bluuebunny/crossref_metadata_2025 huggingface dataset:
Increasing river discharge in the Eurasian Arctic: Consideration of dams, permafrost thaw, and fires as potential agents of change
Authors: McClelland J. W. , Holmes R. M. , Peterson B. J. , Stieglitz M.
Published: September 2004

Discharge from Eurasian rivers to the Arctic Ocean has increased significantly in recent decades, but the reason for this trend remains unclear. Increased net atmospheric moisture transport from lower to higher latitudes in a warming climate has been identified as one potential mechanism. However, uncertainty associated with estimates of precipitation in the Arctic makes it difficult to confirm whether or not this mechanism is responsible for the change in discharge. Three alternative mechanisms are dam construction and operation, permafrost thaw, and increasing forest fires. Here we evaluate the potential influence of these three mechanisms on changes in discharge from the six largest Eurasian Arctic rivers (Yenisey, Ob', Lena, Kolyma, Pechora, and Severnaya Dvina) between 1936 and 1999. Comprehensive discharge records made it possible to evaluate the influence of dams directly. Data on permafrost thaw and fires in the watersheds of the Eurasian Arctic rivers are more limited. We therefore use a combination of data and modeling scenarios to explore the potential of these two mechanisms as drivers of increasing discharge. Dams have dramatically altered the seasonality of discharge but are not responsible for increases in annual values. Both thawing of permafrost and increased fires may have contributed to changes in discharge, but neither can be considered a major driver. Cumulative thaw depths required to produce the observed increases in discharge are unreasonable: Even if all of the water from thawing permafrost were converted to discharge, a minimum of 4 m thawed evenly across the combined permafrost area of the six major Eurasian Arctic watersheds would have been required. Similarly, sensitivity analysis shows that the increases in fires that would have been necessary to drive the changes in discharge are unrealistic. Of the potential drivers considered here, increasing northward transport of moisture as a result of global warming remains the most viable explanation for the observed increases in Eurasian Arctic river discharge.
Composition and major sources of organic compounds of aerosol particulate matter sampled during the ACE‐Asia campaign
Authors: Simoneit Bernd R. T. , Kobayashi Minoru , Mochida Michihiro , Kawamura Kimitaka , Lee Meehye , Lim Ho‐Jin , Turpin Barbara J. , Komazaki Yuichi
Published: September 2004

The organic compound tracers of atmospheric particulate matter, as well as organic carbon (OC) and elemental carbon (EC), have been characterized for samples acquired during the Asian Pacific Regional Aerosol Characterization Experiment (ACE‐Asia) from Gosan, Jeju Island, Korea, from Sapporo, Japan, and from Chichi‐jima Island in the western North Pacific, as well as on the National Oceanic and Atmospheric Administration R/V Ronald H. Brown. Total extracts were analyzed by gas chromatography–mass spectrometry to determine both polar and aliphatic compounds. Total particles, organic matter, and lipid and saccharide compounds were high during the Asian dust episode (early April 2001) compared to levels at other times. The organic matter can be apportioned to seven emission sources and to significant oxidation‐producing secondary products during long‐range transport. Terrestrial natural background compounds are vascular plant wax lipids derived from direct emission and as part of desert sand dust. Fossil fuel utilization is obvious and derives from petroleum product and coal combustion emissions. Saccharides are a major polar (water‐soluble) carbonaceous fraction derived from soil resuspension (agricultural activities). Biomass‐burning smoke is evident in all samples and seasons. It contributes up to 13% of the total compound mass as water‐soluble constituents. Burning of refuse is another source of organic particles. Varying levels of marine‐derived lipids are superimposed during aerosol transport over the ocean. Secondary oxidation products increase with increasing transport distance and time. The ACE‐Asia aerosols are composed not only of desert dust but also of soil dust, smoke from biomass and refuse burning, and emissions from fossil fuel use in urban areas.
Stratospheric N2O5 in the austral spring 2002 as retrieved from limb emission spectra recorded by the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS)
Authors: Mengistu Tsidu G. , von Clarmann T. , Stiller G. P. , Höpfner M. , Fischer H. , Glatthor N. , Grabowski U. , Kellmann S. , Kiefer M. , Linden A. , Milz M. , Steck T. , Wang D. Y. , Funke B.
Published: September 2004

N2O5 was retrieved from infrared limb emission spectral radiances made by the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) on board the European environmental satellite (ENVISAT). The measurements were taken during the period covering the Antarctic polar vortex split between 20 September and 13 October 2002. The retrieval of N2O5 is aggravated by its continuum‐like emission feature covering a wide spectral region, which is hardly distinguishable from background continuum emission. The method of constraining the background continuum in the N2O5 analysis spectral region to its value in a N2O5‐free spectral region was found to be appropriate to solve this problem. Retrieved volume mixing ratios (VMR) of N2O5 exhibit features consistent with the dynamics prevalent at the time in the Antarctic and known N2O5 chemistry governing diurnal variability. The observations of low N2O5 inside vortex air mass and rich N2O5 exvortex air mass are strongly in support of the chemistry that governs its partitioning within the NOy family. The enhanced nighttime high geographic latitude N2O5 VMR with a peak of 4.4 ppbv in the altitude range of 32–37 km during the last week of September 2002 is consistent with air mass transport from lower to high latitudes and temperature‐sensitive N2O5 formation chemistry. N2O5 enhancement up to 6 ppbv was also observed by the Cryogenic Limb Array Etalon Spectrometer(CLAES) and Improved Stratospheric and Mesospheric Sounder (ISAMS) experiments on Upper Atmospheric Research Satellite (UARS) during Northern Hemisphere January 1992 stratospheric warming which was a factor of 3 larger than any measurements of N2O5 prior to UARS. In contrast, a maximum of 4.4 ppbv N2O5 VMR observed by MIPAS at 32–37 km is only a factor of 2 larger than its prewarming values.
Stimulated Raman backscattering of laser radiation in deep plasma channels
Authors: Kalmykov S. Yu. , Shvets G.
Published: September 2004

Stimulated Raman backscattering (RBS) of intense laser radiation confined by a single-mode plasma channel with a radial variation of plasma frequency greater than a homogeneous-plasma RBS bandwidth is characterized by a strong transverse localization of resonantly driven electron plasma waves (EPW). The EPW localization reduces the peak growth rate of RBS and increases the amplification bandwidth. The continuum of nonbound modes of backscattered radiation shrinks the transverse field profile in a channel and increases the RBS growth rate. Solution of the initial-value problem shows that an electromagnetic pulse amplified by the RBS in the single-mode deep plasma channel has a group velocity higher than in the case of homogeneous-plasma Raman amplification. Implications to the design of a RBS pulse compressor in a plasma channel are discussed.
Wave damping as a critical phenomenon
Authors: Ivanov A. V. , Cairns Iver H. , Robinson P. A.
Published: September 2004

The evolution of a monochromatic Langmuir wave in a collisionless plasma is studied using Vlasov simulations for a wide range of initial amplitudes. Three types of initial electron distributions are considered: Maxwellian, Lorentzian, and dilute warm Maxwellian plus dense cold component. It is shown that there exists a critical initial amplitude ε* that separates the damping and nondamping asymptotic regimes. Depending on the initial amplitude there are three main types of asymptotic evolution: (i) monotonic linear Landau damping below the threshold, ε≪ε*; (ii) the critical case ε≈ε*, when the field damps algebraically as E(t)∝t−3.26; (iii) at ε>ε* initial damping followed by a period of subsequent exponential growth and then irregular oscillations about a nonzero amplitude. This threshold is well described as a critical phenomenon, showing power-law dependencies on the distance from the threshold not only for field quantities, which are expected of second-order phase transitions in thermodynamics, but also for temporal ones. The critical exponent for both the initial damping and growth phases differ from those expected if the threshold is caused by O’Neil’s particle trapping in the wave potential. However, trapping affects the critical exponents well above the threshold and explains the characteristic frequency of oscillations above the threshold. It is found that for a Maxwellian plasma the threshold amplitude ε* corresponds to the condition that the trapping (bounce) frequency ωb equals the modulus of the theoretical Landau damping rate |γL|; at the threshold, qc=ωb/|γL|≈1. For Lorentzian and Maxwellian-plus-cold component plasmas this ratio is qLor≈0.84 and qCM≈0.83, respectively. The temporal and the field scalings are thus interrelated, suggesting that the inclusion of the temporal dimension is vital for critical phenomena in collisionless plasmas, in contrast to thermodynamic systems where the very small characteristic time to achieve equilibrium removes time from the scaling.
Exact solutions for steady reconnective annihilation revisited
Authors: Titov Vyacheslav S. , Tassi Emanuele , Hornig Gunnar
Published: September 2004

This work complements the previous studies on steady reconnective magnetic annihilation in three different geometries: the two-dimensional Cartesian and polar ones and the three-dimensional (3D) cylindrical one. A special class of diffusive solutions is found analytically in explicit form for all of the three geometries. In the 3D case it is extended to a much wider class of exact solutions describing reconnective magnetic annihilation at the separatrix spine line of a magnetic null point. One of the obtained solutions provides an explicit expression for the Craig-Fabling solution. It is also identified which of the steady flow regimes found are dynamically accessible.
Linear coupling and overreflection phenomena of magnetohydrodynamic waves in smooth shear flows
Authors: Gogoberidze G. , Chagelishvili G. D. , Sagdeev R. Z. , Lominadze D. G.
Published: September 2004

Special features of magnetohydrodynamic waves linear dynamics in smooth shear flows are studied. Quantitative asymptotic and numerical analysis are performed for wide range of system parameters when basic flow has constant shear of velocity and uniform magnetic field is parallel to the basic flow. The special features consist of magnetohydrodynamic wave mutual transformation and overreflection phenomena. The transformation takes place for arbitrary shear rates and involves all magnetohydrodynamic wave modes. While the overreflection occurs only for slow magnetosonic and Alfvén waves at high shear rates. Studied phenomena should be decisive in the elaboration of the self-sustaining model of magnetohydrodynamic turbulence in the shear flows.
Yield and hydrodynamic instability versus absorbed energy for a uniformly doped beryllium 250 eV ignition capsule
Authors: Strobel G. L. , Haan S. W. , Munro D. H. , Dittrich T. R. , Marinak M. M. , Suter L. J. , Lindl J. D. , Herrmann M. C.
Published: September 2004

A copper doped beryllium ablator capsule design is geometrically scaled from 190 kJ to 600 kJ absorbed energy for use as an ignition capsule driven at 250 eV on the National Ignition Facility [J. A. Paisner, J. D. Boyes, S. A. Kumpan, W. H. Lowdermilk, and M. S. Sorem, Laser Focus World 30, 75 (1994)]. The capsule design was previously optimized for 190 kJ fixed capsule absorbed energy. The optimization is confirmed at 377 kJ. Two-dimensional simulations are reported that determine surface roughness requirements and tolerance to radiative drive asymmetry over this absorbed energy range.
Spatial relationships and temporal variability in a littoral macrophyte fish assemblage
Authors: Balcombe S. R. , Closs G. P.
Published: September 2004

The presence of macrophytes in lentic systems often exerts a large influence on the spatial and temporal dynamics of the small-bodied fish that inhabit them, particularly in the presence of piscivorous predators. To examine spatial and temporal patterns of fish abundance in macrophyte stands we sampled fish bimonthly with fine-meshed fish traps by day and night in giant rush habitats of a River Murray billabong between October 1995 and September 1996. Three native and three exotic species were found within these habitats during the study, however, catches were dominated by two species of native carp gudgeons (Hypseleotris spp.). Consistently higher numbers of gudgeons were trapped during the day than at night throughout the study period and there was a sustained decline in catch from spring in the first year to the following spring. The results suggest recruitment of juvenile fish spawned during the summer was insufficient for relative abundance to return to the high numbers found at the start of the study. Fine-scale distribution of carp gudgeons within emergent macrophytes was not generally explained by variability in either physical structure or physicochemical variability. This contrasts with many studies of small fish assemblages in macrophytes where piscivorous predators are present.
Abundance indices for main commercial fish species caught by trawl from the south-eastern Australian continental shelf from 1918 to 1957
Authors: Klaer Neil L.
Published: September 2004

Per-haul records of catches by steam trawlers on the south-eastern Australian continental shelf from 1918 to 1957 were examined for the main commercial species tiger flathead (Neoplatycephalus richardsoni), jackass morwong (Nemadactylus macropterus), redfish (Centroberyx affinis), latchet (Pterygotrigla polyommata) and chinaman leatherjacket (Nelusetta ayraudi). Catch rates in weight per haul per species were standardised to annual indices of abundance using a log-linear model. Standardised annual index trends for flathead, latchet and leatherjacket indicate a strong to severe decline during the period covered by the data. All species showed seasonal patterns, but the peak season varied depending on the species. The distribution of standardised catch rate by area also differed greatly by species, and no single area showed consistent differences across all species. Day trawls caught more flathead, redfish and latchet, while night trawls caught more morwong and leatherjacket. Moon phase had less influence on catch rates than other factors. The correlation of annual index trends to a number of annual mean environmental factors was examined and no strong correlations were found.
A model for inferring past conductivity in low salinity waters derived from Murray River (Australia) diatom plankton
Authors: Tibby John , Reid Michael A.
Published: September 2004

Detecting human-induced salinisation in rivers and wetlands of the Murray-Darling Basin has proved problematic. A diatom-based model that permits the estimation of past electrical conductivity (EC) from sedimentary diatom sequences has been developed from Murray River planktonic diatoms. Canonical Correspondence Analysis indicates that EC explains the greatest amount of variance in Murray River planktonic diatoms and that its influence is partially independent of that associated with velocity, turbidity, pH and nutrients. A weighted-averaging based model for inferring past EC was therefore derived from the relationship between diatom composition and EC in Murray River plankton samples. The model works well when comparisons are made between measured and diatom-inferred EC determined by jackknifing based leave-one-out computer resampling (r2jack = 0.71, root-mean-square-error of prediction = 115 μS cm−1). Application of the model will enhance understanding of the nature of pre-European variability in electrical conductivity and permit detection of changes in conductivity through the period of European occupation at key sites. Such reconstructions will provide a firm empirical basis for assessing European impact on aquatic ecosystems and a means by which to assess restoration efforts.
Geographic patterns of genetic diversity in subterranean amphipods of the Pilbara, Western Australia
Authors: Finston Terrie L. , Johnson Michael S.
Published: September 2004

Twenty-six species of subterranean amphipods have been described from the Pilbara, Western Australia, based on variation in morphological characters. Many are known only from single bores. The Pilbara is rich in iron ore, and thus, an understanding of species’ diversity and their distribution is necessary both to manage resources and to conserve fauna. A previous allozyme study of nine bores in a single catchment in the Pilbara found low levels of genetic differentiation among individuals, but the diversity was not associated with single bores. The area studied appeared to contain a single widespread species common to all nine bores, in sympatry with a second, rare species, represented by a single specimen. The present study analysed allozymic variation in amphipods from 26 bores in four additional catchments in the Pilbara, to test the generality of these findings. At each site, samples with similar allelic arrays were found in multiple bores, in sympatry with rare divergent genotypes. Geological complexity was associated with increased genetic differentiation over short geographical distances. With few exceptions, each catchment contained a unique suite of species, suggesting that catchments may form hydrological barriers to gene flow, resulting in local speciation events.
The relationship between sediment and water quality, and riverine sediment loads in the wave-dominated estuaries of south-west Western Australia
Authors: Radke L. C. , Prosser I. P. , Robb M. , Brooke B. , Fredericks D. , Douglas G. B. , Skemstad J.
Published: September 2004

We examine surface sediment and water column total nutrient and chlorophyll a concentrations for 12 estuaries with average water depths <4 m, and calculated sediment loads ranging from 0.2 to 10.8 kg m−2 year−1. Sediment total nitrogen, phosphorus and organic carbon concentrations vary inversely with sediment loads due to: (i) the influx of more mineral-rich sediment into the estuaries; and (ii) increasing sediment sulfidation. Sediment total organic carbon (TOC) : total sulfur (TS) and TS : Fe(II) ratios correlated to sediment loads because enhanced sedimentation increases burial, hence the importance of sulfate reduction in organic matter degradation. Curvilinear relationships were found between a weathering index and organic matter δ13C in sediment, and sediment load. The rising phase of the curve (increasing weathering, lighter isotopic values) at low to intermediate loads relates to soil erosion, whereas regolith or bedrock erosion probably explains the declining phase of the curve (decreasing weathering, heavier isotopic values) at higher sediment loads. The pattern of change for water column total nutrients (nitrogen and phosphorus) with sediment loads is similar to that of the weathering index. Most water quality problems occur in association with soil erosion, and at sediment loads that are intermediate for the estuaries studied. Limited evidence is presented that flushing can moderate the impact of sediment loads upon the estuaries.
Mechanism of action of glatiramer acetate in multiple sclerosis and its potential for the development of new applications
Authors: Arnon Ruth , Aharoni Rina
Published: September 2004

Glatiramer acetate (GA, Copaxone, Copolymer 1) is an approved drug for the treatment of multiple sclerosis and is highly effective in the suppression of experimental autoimmune encephalomyelitis in various species. The mode of action of GA is by initial strong promiscuous binding to MHC molecules and consequent competition with various myelin antigens for their presentation to T cells. A further aspect of its action is potent induction of specific suppressor cells of the T helper 2 (Th2) type that migrate to the brain and lead toin situbystander suppression. Furthermore, the GA-specific cells in the brain express the antiinflammatory cytokines IL-10 and transforming growth factor β, in addition to brain-derived neurotrophic factor, whereas they do not express IFN-γ. Based on this immunomodulatory mode of action, we explored the potential of GA for two other applications: prevention of graft rejection and amelioration of inflammatory bowel diseases. GA was effective in amelioration of graft rejection in two systems by prolongation of skin graft survival and inhibition of functional deterioration of thyroid grafts, across minor and major histocompatibility barriers. In all transplantation systems GA treatment inhibited the detrimental secretion of Th1 inflammatory cytokines and induced beneficial Th2/3 antiinflammatory response. GA was effective also in combination with low-dose immunosuppressive drugs. Inflammatory bowel diseases are characterized by detrimental imbalanced proinflammatory immune reactivity in the gut. GA significantly suppressed the various manifestations of trinitrobenzene sulfonic acid-induced colitis, including mortality, weight loss, and macroscopic and microscopic colonic damage. GA suppressed local lymphocyte proliferations and tumor necrosis factor α detrimental secretion but induced transforming growth factor β, thus confirming the involvement of Th1 to Th2 shift in GA mode of action.
Alkalitolerance: A biological function for a multidrug transporter in pH homeostasis
Authors: Lewinson Oded , Padan Etana , Bibi Eitan
Published: September 2004

MdfA is an
Escherichia coli
multidrug-resistance transporter. Cells expressing MdfA from a multicopy plasmid exhibit multidrug resistance against a diverse group of toxic compounds. In this article, we show that, in addition to its role in multidrug resistance, MdfA confers extreme alkaline pH resistance and allows the growth of transformed cells under conditions that are close to those used normally by alkaliphiles (up to pH 10) by maintaining a physiological internal pH.
MdfA
-deleted
E. coli
cells are sensitive even to mild alkaline conditions, and the wild-type phenotype is restored fully by MdfA expressed from a plasmid. This activity of MdfA requires Na
+
or K
+
. Fluorescence studies with inverted membrane vesicles demonstrate that MdfA catalyzes Na
+
- or K
+
-dependent proton transport, and experiments with reconstituted proteoliposomes confirm that MdfA is solely responsible for this phenomenon. Studies with multidrug resistance-defective MdfA mutants and competitive transport assays suggest that these activities of MdfA are related. Together, the results demonstrate that a single protein has an unprecedented capacity to turn
E. coli
from an obligatory neutrophile into an alkalitolerant bacterium, and they suggest a previously uncharacterized physiological role for MdfA in pH homeostasis.
swi1
- and
swi3
-dependent and independent replication fork arrest at the ribosomal DNA of
Schizosaccharomyces pombe
Authors: Krings Gregor , Bastia Deepak
Published: September 2004

Replication forks are arrested at specific sequences to facilitate a variety of DNA transactions. Forks also stall at sites of DNA damage, and the regression of stalled forks without rescue can cause genetic instability. Therefore, unraveling the mechanisms of fork arrest and of rescue of stalled forks is of considerable general interest. In
Schizosaccharomyces pombe
, products of two mating-type switching genes,
swi1
and
swi3
, participate in fork arrest at the mating-type switch locus. Here, we show that these proteins also act at three termini (Ter) also called replication fork barriers in the spacer regions of rDNA but not at a fourth site, RFP4, which is nonfunctional when present in a plasmid. Two of the Swi1p- and Swi3p-dependent sites were also dependent on the transcription terminator Reb1p. Furthermore, hydroxyurea-induced replication stress mimicked the effect of
swi1
or
swi3
mutations at these sites. A
swi1
mutant that failed to arrest forks at the mating-type fork barrier RTS1 was functional at the rDNA Ter sites, suggesting some specificity of action. Both WT and mutant forms of Swi1p were physically localized at the Ter sites
in vivo
. The results support the notion that Swi1p and Swi3p act at several different protein–DNA complexes in the rDNA spacer regions to arrest replication but that not all fork barriers required their activity to arrest forks.
Guanidine alkaloid analogs as inhibitors of HIV-1 Nef interactions with p53, actin, and p56
lck
Authors: Olszewski Allison , Sato Ken , Aron Zachary D. , Cohen Frederick , Harris Aleishia , McDougall Brenda R. , Robinson W. Edward , Overman Larry E. , Weiss Gregory A.
Published: September 2004

With current anti-HIV treatments targeting only 4 of the 15 HIV proteins, many potential viral vulnerabilities remain unexploited. We report small-molecule inhibitors of the HIV-1 protein Nef. In addition to expanding the anti-HIV arsenal, small-molecule inhibitors against untargeted HIV proteins could be used to dissect key events in the HIV lifecycle. Numerous incompletely characterized interactions between Nef and cellular ligands, for example, present a challenge to understanding molecular events during HIV progression to AIDS. Assays with phage-displayed Nef from HIV
NL4-3
were used to identify a series of guanidine alkaloid-based inhibitors of Nef interactions with p53, actin, and p56
lck
. The guanidines, synthetic analogs of batzellidine and crambescidin natural products, inhibit the Nef–ligand interactions with IC
50
values in the low micromolar range. In addition, sensitive
in vivo
assays for Nef inhibition are reported. Although compounds that are effective
in vitro
proved to be too cytotoxic for cellular assays, the reported Nef inhibitors provide proof-of-concept for disrupting a new HIV target and offer useful leads for drug development.
Solution of Shannon’s problem on the monotonicity of entropy
Authors: Artstein Shiri , Ball Keith , Barthe Franck , Naor Assaf
Published: September 2004

It is shown that if

X
1

,

X
2

,
…

X_1,X_2,\ldots

are independent and identically distributed square-integrable random variables, then the entropy of the normalized sum
\[

Ent
⁡

(

X

1

+
⋯
+

X

n

n

)

\operatorname {Ent} \left (\frac {X_{1}+\cdots + X_{n}}{\sqrt {n}} \right )

\]
is an increasing function of

n
n

. The result also has a version for non-identically distributed random variables or random vectors.
Cycles representing the Todd class of a toric variety
Authors: Pommersheim James , Thomas Hugh
Published: September 2004

In this paper, we describe a way to construct cycles which represent the Todd class of a toric variety. Given a lattice with an inner product, we assign a rational number

μ
(
σ
)

\mu (\sigma )

to each rational polyhedral cone

σ
\sigma

in the lattice, such that for any toric variety

X
X

with fan

Σ
\Sigma

in the lattice, we have
\[
<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" alttext="upper T d left-parenthesis upper X right-parenthesis equals sigma-summation Underscript sigma element-of normal upper Sigma Endscripts mu left-parenthesis sigma right-parenthesis left-bracket upper V left-parenthesis sigma right-parenthesis right-bracket period">

Td
⁡
(
X
)
=

∑

σ
∈
Σ

μ
(
σ
)
[
V
(
σ
)
]
.

\operatorname {Td}(X)=\sum _{\sigma \in \Sigma } \mu (\sigma ) [V(\sigma )].

\]
This constitutes an improved answer to an old question of Danilov. In a similar way, beginning from the choice of a complete flag in the lattice, we obtain the cycle Todd classes constructed by Morelli. Our construction is based on an intersection product on cycles of a simplicial toric variety developed by the second author. Important properties of the construction are established by showing a connection to the canonical representation of the Todd class of a simplicial toric variety as a product of torus-invariant divisors developed by the first author.
Veech surfaces and complete periodicity in genus two
Authors: Calta Kariane
Published: September 2004

We present several results pertaining to Veech surfaces and completely periodic translation surfaces in genus two. A translation surface is a pair

(
M
,
ω
)

(M, \omega )

where

M
M

is a Riemann surface and

ω
\omega

is an Abelian differential on

M
M

. Equivalently, a translation surface is a two-manifold which has transition functions which are translations and a finite number of conical singularities arising from the zeros of

ω
\omega

. A direction

v
v

on a translation surface is completely periodic if any trajectory in the direction

v
v

is either closed or ends in a singularity, i.e., if the surface decomposes as a union of cylinders in the direction

v
v

. Then, we say that a translation surface is completely periodic if any direction in which there is at least one cylinder of closed trajectories is completely periodic. There is an action of the group

S
L
(
2
,

R

)

SL(2, \mathbb {R})

on the space of translation surfaces. A surface which has a lattice stabilizer under this action is said to be Veech. Veech proved that any Veech surface is completely periodic, but the converse is false. In this paper, we use the

J
J

-invariant of Kenyon and Smillie to obtain a classification of all Veech surfaces in the space

H

(
2
)

{\mathcal H}(2)

of genus two translation surfaces with corresponding Abelian differentials which have a single double zero. Furthermore, we obtain a classification of all completely periodic surfaces in genus two.
Hyperbolic cone-manifolds, short geodesics, and Schwarzian derivatives
Authors: Bromberg K.
Published: September 2004

Given a geometrically finite hyperbolic cone-manifold, with the cone-singularity sufficiently short, we construct a one-parameter family of cone-manifolds decreasing the cone-angle to zero. We also control the geometry of this one-parameter family via the Schwarzian derivative of the projective boundary and the length of closed geodesics.
Real bounds, ergodicity and negative Schwarzian for multimodal maps
Authors: van Strien Sebastian , Vargas Edson
Published: September 2004

We consider smooth multimodal maps which have finitely many non-flat critical points. We prove the existence of real bounds. From this we obtain a new proof for the non-existence of wandering intervals, derive extremely useful improved Koebe principles, show that high iterates have ‘negative Schwarzian derivative’ and give results on ergodic properties of the map. One of the main complications in the proofs is that we allow

f
f

to have inflection points.
The threshold for random 𝑘-SAT is 2^{𝑘}log2-𝑂(𝑘)
Authors: Achlioptas Dimitris , Peres Yuval
Published: September 2004

Let

F
k

(
n
,
m
)

F_k(n,m)

be a random

k
k

-CNF formula formed by selecting uniformly and independently

m
m

out of all possible

k
k

-clauses on

n
n

variables. It is well known that if

r
≥

2
k

log
⁡
2

r \geq 2^k \log 2

, then

F
k

(
n
,
r
n
)

F_k(n,rn)

is unsatisfiable with probability that tends to 1 as

n
→
∞

n \to \infty

. We prove that if

r
≤

2
k

log
⁡
2
−

t
k

r \leq 2^k \log 2 - t_k

, where

t
k

=
O
(
k
)

t_k = O(k)

, then

F
k

(
n
,
r
n
)

F_k(n,rn)

is satisfiable with probability that tends to 1 as

n
→
∞

n \to \infty

. Our technique, in fact, yields an explicit lower bound for the random

k
k

-SAT threshold for every

k
k

. For

k
≥
4

k \geq 4

our bounds improve all previously known such bounds.
A monotonicity formula on complete Kähler manifolds with nonnegative bisectional curvature
Authors: Ni Lei
Published: September 2004

In this paper, we derive a new monotonicity formula for the plurisubharmonic functions/positive (1,1) currents on complete Kähler manifolds with nonnegative bisectional curvature. As applications we derive the sharp estimates for the dimension of the spaces of holomorphic functions (sections) with polynomial growth, which, in particular, partially solve a conjecture of Yau. The methods used in this paper, without the assumption of maximum volume of growth, as observed recently by Chen, Fu, Yin, and Zhu, provide a complete solution to Yau’s conjecture.
Regularity of a free boundary in parabolic potential theory
Authors: Caffarelli Luis , Petrosyan Arshak , Shahgholian Henrik
Published: September 2004

We study the regularity of the free boundary in a Stefan-type problem
\[
<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" alttext="normal upper Delta u minus partial-differential Subscript t Baseline u equals chi Subscript normal upper Omega Baseline in upper D subset-of double-struck upper R Superscript n Baseline times double-struck upper R comma u equals StartAbsoluteValue nabla u EndAbsoluteValue equals 0 on upper D minus normal upper Omega">

Δ
u
−

∂
t

u
=

χ
Ω

in 

D
⊂

R

n

×

R

,

u
=

|

∇
u

|

=
0

on 

D
∖
Ω

\Delta u - \partial _t u = \chi _\Omega \quad \text {in $D\subset \mathbb {R}^n\times \mathbb {R}$}, \qquad u = |\nabla u| = 0 \quad \text {on $D\setminus \Omega $}

\]
with no sign assumptions on

u
u

and the time derivative

∂
t

u

\partial _t u

.
Long-Range Interphase Chromosome Organization inDrosophila: A Study Using Color Barcoded Fluorescence In Situ Hybridization and Structural Clustering Analysis
Authors: Lowenstein Michael G. , Goddard Thomas D. , Sedat John W.
Published: September 2004

We have developed a color barcode labeling strategy for use with fluorescence in situ hybridization that enables the discrimination of multiple, identically labeled loci. Barcode labeling of chromosomes provides long-range path information and allows structural analysis at a scale and resolution beyond what was previously possible. Here, we demonstrate the use of a three-color, 13-probe barcode for the structural analysis of Drosophila chromosome 2L in blastoderm stage embryos. We observe the chromosome to be strongly polarized in the Rabl orientation and for some loci to assume defined positions relative to the nuclear envelope. Our analysis indicates packing ∼15- to 28-fold above the 30-nm fiber, which varies along the chromosome in a pattern conserved across embryos. Using a clustering implementation based on rigid body alignment, our analysis suggests that structures within each embryo represent a single population and are effectively modeled as oriented random coils confined within nuclear boundaries. We also found an increased similarity between homologous chromosomes that have begun to pair. Chromosomes in embryos at equivalent developmental stages were found to share structural features and nuclear localization, although size-related differences that correlate with the cell cycle also were observed. The methodology and tools we describe provide a direct means for identifying developmental and cell type-specific features of higher order chromosome and nuclear organization.
Disruption of Yeast Forkhead-associated Cell Cycle Transcription by Oxidative Stress
Authors: Shapira Michael , Segal Eran , Botstein David
Published: September 2004

The effects of oxidative stress on yeast cell cycle depend on the stress-exerting agent. We studied the effects of two oxidative stress agents, hydrogen peroxide (HP) and the superoxide-generating agent menadione (MD). We found that two small coexpressed groups of genes regulated by the Mcm1-Fkh2-Ndd1 transcription regulatory complex are sufficient to account for the difference in the effects of HP and MD on the progress of the cell cycle, namely, G1 arrest with MD and an S phase delay followed by a G2/M arrest with HP. Support for this hypothesis is provided by fkh1fkh2 double mutants, which are affected by MD as we find HP affects wild-type cells. The apparent involvement of a forkhead protein in HP-induced cell cycle arrest, similar to that reported for Caenorhabditis elegans and human, describes a potentially novel stress response pathway in yeast.
Rapid Effects of Retinoic Acid on CREB and ERK Phosphorylation in Neuronal Cells
Authors: Cañón Estela , Cosgaya Jose Miguel , Scsucova Sona , Aranda Ana
Published: September 2004

Retinoic acid (RA) is a potent regulator of neuronal cell differentiation. RA normally activates gene expression by binding to nuclear receptors that interact with response elements (RAREs) in regulatory regions of target genes. We show here that in PC12 cell subclones in which the retinoid causes neurite extension, RA induces a rapid and sustained phosphorylation of CREB (cyclic AMP response element binding protein), compatible with a nongenomic effect. RA also causes a rapid increase of CREB phosphorylation in primary cultures of cerebrocortical cells and of dorsal root ganglia neurons from rat embryos. RA-mediated phosphorylation of CREB leads to a direct stimulation of CREB-dependent transcriptional activity and to activation of the expression of genes such as c-fos, which do not contain RAREs but contain cAMP response elements (CREs) in their promoters. CREB is a major target of extracellular signal regulated kinase ERK1/2 signaling in neuronal cells, and we demonstrate here that RA induces an early stimulation of ERK1/2, which is required both for CREB phosphorylation and transcriptional activity. These results demonstrate that RA, by a nongenomic mechanism, stimulates signaling pathways that lead to phosphorylation of transcription factors, which in turn activate the transcription of genes involved in neuronal differentiation.
EpsinR Is an Adaptor for the SNARE Protein Vti1b
Authors: Hirst Jennifer , Miller Sharon E. , Taylor Marcus J. , von Mollard Gabriele Fischer , Robinson Margaret S.
Published: September 2004

EpsinR is a clathrin-coated vesicle (CCV)-associated protein that binds to vti1b, suggesting that it may be a vti1b-selective adaptor. Depletion of epsinR to undetectable levels in HeLa cells using siRNA causes vti1b to redistribute from the perinuclear region to the cell periphery, but vti1a also redistributes in epsinR-depleted cells, and both vti isoforms redistribute in AP-1–depleted cells. As a more direct assay for epsinR function, we isolated CCVs from control and siRNA-treated cells and then looked for differences in cargo content. In clathrin-depleted cells, both coat and cargo proteins are greatly reduced in this preparation. Knocking down epsinR causes a ∼50% reduction in the amount of AP-1 copurifying with CCVs and vice versa, indicating that the two proteins are dependent on each other for maximum incorporation into the coat. In addition, vti1b, but not vti1a, is reduced by >70% in CCVs from both epsinR- and AP-1–depleted cells. Because AP-1 knockdown reduces the amount of epsinR in CCVs, it is possible that its effect on vti1b may be indirect. These findings provide in vivo evidence that epsinR is an adaptor for vti1b, and they also show that CCV isolation can be used as an assay for adaptor function.
The Role Actin Filaments Play in Providing the Characteristic Curved Form ofDrosophilaBristles
Authors: Tilney Lewis G. , Connelly Patricia S. , Ruggiero Linda , Vranich Kelly A. , Guild Gregory M. , DeRosier David
Published: September 2004

Drosophila bristles display a precise orientation and curvature. An asymmetric extension of the socket cell overlies the newly emerging bristle rudiment to provide direction for bristle elongation, a process thought to be orchestrated by the nerve dendrite lying between these cells. Scanning electron microscopic analysis of individual bristles showed that curvature is planar and far greater near the bristle base. Correlated with this, as development proceeds the pupa gradually recedes from the inner pupal case (an extracellular layer that encloses the pupa) leading to less bristle curvature along the shaft. We propose that the inner pupal case induces elongating bristles to bend when they contact this barrier. During elongation the actin cytoskeleton locks in this curvature by grafting together the overlapping modules that comprise the long filament bundles. Because the bristle is curved, the actin bundles on the superior side must be longer than those on the inferior side. This is accomplished during grafting by greater elongation of superior side modules. Poor actin cross-bridging in mutant bristles results in altered curvature. Thus, the pattern of bristle curvature is a product of both extrinsic factors—the socket cell and the inner pupal case—and intrinsic factors—actin cytoskeleton assembly.
TheCaenorhabditis elegansKinetochore Reorganizes at Prometaphase and in Response to Checkpoint Stimuli
Authors: Stear Jeffrey H. , Roth Mark B.
Published: September 2004

Previous studies of the kinetochore in mammalian systems have demonstrated that this structure undergoes reorganizations after microtubule attachment or in response to activation of the spindle checkpoint. Here, we show that the Caenorhabditis elegans kinetochore displays analogous rearrangements at prometaphase, when microtubule/chromosome interactions are being established, and after exposure to checkpoint stimuli such as nocodazole or anoxia. These reorganizations are characterized by a dissociation of several kinetochore proteins, including HCP-1/CeCENP-F, HIM-10/CeNuf2, SAN-1/CeMad3, and CeBUB-1, from the centromere. We further demonstrate that at metaphase, despite having dissociated from the centromere, these reorganized kinetochore proteins maintain their associations with the metaphase plate. After checkpoint activation, these proteins are detectable as large “flares” that project out laterally from the metaphase plate. Disrupting these gene products via RNA interference results in sensitivity to checkpoint stimuli, as well as defects in the organization of chromosomes at metaphase. These phenotypes suggest that these proteins, and by extension their reorganization during mitosis, are important for mediating the checkpoint response as well as directing the assembly of the metaphase plate.
Apatite-mediated Actin Dynamics in Resorbing Osteoclasts
Authors: Saltel Frédéric , Destaing Olivier , Bard Frédéric , Eichert Diane , Jurdic Pierre
Published: September 2004

The actin cytoskeleton is essential for osteoclasts main function, bone resorption. Two different organizations of actin have been described in osteoclasts, the podosomes belt corresponding to numerous F-actin columns arranged at the cell periphery, and the sealing zone defined as a unique large band of actin. To compare the role of these two different actin organizations, we imaged osteoclasts on various substrata: glass, dentin, and apatite. Using primary osteoclasts expressing GFP-actin, we found that podosome belts and sealing zones, both very dynamic actin structures, were present in mature osteoclasts; podosome belts were observed only in spread osteoclasts adhering onto glass, whereas sealing zone were seen in apico-basal polarized osteoclasts adherent on mineralized matrix. Dynamic observations of several resorption cycles of osteoclasts seeded on apatite revealed that 1) podosomes do not fuse together to form the sealing zone; 2) osteoclasts alternate successive stationary polarized resorption phases with a sealing zone and migration, nonresorption phases without any specific actin structure; and 3) apatite itself promotes sealing zone formation though c-src and Rho signaling. Finally, our work suggests that apatite-mediated sealing zone formation is dependent on both c-src and Rho whereas apico-basal polarization requires only Rho.
DrosophilaCitron Kinase Is Required for the Final Steps of Cytokinesis
Authors: Naim Valeria , Imarisio Sara , Di Cunto Ferdinando , Gatti Maurizio , Bonaccorsi Silvia
Published: September 2004

The mechanisms underlying completion of cytokinesis are still poorly understood. Here, we show that the Drosophila orthologue of mammalian Citron kinases is essential for the final events of the cytokinetic process. Flies bearing mutations in the Drosophila citron kinase (dck) gene were defective in both neuroblast and spermatocyte cytokinesis. In both cell types, early cytokinetic events such as central spindle assembly and contractile ring formation were completely normal. Moreover, cytokinetic rings constricted normally, leading to complete furrow ingression. However late telophases of both cell types displayed persistent midbodies associated with disorganized F actin and anillin structures. Similar defects were observed in dck RNA interference (RNAi) telophases, which, in addition to abnormal F actin and anillin rings, also displayed aberrant membrane protrusions at the cleavage site. Together, these results indicate that mutations in the dck gene result in morphologically abnormal intercellular bridges and in delayed resolution of these structures, suggesting that the wild-type function of dck is required for abscission at the end of cytokinesis. The phenotype of Dck-depleted cells is different from those observed in most Drosophila cytokinesis mutants but extraordinarily similar to that caused by anillin RNAi, suggesting that Dck and anillin are in the same pathway for completion of cytokinesis.
A NIMA-related Kinase, Fa2p, Localizes to a Novel Site in the Proximal Cilia ofChlamydomonasand Mouse Kidney Cells
Authors: Mahjoub Moe R. , Qasim Rasi M. , Quarmby Lynne M.
Published: September 2004

Polycystic kidney disease and related syndromes involve dysregulation of cell proliferation in conjunction with ciliary defects. The relationship between cilia and cell cycle is enigmatic, but it may involve regulation by the NIMA-family of kinases (Neks). We previously showed that the Nek Fa2p is important for ciliary function and cell cycle in Chlamydomonas. We now show that Fa2p localizes to an important regulatory site at the proximal end of cilia in both Chlamydomonas and a mouse kidney cell line. Fa2p also is associated with the proximal end of centrioles. Its localization is dynamic during the cell cycle, following a similar pattern in both cell types. The cell cycle function of Fa2p is kinase independent, whereas its ciliary function is kinase dependent. Mice with mutations in Nek1 or Nek8 have cystic kidneys; therefore, our discovery that a member of this phylogenetic group of Nek proteins is localized to the same sites in Chlamydomonas and kidney epithelial cells suggests that Neks play conserved roles in the coordination of cilia and cell cycle progression.
Multivesicular Body-ESCRT Components Function in pH Response Regulation inSaccharomyces cerevisiaeandCandida albicans
Authors: Xu Wenjie , Smith Frank J. , Subaran Ryan , Mitchell Aaron P.
Published: September 2004

The ESCRT-I, -II, and -III protein complexes function to create multivesicular bodies (MVBs) for sorting of proteins destined for the lysosome or vacuole. Prior studies with Saccharomyces cerevisiae have shown that the ESCRT-III protein Snf7p interacts with the MVB pathway protein Bro1p as well as its homolog Rim20p. Rim20p has no role in MVB formation, but functions in the Rim101p pH-response pathway; Rim20p interacts with transcription factor Rim101p and is required for the activation of Rim101p by C-terminal proteolytic cleavage. We report here that ESCRT-III proteins Snf7p and Vps20p as well as all ESCRT-I and -II proteins are required for Rim101p proteolytic activation in S. cerevisiae. Mutational analysis indicates that the Rim20p N-terminal region interacts with Snf7p, and an insertion in the Rim20p “Bro1 domain” abolishes this interaction, as determined with two-hybrid assays. Disruption of the MVB pathway through mutations affecting non-ESCRT proteins does not impair Rim101p processing. The relationship between the MVB pathway and Rim101p pathway is conserved in Candida albicans, because mutations in four ESCRT subunit genes abolish alkaline pH-induced filamentation, a phenotype previously seen for rim101 and rim20 mutants. The defect is suppressed by expression of C-terminally truncated Rim101-405p, as expected for mutations that block Rim101p proteolytic activation. These results indicate that the ESCRT complexes govern a specific signal transduction pathway and suggest that the MVB pathway may provide a signal that regulates pH-responsive transcription.