are considerable challenges for creative disciplines within tertiary institutions seeking to respond to the commercialisation imperative. This paper examines claims from the emerging creative industries and analyses universities' potential support of the commercialisation of creative innovation.
Human chromokinesin KIF4A functions in chromosome condensation and segregation
Authors: Mazumdar Manjari , Sundareshan Suma , Misteli Tom
Published: August 2004

Accurate chromosome alignment at metaphase and subsequent segregation of condensed chromosomes is a complex process involving elaborate and only partially characterized molecular machinery. Although several spindle associated molecular motors have been shown to be essential for mitotic function, only a few chromosome arm–associated motors have been described. Here, we show that human chromokinesin human HKIF4A (HKIF4A) is an essential chromosome-associated molecular motor involved in faithful chromosome segregation. HKIF4A localizes in the nucleoplasm during interphase and on condensed chromosome arms during mitosis. It accumulates in the mid-zone from late anaphase and localizes to the cytokinetic ring during cytokinesis. RNA interference–mediated depletion of HKIF4A in human cells results in defective prometaphase organization, chromosome mis-alignment at metaphase, spindle defects, and chromosome mis-segregation. HKIF4A interacts with the condensin I and II complexes and HKIF4A depletion results in chromosome hypercondensation, suggesting that HKIF4A is required for maintaining normal chromosome architecture. Our results provide functional evidence that human KIF4A is a novel component of the chromosome condensation and segregation machinery functioning in multiple steps of mitotic division.
Two novel proteins in the mitochondrial outer membrane mediate β-barrel protein assembly
Authors: Ishikawa Daigo , Yamamoto Hayashi , Tamura Yasushi , Moritoh Kaori , Endo Toshiya
Published: August 2004

Mitochondrial outer and inner membranes contain translocators that achieve protein translocation across and/or insertion into the membranes. Recent evidence has shown that mitochondrial β-barrel protein assembly in the outer membrane requires specific translocator proteins in addition to the components of the general translocator complex in the outer membrane, the TOM40 complex. Here we report two novel mitochondrial outer membrane proteins in yeast, Tom13 and Tom38/Sam35, that mediate assembly of mitochondrial β-barrel proteins, Tom40, and/or porin in the outer membrane. Depletion of Tom13 or Tom38/Sam35 affects assembly pathways of the β-barrel proteins differently, suggesting that they mediate different steps of the complex assembly processes of β-barrel proteins in the outer membrane.
Cross characteristic representations of even characteristic symplectic groups
Authors: Guralnick Robert , Tiep Pham
Published: August 2004

We classify the small irreducible representations of

S

p

2
n

(
q
)

Sp_{2n}(q)

with

q
q

even in odd characteristic. This improves even the known results for complex representations. The smallest representation for this group is much larger than in the case when

q
q

is odd. This makes the problem much more difficult.
Radon transforms on affine Grassmannians
Authors: Rubin Boris
Published: August 2004

We develop an analytic approach to the Radon transform

f
^

(
ζ
)
=

∫

τ
⊂
ζ

f
(
τ
)

\hat f (\zeta )=\int _{\tau \subset \zeta } f (\tau )

, where

f
(
τ
)

f(\tau )

is a function on the affine Grassmann manifold

G
(
n
,
k
)

G(n,k)

of

k
k

-dimensional planes in

R

n

\mathbb {R}^n

, and

ζ
\zeta

is a

k
′

k’

-dimensional plane in the similar manifold

G
(
n
,

k
′

)
,

k
′

>
k

G(n,k’), \; k’>k

. For

f
∈

L
p

(
G
(
n
,
k
)
)

f \in L^p (G(n,k))

, we prove that this transform is finite almost everywhere on

G
(
n
,

k
′

)

G(n,k’)

if and only if

1
≤
p
>
(
n
−
k
)

/

(

k
′

−
k
)

\; 1 \le p > (n-k)/(k’ -k)

, and obtain explicit inversion formulas. We establish correspondence between Radon transforms on affine Grassmann manifolds and similar transforms on standard Grassmann manifolds of linear subspaces of

R

n
+
1

\mathbb {R}^{n+1}

. It is proved that the dual Radon transform can be explicitly inverted for

k
+

k
′

≥
n
−
1

k+k’ \ge n-1

, and interpreted as a direct, “quasi-orthogonal" Radon transform for another pair of affine Grassmannians. As a consequence we obtain that the Radon transform and the dual Radon transform are injective simultaneously if and only if

k
+

k
′

=
n
−
1

k+k’ = n-1

. The investigation is carried out for locally integrable and continuous functions satisfying natural weak conditions at infinity.
On the representation of integers as linear combinations of consecutive values of a polynomial
Authors: Boulanger Jacques , Chabert Jean-Luc
Published: August 2004

Let

K
K

be a cyclotomic field with ring of integers

O

K

\mathcal {O}_{K}

and let

f
f

be a polynomial whose values on

Z

\mathbb {Z}

belong to

O

K

\mathcal {O}_{K}

. If the ideal of

O

K

\mathcal {O}_{K}

generated by the values of

f
f

on

Z

\mathbb {Z}

is

O

K

\mathcal {O}_{K}

itself, then every algebraic integer

N
N

of

K
K

may be written in the following form:
\[

N
=

∑

k
=
1

l

ε

k

f
(
k
)

N=\sum _{k=1}^l\;\varepsilon _{k}f(k)

\]
for some integer

l
l

, where the

ε

k

\varepsilon _{k}

’s are roots of unity of

K
K

. Moreover, there are two effective constants

A
A

and

B
B

such that the least integer

l
l

(for a fixed

N
N

) is less than

A

N
~

+
B

A\,\widetilde {N}+B

, where
\[
<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" alttext="upper N overTilde equals max Underscript sigma element-of upper G a l left-parenthesis upper K slash double-struck upper Q right-parenthesis Endscripts StartAbsoluteValue sigma left-parenthesis upper N right-parenthesis EndAbsoluteValue period">

N
~

=

max

σ
∈
G
a
l
(
K

/

Q

)

|
σ
(
N
)
|
.

\widetilde {N}= \max _{\sigma \in Gal(K/\mathbb {Q})} \; \vert \sigma (N) \vert .

\]
Character sums and congruences with 𝑛!
Authors: Garaev Moubariz , Luca Florian , Shparlinski Igor
Published: August 2004

We estimate character sums with

n
!

n!

, on average, and individually. These bounds are used to derive new results about various congruences modulo a prime

p
p

and obtain new information about the spacings between quadratic nonresidues modulo

p
p

. In particular, we show that there exists a positive integer

n
≪

p

1

/

2
+
ε

n\ll p^{1/2+\varepsilon }

such that

n
!

n!

is a primitive root modulo

p
p

. We also show that every nonzero congruence class

a
≢
0

(
mod

p
)

a \not \equiv 0 \pmod p

can be represented as a product of 7 factorials,

a
≡

n
1

!
…

n
7

!

(
mod

p
)

a \equiv n_1! \ldots n_7! \pmod p

, where

max
{

n
i

 

|

 
i
=
1
,
…
,
7
}
=
O
(

p

11

/

12
+
ε

)

\max \{n_i \ |\ i=1,\ldots , 7\}=O(p^{11/12+\varepsilon })

, and we find the asymptotic formula for the number of such representations. Finally, we show that products of 4 factorials

n
1

!

n
2

!

n
3

!

n
4

!
,

n_1!n_2!n_3!n_4!,

with

max
{

n
1

,

n
2

,

n
3

,

n
4

}
=
O
(

p

6

/

7
+
ε

)

\max \{n_1, n_2, n_3, n_4\}=O(p^{6/7+\varepsilon })

represent “almost all” residue classes modulo p, and that products of 3 factorials

n
1

!

n
2

!

n
3

!

n_1!n_2!n_3!

with

max
{

n
1

,

n
2

,

n
3

}
=
O
(

p

5

/

6
+
ε

)

\max \{n_1, n_2, n_3\}=O(p^{5/6+\varepsilon })

are uniformly distributed modulo

p
p

.
Quaternionic algebraic cycles and reality
Authors: dos Santos Pedro , Lima-Filho Paulo
Published: August 2004

In this paper we compute the equivariant homotopy type of spaces of algebraic cycles on real Brauer-Severi varieties, under the action of the Galois group

G
a
l
(

C

/

R

)

Gal({\mathbb C} / {\mathbb R})

. Appropriate stabilizations of these spaces yield two equivariant spectra. The first one classifies Dupont/Seymour’s quaternionic

K
K

-theory, and the other one classifies an equivariant cohomology theory

Z

∗

(
−
)

{\mathfrak Z}^*(-)

which is a natural recipient of characteristic classes

K

H
∗

(
X
)
→

Z

∗

(
X
)

KH^*(X) \to {\mathfrak Z}^*(X)

for quaternionic bundles over Real spaces

X
X

.
A Dominant Mutation in the Pea PHYA Gene Confers Enhanced Responses to Light and Impairs the Light-Dependent Degradation of Phytochrome A
Authors: Weller James L. , Batge Shona L. , Smith Jennifer J. , Kerckhoffs L. Huub J. , Sineshchekov Vitaly A. , Murfet Ian C. , Reid James B.
Published: August 2004

Phytochrome A (phyA) is an important photoreceptor controlling many processes throughout the plant life cycle. It is unique within the phytochrome family for its ability to mediate photomorphogenic responses to continuous far-red light and for the strong photocontrol of its transcript level and protein stability. Here we describe a dominant mutant of garden pea (Pisum sativum) that displays dramatically enhanced responses to light, early photoperiod-independent flowering, and impaired photodestruction of phyA. The mutant carries a single base substitution in the PHYA gene that is genetically inseparable from the mutant phenotype. This substitution is predicted to direct the replacement of a conserved Ala in an N-terminal region of PHYA that is highly divergent between phyA and other phytochromes. This result identifies a region of the phyA photoreceptor molecule that may play an important role in its fate after photoconversion.
Methyl Jasmonate-Induced Ethylene Production Is Responsible for Conifer Phloem Defense Responses and Reprogramming of Stem Cambial Zone for Traumatic Resin Duct Formation
Authors: Hudgins J.W. , Franceschi Vincent R.
Published: August 2004

Conifer stem pest resistance includes constitutive defenses that discourage invasion and inducible defenses, including phenolic and terpenoid resin synthesis. Recently, methyl jasmonate (MJ) was shown to induce conifer resin and phenolic defenses; however, it is not known if MJ is the direct effector or if there is a downstream signal. Exogenous applications of MJ, methyl salicylate, and ethylene were used to assess inducible defense signaling mechanisms in conifer stems. MJ and ethylene but not methyl salicylate caused enhanced phenolic synthesis in polyphenolic parenchyma cells, early sclereid lignification, and reprogramming of the cambial zone to form traumatic resin ducts in Pseudotsuga menziesii and Sequoiadendron giganteum. Similar responses in internodes above and below treated internodes indicate transport of a signal giving a systemic response. Studies focusing on P. menziesii showed MJ induced ethylene production earlier and 77-fold higher than wounding. Ethylene production was also induced in internodes above the MJ-treated internode. Pretreatment of P. menziesii stems with the ethylene response inhibitor 1-methylcyclopropene inhibited MJ and wound responses. Wounding increased 1-aminocyclopropane-1-carboxylic acid (ACC) oxidase protein, but MJ treatment produced a higher and more rapid ACC oxidase increase. ACC oxidase was most abundant in ray parenchyma cells, followed by cambial zone cells and resin duct epithelia. The data show these MJ-induced defense responses are mediated by ethylene. The cambial zone xylem mother cells are reprogrammed to differentiate into resin-secreting epithelial cells by an MJ-induced ethylene burst, whereas polyphenolic parenchyma cells are activated to increase polyphenol production. The results also indicate a central role of ray parenchyma in ethylene-induced defense.
Coordinated Genetic Regulation of Growth and Lignin Revealed by Quantitative Trait Locus Analysis of cDNA Microarray Data in an Interspecific Backcross of Eucalyptus
Authors: Kirst Matias , Myburg Alexander A. , De León José P.G. , Kirst Mariana E. , Scott Jay , Sederoff Ronald
Published: August 2004

Phenotypic, genotypic, and transcript level (microarray) data from an interspecific backcross population of Eucalyptus grandis and Eucalyptus globulus were integrated to dissect the genetic and metabolic network underlying growth variation. Transcript abundance, measured for 2,608 genes in the differentiating xylem of a 91 (E. grandis × E. globulus) × E. grandis backcross progeny was correlated with diameter variation, revealing coordinated down-regulation of genes encoding enzymes of the lignin biosynthesis and associated methylation pathways in fast growing individuals. Lignin analysis of wood samples confirmed the content and quality predicted by the transcript levels measured on the microarrays. Quantitative trait locus (QTL) analysis of transcript levels of lignin-related genes showed that their mRNA abundance is regulated by two genetic loci, demonstrating coordinated genetic control over lignin biosynthesis. These two loci colocalize with QTLs for growth, suggesting that the same genomic regions are regulating growth, and lignin content and composition in the progeny. Genetic mapping of the lignin genes revealed that most of the key biosynthetic genes do not colocalize with growth and transcript level QTLs, with the exception of the locus encoding the enzyme S-adenosylmethionine synthase. This study illustrates the power of integrating quantitative analysis of gene expression data and genetic map information to discover genetic and metabolic networks regulating complex biological traits.
Use of the Fluorescent Timer DsRED-E5 as Reporter to Monitor Dynamics of Gene Activity in Plants
Authors: Mirabella Rossana , Franken Carolien , van der Krogt Gerard N.M. , Bisseling Ton , Geurts René
Published: August 2004

Fluorescent proteins, such as green fluorescent protein and red fluorescent protein (DsRED), have become frequently used reporters in plant biology. However, their potential to monitor dynamic gene regulation is limited by their high stability. The recently made DsRED-E5 variant overcame this problem. DsRED-E5 changes its emission spectrum over time from green to red in a concentration independent manner. Therefore, the green to red fluorescence ratio indicates the age of the protein and can be used as a fluorescent timer to monitor dynamics of gene expression. Here, we analyzed the potential of DsRED-E5 as reporter in plant cells. We showed that in cowpea (Vigna unguiculata) mesophyll protoplasts, DsRED-E5 changes its fluorescence in a way similar to animal cells. Moreover, the timing of this shift is suitable to study developmental processes in plants. To test whether DsRed-E5 can be used to monitor gene regulation in plant organs, we placed DsRED-E5 under the control of promoters that are either up- or down-regulated (MtACT4 and LeEXT1 promoters) or constitutively expressed (MtACT2 promoter) during root hair development in Medicago truncatula. Analysis of the fluorescence ratios clearly provided more accurate insight into the timing of promoter activity.
13C Labeling Reveals Chloroplastic and Extrachloroplastic Pools of Dimethylallyl Pyrophosphate and Their Contribution to Isoprene Formation
Authors: Loreto Francesco , Pinelli Paola , Brancaleoni Enzo , Ciccioli Paolo
Published: August 2004

Isoprene emitted from plants is made in chloroplasts from dimethylallyl pyrophosphate (DMAPP). Leaves of Populus nigra and Phragmites australis exposed to 13CO2 for 15 min emitted isoprene that was about 90% 13C, but DMAPP isolated from those leaves was only 28% and 36% 13C, respectively. The labeled DMAPP is likely to represent chloroplastic DMAPP contributing to isoprene emission. A substantial 13C labeling was also found in both emission and DMAPP pool of low-emitting, young leaves of Phragmites. This confirms that low emission of young leaves is not caused by absence of chloroplastic DMAPP but rather by enzyme characteristics. A very low 13C labeling was found in the DMAPP pool and in the residual isoprene emission of leaves previously fed with fosmidomycin to inhibit isoprene formation. This shows that fosmidomycin is a very effective inhibitor of the chloroplastic biosynthetic pathway of isoprene synthesis, that the residual isoprene is formed from extra-chloroplastic sources, and that chloroplastic and extrachloroplastic pathways are not cross-linked, at least following inhibition of the chloroplastic pathway. Refixation of unlabeled respiratory CO2 in the light may explain incomplete labeling of isoprene emission, as we found a good association between these two parameters.
High Genetic Variability of Herbivore-Induced Volatile Emission within a Broad Range of Maize Inbred Lines
Authors: Degen Thomas , Dillmann Christine , Marion-Poll Frédéric , Turlings Ted C.J.
Published: August 2004

Maize plants (Zea mays) attacked by caterpillars release a mixture of odorous compounds that attract parasitic wasps, natural enemies of the herbivores. We assessed the genetic variability of these induced volatile emissions among 31 maize inbred lines representing a broad range of genetic diversity used by breeders in Europe and North America. Odors were collected from young plants that had been induced by injecting them with caterpillar regurgitant. Significant variation among lines was found for all 23 volatile compounds included in the analysis: the lines differed enormously in the total amount of volatiles emitted and showed highly variable odor profiles distinctive of each genotype. Principal component analysis performed on the relative quantities of particular compounds within the blend revealed clusters of highly correlated volatiles, which may share common metabolic pathways. European and American lines belonging to established heterotic groups were loosely separated from each other, with the most clear-cut difference in the typical release of (E)-β-caryophyllene by European lines. There was no correlation between the distances among the lines based on their odor profiles and their respective genetic distances previously assessed by neutral RFLP markers. This most comprehensive study to date on intraspecific variation in induced odor emission by maize plants provides a further example of the remarkably high genetic diversity conserved within this important crop plant. A better understanding of the genetic control of induced odor emissions may help in the development of maize varieties particularly attractive to parasitoids and other biological control agents and perhaps more repellent for herbivores.
Disorganization of Cortical Microtubules Stimulates Tangential Expansion and Reduces the Uniformity of Cellulose Microfibril Alignment among Cells in the Root of Arabidopsis
Authors: Baskin Tobias I. , Beemster Gerrit T.S. , Judy-March Jan E. , Marga Françoise
Published: August 2004

To test the role of cortical microtubules in aligning cellulose microfibrils and controlling anisotropic expansion, we exposed Arabidopsis thaliana roots to moderate levels of the microtubule inhibitor, oryzalin. After 2 d of treatment, roots grow at approximately steady state. At that time, the spatial profiles of relative expansion rate in length and diameter were quantified, and roots were cryofixed, freeze-substituted, embedded in plastic, and sectioned. The angular distribution of microtubules as a function of distance from the tip was quantified from antitubulin immunofluorescence images. In alternate sections, the overall amount of alignment among microfibrils and their mean orientation as a function of position was quantified with polarized-light microscopy. The spatial profiles of relative expansion show that the drug affects relative elongation and tangential expansion rates independently. The microtubule distributions averaged to transverse in the growth zone for all treatments, but on oryzalin the distributions became broad, indicating poorly organized arrays. At a subcellular scale, cellulose microfibrils in oryzalin-treated roots were as well aligned as in controls; however, the mean alignment direction, while consistently transverse in the controls, was increasingly variable with oryzalin concentration, meaning that microfibril orientation in one location tended to differ from that of a neighboring location. This conclusion was confirmed by direct observations of microfibrils with field-emission scanning electron microscopy. Taken together, these results suggest that cortical microtubules ensure microfibrils are aligned consistently across the organ, thereby endowing the organ with a uniform mechanical structure.