bluuebunny/crossref_metadata_2025 huggingface dataset:
GROUPS QUASI-ISOMETRIC TO H2×R
Authors: RIEFFEL ELEANOR G.
Published: April 2007

The most powerful geometric tools are those of differential geometry, but to apply
such techniques to finitely generated groups seems hopeless at first glance since the
natural metric on a finitely generated group is discrete. However Gromov recognized
that a group can metrically resemble a manifold in such a way that geometric results
about that manifold carry over to the group [18, 20]. This resemblance is formalized
in the concept of a ‘quasi-isometry’. This paper contributes to an ongoing program
to understand which groups are quasi-isometric to which simply connected,
homogeneous, Riemannian manifolds [15, 18, 20] by proving that any group
quasi-isometric to H2×R is a finite extension of a cocompact lattice in
Isom(H2×R) or Isom(SL˜(2, R)).
SOLVING THE WORD PROBLEM IN REAL TIME
Authors: HOLT DEREK F. , REES SARAH
Published: April 2007

The paper is devoted to the study of groups whose word problem can be solved by a Turing machine
which operates in real time. A recent result of the first author for word hyperbolic groups is extended to
prove that under certain conditions the generalised Dehn algorithms of Cannon, Goodman and Shapiro,
which clearly run in linear time, can be programmed on real-time Turing machines. It follows that word-hyperbolic
groups, finitely generated nilpotent groups and geometrically finite hyperbolic groups all have
real-time word problems.
PLAIN REPRESENTATIONS OF LIE ALGEBRAS
Authors: BARANOV A. A. , ZALESSKII A. E.
Published: April 2007

In this paper we study representations of finite dimensional Lie algebras. In this
case representations are not necessarily completely reducible. As the general problem
is known to be of enormous complexity, we restrict ourselves to representations that
behave particularly well on Levi subalgebras. We call such representations plain
(Definition 1.1). Informally, we show that the theory of plain representations of a
given Lie algebra L is equivalent to representation theory of finitely many finite
dimensional associative algebras, also non-semisimple. The sense of this is to
distinguish representations of Lie algebras that are of complexity comparable with
that of representations of associative algebras. Non-plain representations are
intrinsically much more complex than plain ones. We view our work as a step toward
understanding this complexity phenomenon.

We restrict ourselves also to perfect Lie algebras L, that is, such that
L = [L, L]. In our main results we assume that L is perfect and
[sfr ][lfr ]2-free (which means that L has no quotient isomorphic to [sfr ][lfr ]2).
The ground field [ ] is always assumed to be algebraically closed and of characteristic 0.
RECURRENCE, DIMENSION AND ENTROPY
Authors: FAN AI-HUA , FENG DE-JUN , WU JUN
Published: April 2007

Let ([sum ]A, T) be a topologically mixing subshift of finite type on an alphabet consisting of m symbols and
let Φ:[sum ]A → Rd
be a continuous function. Denote by σΦ(x) the ergodic limit limn→∞n−1 [sum ]n−1j=0 Φ(Tjx) when the limit exists. Possible ergodic limits are just mean values ∫ Φdμ for all T-invariant measures. For
any possible ergodic limit α, the following variational formula is proved:

[formula here]

where hμ denotes the entropy of μ and htop denotes topological entropy. It is also proved that unless all
points have the same ergodic limit, then the set of points whose ergodic limit does not exist has the same
topological entropy as the whole space [sum ]A
DIRECT SUMS OF OPERATOR SPACES
Authors: OIKHBERG TIMUR
Published: April 2007

It is proved that if X and Y are operator spaces such that every completely bounded operator from X
into Y is completely compact and Z is a completely complemented subspace of X [oplus ] Y, then there exists a
completely bounded automorphism τ: X [oplus ] Y → X [oplus ] Y with completely bounded inverse such that τZ =
X0 [oplus ] Y0, where X0 and Y0 are completely complemented subspaces of X and Y, respectively. If X and Y are
homogeneous, the existence is proved of such a τ under a weaker assumption that any operator from X
to Y is strictly singular. An upper estimate is obtained for
∥τ∥cb∥τ−1∥cb if X and Y are separable
homogeneous Hilbertian operator spaces. Also proved is the uniqueness of a ‘completely unconditional’
basis in X [oplus ] Y if X and Y satisfy certain conditions.
THE BETTI NUMBERS OF THE FREE LOOP SPACE OF A CONNECTED SUM
Authors: LAMBRECHTS PASCAL
Published: April 2007

Let M1 and M2 be two simply connected closed manifolds of the same dimension. It is proved that

(1) if k is a coefficient field such that neither M1 nor M2 has the same cohomology as a sphere, then

the sequence (bk)k[ges ]1 of Betti numbers of the free loop space on M1 #M2 is unbounded;

(2) if, moreover, the cohomology H*(M1;k) is not generated as algebra by only one element, then the

sequence (bk)k[ges ]1 has an exponential growth.

Thanks to theorems of Gromoll and Meyer and of Gromov, this implies, in case 1, that there exist

infinitely many closed geodesics on M1#M2 for each Riemannian metric, and, in case 2, that for a generic

metric, the number of closed geodesics of length [les ]t grows exponentially with t.
A CHARACTERIZATION OF CONVEXITY-PRESERVING MAPS FROM A SUBSET OF A VECTOR SPACE INTO ANOTHER VECTOR SPACE
Authors: ARIYAWANSA K. A. , DAVIDON W. C. , McKENNON K. D.
Published: April 2007

Let V and X be Hausdorff, locally convex, real, topological vector spaces with dim V > 1. It is shown
that a map σ from an open, connected subset of V onto an open subset of X is homeomorphic and
convexity-preserving if and only if σ is projective.
RAMANUJAN'S CLASS INVARIANT λn AND A NEW CLASS OF SERIES FOR 1/π
Authors: CHAN HENG HUAT , LIAW WEN-CHIN , TAN VICTOR
Published: April 2007

On page 212 of his lost notebook, Ramanujan defined a new class invariant λn and constructed a
table of values for λn. The paper constructs a new class of series for 1/π associated with λn. The new
method also yields a new proof of the Borweins' general series for 1/π belonging to Ramanujan's
‘theory of q2’.
AN ACCESS THEOREM FOR CONTINUOUS FUNCTIONS
Authors: BORICHEV ALEXANDER , KLESCHEVICH IGOR
Published: April 2007

Let f be a continuous function on an open subset Ω of ℝ2 such
that for every x ∈ Ω there exists a continuous map γ : [−1, 1] → Ω with γ(0) = x and f ∘ γ increasing on [−1, 1]. Then for every γ ∈ Ω there exists a continuous map γ : [0, 1) → Ω such that γ(0) = y, f ∘ γ is increasing on [0; 1), and
for every compact subset K of Ω, max{t : γ(t) ∈ K} < 1. This result gives
an answer to a question posed by M. Ortel. Furthermore, an example
shows that this result is not valid in higher dimensions.
THE ROTATION NUMBER APPROACH TO EIGENVALUES OF THE ONE-DIMENSIONAL p-LAPLACIAN WITH PERIODIC POTENTIALS
Authors: ZHANG MEIRONG
Published: April 2007

The paper studies the periodic and anti-periodic eigenvalues of the one-dimensional p-Laplacian with
a periodic potential. After a rotation number function ρ(λ) has been introduced, it is proved that for any
non-negative integer n, the endpoints of the interval ρ−1(n/2) in ℝ yield the corresponding periodic or
anti-periodic eigenvalues. However, as in the Dirichlet problem of the higher dimensional p-Laplacian, it
remains open if these eigenvalues represent all periodic and anti-periodic eigenvalues. The result obtained
is a partial generalization of the spectrum theory of the one-dimensional Schrödinger operators with
periodic potentials.
LOGISTIC TYPE EQUATIONS ON ℝN BY A SQUEEZING METHOD INVOLVING BOUNDARY BLOW-UP SOLUTIONS
Authors: DU YIHONG , MA LI
Published: April 2007

We study, on the entire space ℝN(N [ges ] 1), the diffusive logistic equation

and its generalizations. Here p > 1 is a constant. Problem (1.1) plays an important
role in understanding various population models and some other problems in applied
mathematics. When λ = 1 and p = 2, it is also known as the Fisher equation and
KPP equation, due to the pioneering works of Fisher [8] and Kolmogoroff, Petrovsky
and Piscounoff [18].
Interspecific and intraspecific interactions in the monogenean communities of fish: a question of study scale?
Authors: KARVONEN A. , BAGGE A. M. , VALTONEN E. T.
Published: April 2007

Monogenean communities of fish have generally been considered non-interactive as negative interspecific interactions have rarely been reported. Most of the earlier studies on monogenean communities, however, have been conducted not only in systems with relatively low parasite abundances but, more importantly, at study scales where microhabitat-level interactions between the parasites are easily overlooked. We examined the communities of 3 abundant Dactylogyrus (Monogenea) species on the gills of crucian carp (Carassius carassius) by analysing the interactions at the scale of individual gill filaments, where interactions between the species, if any, should most likely take place. Contrary to our expectations, we did not find evidence for competitive exclusion between the species, which suggests that monogenean communities are non-interactive even in high parasite abundances. At the species level, individual parasites were highly aggregated within the filaments, essentially showing a strong tendency to occur at either end of a filament. This, together with the result of differences in the distribution of juvenile parasites within the filaments compared to adults, suggests that these parasites are able to actively seek out their conspecifics in small-scale microhabitats during maturation, which again could enhance their mate-finding.
Two expressions of “surround suppression” in V1 that arise independent of cortical mechanisms of suppression
Authors: TAILBY CHRIS , SOLOMON SAMUEL G. , PEIRCE JONATHAN W. , METHA ANDREW B.
Published: April 2007

The preferred stimulus size of a V1 neuron decreases with increases in stimulus contrast. It has been supposed that stimulus contrast is the primary determinant of such spatial summation in V1 cells, though the extent to which it depends on other stimulus attributes such as orientation and spatial frequency remains untested. We investigated this by recording from single cells in V1 of anaesthetized cats and monkeys, measuring size-tuning curves for high-contrast drifting gratings of optimal spatial configuration, and comparing these curves with those obtained at lower contrast or at sub-optimal orientations or spatial frequencies. For drifting gratings of optimal spatial configuration, lower contrasts produced less surround suppression resulting in increases in preferred size. High contrast gratings of sub-optimal spatial configuration produced more surround suppression than optimal low-contrast gratings, and as much or more surround suppression than optimal high-contrast gratings. For sub-optimal spatial frequencies, preferred size was similar to that for the optimal high-contrast stimulus, whereas for sub-optimal orientations, preferred size was smaller than that for the optimal high-contrast stimulus. These results indicate that, while contrast is an important determinant of spatial summation in V1, it is not the only determinant. Simulation of these experiments on a cortical receptive field modeled as a Gabor revealed that the small preferred sizes observed for non-preferred stimuli could result simply from linear filtering by the classical receptive field. Further simulations show that surround suppression in retinal ganglion cells and LGN cells can be propagated to neurons in V1, though certain properties of the surround seen in cortex indicate that it is not solely inherited from earlier stages of processing.
A three-dimensional analysis of the development of the horizontal cell mosaic in the rat retina: Implications for the mechanisms controlling pattern formation
Authors: NOVELLI ELENA , LEONE PAOLA , RESTA VALENTINA , GALLI-RESTA LUCIA
Published: April 2007

The horizontal cells are known to form a mono-layered mosaic in the adult retina, but are scattered at different retinal depths in early development. To help clarifying when and which spatial constraints appear in the relative positioning of these cells, we have performed a quantitative analysis of the three-dimensional (3D) organization of the horizontal cell mosaic at different developmental stages in the postnatal rat retina. We first analyzed the two-dimensional (2D) distribution of the horizontal cell projections onto a plane parallel to the upper retinal surface in retinal flat-mounts, and thus to the future mature horizontal cell mosaic. We found that this 2D distribution was non random since postnatal day 1 (P1), and had a subsequent stepwise improvement in regularity. This preceded the alignment of cells in a single monolayer, which was observed on P6. We then computed true horizontal cell spacing in 3D, finding non-random 3D positioning already on P1. Simulation studies showed that this order might simply derive from the 2D order observed in the projections of the cells in flat-mount, combined with their limited spread in retinal depth. Throughout the period analyzed, the relative positions of horizontal cells are in good agreement with a minimal spacing rule in which the exclusion zone corresponds to the average size of the inner core of the cell dendritic tree estimated from P1 samples. These data indicate the existence of different phases in the process of horizontal cell 3D spatial ordering, supporting the view that multiple mechanisms are involved in the development of the horizontal cell mosaic.
Low-voltage activated calcium currents in ganglion cells of the tiger salamander retina: Experiment and simulation
Authors: HENDERSON DORI , MILLER ROBERT F.
Published: April 2007

We examined the functional properties of a low-voltage-activated (LVA) calcium current in ganglion cells of the neotenous tiger salamander (Ambystoma tigrinum) retina. Our analysis was based on whole-cell recordings from acutely dissociated ganglion cell bodies identified by retrograde dye injections. Using a continuously perfused cell preparation, the LVA current was isolated with the use of potassium channel blocking agents added to the bathing medium and the pipette solution, while tetrodotoxin was added to the bathing medium to block Na+channels. Approximately 70% of ganglion cells had an easily identified LVA current. The LVA current activated at membrane potentials more positive than −90 mV, and inactivated rapidly. It was relatively insensitive to nickel (IC50 > 500 μM) and amiloride (IC50 > 750 μM). Voltage- and current-clamp studies allowed us to generate a model of this current using the NEURON simulation program. Studies were also carried out to measure the LVA Ca2+current in ganglion cells with dendrites to confirm that it had a significant dendritic representation. Physiological mechanisms that may depend on LVA Ca2+currents are discussed with an emphasis on the role that dendrites play in ganglion cell function.
Complex motion selectivity in PMLS cortex following early lesions of primary visual cortex in the cat
Authors: OUELLETTE B.G. , MINVILLE K. , BOIRE D. , PTITO M. , CASANOVA C.
Published: April 2007

In the cat, the analysis of visual motion cues has generally been attributed to the posteromedial lateral suprasylvian cortex (PMLS) (Toyama et al., 1985; Rauschecker et al., 1987; Rauschecker, 1988; Kim et al., 1997). The responses of neurons in this area are not critically dependent on inputs from the primary visual cortex (VC), as lesions of VC leave neuronal response properties in PMLS relatively unchanged (Spear & Baumann, 1979; Spear, 1988; Guido et al., 1990b). However, previous studies have used a limited range of visual stimuli. In this study, we assessed whether neurons in PMLS cortex remained direction-selective to complex motion stimuli following a lesion of VC, particularly to complex random dot kinematograms (RDKs). Unilateral aspiration of VC was performed on post-natal days 7–9. Single unit extracellular recordings were performed one year later in the ipsilateral PMLS cortex. As in previous studies, a reduction in the percentage of direction selective neurons was observed with drifting sinewave gratings. We report a previously unobserved phenomenon with sinewave gratings, in which there is a greater modulation of firing rate at the temporal frequency of the stimulus in animals with a lesion of VC, suggesting an increased segregation of ON and OFF sub-regions. A significant portion of neurons in PMLS cortex were direction selective to simple (16/18) and complex (11/16) RDKs. However, the strength of direction selectivity to both stimuli was reduced as compared to normals. The data suggest that complex motion processing is still present, albeit reduced, in PMLS cortex despite the removal of VC input. The complex RDK motion selectivity is consistent with both geniculo-cortical and extra-geniculate thalamo-cortical pathways in residual direction encoding.
Normal and rebound impulse firing in retinal ganglion cells
Authors: MITRA PRATIP , MILLER ROBERT F.
Published: April 2007

Given that the action potential output of retinal ganglion cells (RGCs) determines the nature of the visual information that is transmitted from the retina, an understanding of their intrinsic impulse firing characteristics is critical for an appreciation of the overall processing of visual information. Recordings from RGCs within an isolated whole-mount retina preparation showed that their normal impulse firing from the resting membrane potential (RMP) was linearly correlated in its frequency with the stimulus intensity. In addition to describing the relationship between the magnitude of the current injection and the resulting impulse frequency (F/I relationship), we have characterized the properties of individual action potentials when they are elicited from the RMP. In contrast, hyperpolarizing below the RMP revealed that RGCs displayed a time dependent anomalous rectification, manifested by the appearance of a depolarizing sag in their voltage response. When an adequate period of hyperpolarization was terminated, a fast phasic period of “rebound excitation” was observed, characterized by a brief phasic burst of impulse activity. When compared to equivalent action potential firing evoked by depolarizing from the RMP, rebound spiking was associated with a lower threshold and shorter latency for impulse activation as well as a prominent, phasic, burst-like doublet, or triplet of impulses. The rebound action potential had a more positive voltage overshoot and displayed a higher peak rate of rise in its upstroke than those correspondingly generated by depolarizing current pulses from the RMP. Blocking sodium spikes with TTX confirmed that the preceding hyperpolarization led to the recruitment and subsequent generation of a transient depolarizing voltage overshoot, which we have termed the net depolarizing overshoot (NDO). We propose that the NDO boosts the generation of sodium spikes by triggering rebound spikes on its upstroke and crest, thus accounting for the observed voltage dependent change in the firing pattern of RGCs.
Generation, identification and functional characterization of thenob4mutation ofGrm6in the mouse
Authors: PINTO LAWRENCE H. , VITATERNA MARTHA H. , SHIMOMURA KAZUHIRO , SIEPKA SANDRA M. , BALANNIK VICTORIA , MCDEARMON ERIN L. , OMURA CHIAKI , LUMAYAG STEPHEN , INVERGO BRANDON M. , GLAWE BRETT , CANTRELL DONALD R. , INAYAT SAMSOON , OLVERA MARISSA A. , VESSEY KIRSTAN A. , McCALL MAUREEN A. , MADDOX DENNIS , MORGANS CATHERINE W. , YOUNG BRANDON , PLETCHER MATHEW T. , MULLINS ROBERT F. , TROY JOHN B. , TAKAHASHI JOSEPH S.
Published: April 2007

We performed genome-wide chemical mutagenesis of C57BL/6J mice usingN-ethyl-N-nitrosourea (ENU). Electroretinographic screening of the third generation offspring revealed two G3 individuals from one G1 family with a normal a-wave but lacking the b-wave that we namednob4. The mutation was transmitted with a recessive mode of inheritance and mapped to chromosome 11 in a region containing theGrm6gene, which encodes a metabotropic glutamate receptor protein, mGluR6. Sequencing confirmed a single nucleotide substitution from T to C in theGrm6gene. The mutation is predicted to result in substitution of Pro for Ser at position 185 within the extracellular, ligand-binding domain and oocytes expressing the homologous mutation in mGluR6 did not display robust glutamate-induced currents. Retinal mRNA levels forGrm6were not significantly reduced, but no immunoreactivity for mGluR6 protein was found. Histological and fundus evaluations ofnob4showed normal retinal morphology. In contrast, the mutation has severe consequences for visual function. Innob4mice, fewer retinal ganglion cells (RGCs) responded to the onset (ON) of a bright full field stimulus. When ON responses could be evoked, their onset was significantly delayed. Visual acuity and contrast sensitivity, measured with optomotor responses, were reduced under both photopic and scotopic conditions. This mutant will be useful because its phenotype is similar to that of human patients with congenital stationary night blindness and will provide a tool for understanding retinal circuitry and the role of ganglion cell encoding of visual information.
When S-cones contribute to chromatic global motion processing
Authors: RUPPERTSBERG ALEXA I. , WUERGER SOPHIE M. , BERTAMINI MARCO
Published: April 2007

There is common consensus now that color-defined motion can be perceived by the human visual system. For global motion integration tasks based on isoluminant random dot kinematograms conflicting evidence exists, whether observers can (Ruppertsberg et al., 2003) or cannot (Bilodeau & Faubert, 1999) extract a common motion direction for stimuli modulated along the isoluminant red-green axis. Here we report conditions, in which S-cones contribute to chromatic global motion processing. When the display included extra-foveal regions, the individual elements were large (∼0.3°) and the displacement was large (∼1°), stimuli modulated along the yellowish-violet axis proved to be effective in a global motion task. The color contrast thresholds for detection for both color axes were well below the contrasts required for global motion integration, and therefore the discrimination-to-detection ratio was >1. We conclude that there is significant S-cone input to chromatic global motion processing and the extraction of global motion is not mediated by the same mechanism as simple detection. Whether the koniocellular or the magnocellular pathway is involved in transmitting S-cone signals is a topic of current debate (Chatterjee & Callaway, 2002).
Naturalistic color discriminations in polymorphic platyrrhine monkeys: Effects of stimulus luminance and duration examined with functional substitution
Authors: ROWE MICKEY P. , JACOBS GERALD H.
Published: April 2007

X-linked photopigment polymorphism produces six different color vision phenotypes in most species of New World monkey. In the subfamily Callitrichinae, the three M/L alleles underlying these different phenotypes are present at unequal frequencies suggesting that selective pressures other than heterozygous-advantage operate on these alleles. Earlier we investigated this hypothesis with functional substitution, a technique using a computer monitor to simulate colors as they would appear to humans with monkey visual pigments (Visual Neuroscience21:217–222, 2004). The stimuli were derived from measurements of ecologically relevant fruit and foliage. We found that discrimination performance depended on the relative spectral positioning of the substituted M and L pigment pair. Here we have undertaken a systematic examination of two simulation parameters—test field luminance and stimulus duration. Discriminability of the fruit colors depended on which phenotype was simulated but only at short stimulus durations and/or low luminances. Under such conditions, phenotypes with the larger pigment peak separations performed better. At longer durations and higher luminances, differences in performance across different substitutions tended to disappear. The stimuli used in this experiment were analyzed with several color discrimination models. There was limited agreement among the predictions made by these models regarding the capabilities of animals with different pigment pairs and none predicted the dependence of discrimination on changes in luminance and stimulus duration.
Classification of burn severity using Moderate Resolution Imaging Spectroradiometer (MODIS): A case study in the jarrah‐marri forest of southwest Western Australia
Authors: Walz Yvonne , Maier Stefan W. , Dech Stefan W. , Conrad Christopher , Colditz René R.
Published: April 2007

The southwest of Western Australia is a fire‐prone landscape. In this Mediterranean region, prescribed fuel reduction burning is applied as a management tool by the state government's Department of Conservation and Land Management (CALM). Remote sensing data from the Moderate Resolution Imaging Spectroradiometer (MODIS) with multiple observations per day are investigated for operational monitoring of prescribed burning activities.The Normalized Burn Ratio (NBR) is sensitive to the amount of biomass, soil exposure and equivalent water content. The differenced Normalized Burn Ratio (ΔNBR) shows the greatest response of landscape change due to fire. The ratios, originally applied to 30‐m Landsat 7 ETM+ data, have been transferred to 250–500 m MODIS data. The high temporal resolution and direct broadcast capability of MODIS are considered favorable for monitoring prefire and postfire conditions, in particular in near‐real time. This study applies the ΔNBR to classify burn severity using MODIS data with various levels of preprocessing. On the basis of field studies, four burn severity classes are distinguished with best discrimination for high burn severity where the top layer of the vegetation canopy is altered. As expected, the spatial detail of the classifications from MODIS is reduced when compared to results from Landsat 7 ETM+, but the large‐scale spatial patterns are similar. NBR time series of daily data showed that classes of burn severity can be separated for each acquisition date. Large temporal variations of the NBR limit class separation with absolute thresholds, in particular for data uncorrected for effects due to varying viewing geometries. However, MODIS top of atmosphere data allow near‐real‐time assessment of burn severity, important to fire managers for monitoring postfire conditions.
Testing a European winter surface temperature reconstruction in a surrogate climate
Authors: Küttel M. , Luterbacher J. , Zorita E. , Xoplaki E. , Riedwyl N. , Wanner H.
Published: April 2007

We evaluate the skill of a European winter surface air temperature reconstruction over the last 500 years using pseudoproxies obtained from the ECHO‐G and HadCM3 climate models. The emphasis is thereby on the effect of the reduction of available predictors back in time, an issue that has not yet been investigated in detail at continental and seasonal scale. It is found that the key factor in determining the reconstruction skill is the number of predictors and particularly their spatial distribution. However considering the usually insufficient spatial and temporal predictor availability in paleo‐reconstructions, the quality of the predictors becomes more important further back in time. Not surprisingly, the lowest reconstruction skill is found in the early period when the predictor network is reduced. Important differences between ECHO‐G and HadCM3‐based pseudoproxy reconstructions are discussed and implications for future analyses are presented.
Summertime European heat and drought waves induced by wintertime Mediterranean rainfall deficit
Authors: Vautard R. , Yiou P. , D'Andrea F. , de Noblet N. , Viovy N. , Cassou C. , Polcher J. , Ciais P. , Kageyama M. , Fan Y.
Published: April 2007

The risk of extreme heat waves in Europe like the unprecedented one of summer 2003 is likely to increase in the future, calling for increased understanding of these phenomena. From an analysis of meteorological records over 58 years, we show that hot summers are preceded by winter rainfall deficits over Southern Europe. Subsequent drought and heat spreads northward throughout Europe in early summer, due to atmospheric transport of anomalously warm and dry air from Southern Europe in southerly wind episodes. This is shown by the observations and supported by mesoscale meteorological sensitivity simulations for Summer 1994. Moreover previous winter and early spring rainfall frequency in the Mediterranean regions is correlated with summer temperature in central continental Europe. These results emphasize the critical role of the water reservoir in the soil of continental Mediterranean areas for the maintenance of European climate.
A 2000 year atmospheric history of methyl chloride from a South Pole ice core: Evidence for climate‐controlled variability
Authors: Williams Margaret B. , Aydin Murat , Tatum Cheryl , Saltzman Eric S.
Published: April 2007

Methyl chloride (CH3Cl) is a naturally occurring ozone‐depleting gas with a complex biogeochemical cycle involving tropical vegetation, soils, biomass burning and the oceans. This study presents CH3Cl measurements in air extracted from a 300 m ice core from South Pole, Antarctica, covering the time period from 160 BC to 1860 AD. The data exhibit an increasing trend of 3 ppt (parts per trillion) over 100 years and higher frequency variations that appear to be climate‐related. CH3Cl levels were elevated from 900–1300 AD by about 50 ppt relative to the previous 1000 years, coincident with the warm Medieval Climate Anomaly (MCA). CH3Cl levels decreased to a minimum during the Little Ice Age cooling (1650–1800 AD), before rising again to the modern atmospheric level of 550 ppt. These variations most likely reflect changes in tropical and subtropical conditions, and raise the possibility that a warmer future climate may result in higher tropospheric CH3Cl levels.
The effect of a new snow and sea ice albedo scheme on regional climate model simulations
Authors: Køltzow Morten
Published: April 2007

The HIRHAM snow and sea ice albedo scheme and several other existing snow and sea ice albedo parameterizations forced with observed input parameters are compared with observed albedo. For snow on land in non‐forested areas, the original linear temperature‐dependent snow albedo is suggested to be replaced with a polynomial temperature‐dependent scheme. For sea ice albedo none of the evaluated schemes manage to simulate the annual cycle successfully. A suggestion of a new sea ice albedo including the effects of melt ponds, snow on the sea ice and the surface temperature is presented. Simulations with original and new snow and sea ice albedo are performed in the regional atmospheric model HIRHAM and the results are compared. Compared with ERA40 the control simulation with original surface albedo reveals a warm bias during spring in the Arctic. Changing the surface albedo, the biggest differences are found in the same period. Model simulations with old and new surface albedo in HIRHAM clearly reveal that the new albedo scheme is superior to the currently implemented scheme in reproducing the ERA40 temperature climatology. In these experiments the new snow albedo scheme has less impact than the new sea ice albedo. This is probably because areas with changed snow albedo have smaller extent than areas with sea ice in the model setup and are more constraint by the lateral boundaries.
Isotopologue effects during N2O reduction in soils and in pure cultures of denitrifiers
Authors: Ostrom Nathaniel E. , Pitt Adam , Sutka Robin , Ostrom Peggy H. , Grandy A. Stuart , Huizinga Kristin M. , Robertson G. Philip
Published: April 2007

Site preference (SP), the difference in δ15N between the central and outer nitrogen atoms in N2O, is a powerful approach for apportioning fluxes of N2O from soils to nitrification and denitrification (Sutka et al., 2006). A critical aspect of the use of SP data to apportion sources of N2O to nitrification and denitrification is the need to evaluate data for isotope shifts that may have occurred during N2O reduction in soils prior to its escape to the atmosphere. We present data on the isotopologue effects during reduction of N2O during anaerobic incubation of soils and pure cultures of denitrifying bacteria. Isotopic enrichment factors for N2O reduction in soil mesocosms experiments varied between −9.2 and −1.8‰ for nitrogen and between −25.1 and −5.1‰ for oxygen. In pure cultures of Psuedomonas stutzeri and Psuedomonas denitrificans we observed isotopic enrichment factors for SP of −5.0 and −6.8‰, respectively. We further find that N2O consumption produces consistent relationships between δ18O and δ15N and δ18O and the δ15N of the central N atom in N2O of 2.5 and 1.6, respectively, which are clearly diagnostic of this process. Our results indicate that SP may be altered during reduction of N2O and thus bias evaluations of its origins. To understand the impacts of N2O reduction in soil flux studies on source isotope signals we modeled the isotope effects of N2O production occurring simultaneous with reduction and find increasingly curvilinear relationships between δ18O and δ15N and δ18O and δ15Nα with increased reduction. Consequently, a deviation from the linear mixing relationship between soil‐derived and atmospheric N2O is an indication of extensive reduction. On the basis of our characterization of isotopic fractionation during N2O reduction, we show that the rate of reduction would have to be substantially greater than 10% of that of production to impact SP estimates of N2O from denitrification by more than a few percent. Nonetheless, reduction results in a small, but potentially important, increase in SP away from values proposed for bacterial denitrification (0‰) toward those associated with production from nitrification (33‰) (Sutka et al., 2006). On this basis, estimates of the proportion of N2O derived from denitrification obtained from SP values are underestimates and therefore conservative.
Support for an anaerobic sulfur cycle in two Canadian peatland soils
Authors: Blodau Christian , Mayer Bernhard , Peiffer Stefan , Moore Tim R.
Published: April 2007

Sulfur cycling in peatlands may affect global CH4 emissions by suppression of methanogenesis through bacterial sulfate reduction (BSR). We sought evidence for anaerobic sulfur cycling in four peat mesocosms irrigated with sulfate at a loading of 0.8 and 3.3 g S m−2 yr−1. To this end we obtained concentration profiles of dissolved O2, C, S, and Fe, and determined 34S/32S ratios of sulfate, reduced inorganic sulfur (TRIS), and total sulfur. To estimate the importance of BSR for anaerobic respiration, peat was incubated with molybdate as inhibitor of BSR. In the mesocosms, pore water concentrations of dissolved sulfate and H2S adjusted to 5–20 μmol L−1 and 0–9 μmol L−1, respectively, whereas concentrations of CO2, CH4, and DOC reached millimolar levels. CO2 production was not explained by methanogenesis and net reduction of inorganic electron acceptors. In the shallow peat, H2S was produced and 34S in sulfate enriched by 3.6 to 6‰, indicating occurrence of BSR. Sulfate reducers also accounted for much of the metabolic activity. Addition of molybdate suppressed CO2 production by 20 to 50%. Deeper into the peat, the sulfate pool was apparently replenished from the peat matrix as sulfate became enriched in 32S, likely stemming from TRIS or organic sulfur in the peat. Sulfur was thus anaerobically cycled between oxidized and reduced pools. An electron acceptor capable of driving this cycle could not be conclusively identified. Regardless of this uncertainty, the results suggest that anaerobic S cycling can maintain BSR and potentially contribute to low methane production in soils of ombrotrophic bogs.
River networks and ecological corridors: Reactive transport on fractals, migration fronts, hydrochory
Authors: Bertuzzo E. , Maritan A. , Gatto M. , Rodriguez‐Iturbe I. , Rinaldo A.
Published: April 2007

Moving from a recent quantitative model of the US colonization in the 19th century that relies on analytical and numerical results of reactive‐diffusive transport on fractal river networks, this paper considers its generalization to include an embedded flow direction which biases transport. We explore the properties of biased reaction‐dispersal models, in which the reaction rates are described by a logistic equation. The relevance of the work is related to the prediction of the role of hydrologic controls on invasion processes (of species, populations, propagules, or infective agents, depending on the specifics of reaction and transport) occurring in river basins. Exact solutions are obtained along with general numerical solutions, which are applied to fractal constructs like Peano basins and real rivers. We also explore similarities and departures from different one‐dimensional invasion models where a bias is added to both the diffusion and the telegraph equations, considering their respective ecological insight. We find that the geometrical constraints imposed by the fractal networks imply strong corrections on the speed of traveling fronts that can be enhanced or smoothed by the bias. Applications to real river networks show that the chief morphological parameters affecting the front speed are those characterizing the node‐to‐node distances measured along the network structure. The spatial density and number of reactive sites thus prove to be a vital hydrologic control on invasions. We argue that our solutions, currently tied to the validity of the logistic growth, might be relevant to the general study of species' spreading along ecological corridors defined by the river network structure.
Evidence against recent climate‐induced destabilisation of soil carbon from 14C analysis of riverine dissolved organic matter
Authors: Evans Chris D. , Freeman Chris , Cork Lorna G. , Thomas David N. , Reynolds Brian , Billett Michael F. , Garnett Mark H. , Norris David
Published: April 2007

The stability of global soil carbon (C) represents a major uncertainty in forecasting future climate change. In the UK, substantial soil C losses have been reported, while at the same time dissolved organic carbon (DOC) concentrations in upland waters have increased, suggesting that soil C stocks may be destabilising in response to climate change. To investigate the link between soil carbon and DOC at a range of sites, soil organic matter, soilwater and streamwater DOC were analysed for radiocarbon (14C). DOC exported from C‐rich landscapes appears younger than the soil C itself, much of it comprising C assimilated post‐1950s. DOC from more intensively managed, C‐poor soils is older, in some cases >100 years. Results appear consistent with soil C destabilisation in farmed landscapes, but not in peatlands. Reported C losses may to a significant extent be explained by mechanisms other than climate change, e.g. recovery from acidification in peatlands, and agricultural intensification in managed systems.
Effect of chronic CB1 cannabinoid receptor antagonism on livers of rats with biliary cirrhosis
Authors: Yang Ying-Ying , Lin Han-Chieh , Huang Yi-Tsau , Lee Tzung-Yan , Hou Ming-Chih , Wang Ying-Wen , Lee Fa-Yauh , Lee Shou-Dong
Published: April 2007

Recent studies have shown that the activated endocannabinoid system participates in the increase in IHR (intrahepatic resistance) in cirrhosis. The increased hepatic production of vasoconstrictive eicosanoids is involved in the effect of endocannabinoids on the hepatic microcirculation in cirrhosis; however, the mechanisms of these effects are still unknown. The aim of the present study was to investigate the effects of chronic CB1 (cannabinoid 1) receptor blockade in the hepatic microcirculation of CBL (common bile-duct-ligated) cirrhotic rats. After 1 week of treatment with AM251, a specific CB1 receptor antagonist, IHR, SMA (superior mesenteric artery) blood flow and hepatic production of eicosanoids [TXB2 (thromboxane B2), 6-keto PGF1α (prostaglandin F1α) and Cys-LTs (cysteinyl leukotrienes)] were measured. Additionally, the protein levels of hepatic COX (cyclo-oxygenase) isoforms, 5-LOX (5-lipoxygenase), CB1 receptor, TGF-β1 (transforming growth factor β1), cPLA2 [cytosolic PLA2 (phospholipase A2)], sPLA2 (secreted PLA2) and collagen deposition were also measured. In AM251-treated cirrhotic rats, a decrease in portal venous pressure was associated with the decrease in IHR and SMA blood flow. Additionally, the protein levels of hepatic CB1 receptor, TGF-β1, cPLA2 and hepatic collagen deposition, and the hepatic levels of 5-LOX and COX-2 and the corresponding production of TXB2 and Cys-LTs in perfusates, were significantly decreased after 1 week of AM251 treatment in cirrhotic rats. Furthermore, acute infusion of AM251 resulted in a decrease in SMA blood flow and an increase in SMA resistance in CBL rats. In conclusion, the chronic effects of AM251 treatment on the intrahepatic microcirculation were, at least partly, mediated by the inhibition of hepatic TGF-β1 activity, which was associated with decreased hepatic collagen deposition and the activated PLA2/eicosanoid cascade in cirrhotic livers.
Endoskopieturm, Einstellung, Pflege, Dokumentation
Authors: Koithan Werner
Published: April 2007

Seit der Erstveröffentlichung von Bircher im Jahr 1921 hat die Arthroskopie durch Verbesserung der Technik enorme Fortschritte gemacht. Dies gilt für die arthroskopische Optik, die heute für verschiedene Gelenke zwischen 1 und 4 mm variieren kann. Xenon-Lichtquellen sind leistungsstark mit einer Farbtemperatur von 6000°Kelvin. Unter den Lichtkabeln haben sich die Fiberglaskabel im Wesentlichen durchgesetzt, während Fluidkabel für spezielle Einsätze mit möglichst originalgetreuer Wiedergabe der Gelenkstrukturen vorbehalten bleiben. Unter den Kameras sind die Ein- und Dreichip-Kameras sehr verbreitet. Die neuen Entwicklungen gehen auch hier in Richtung Digitalkameras, die auf dem CCD-System beruhen. Damit ist auch die Aufbereitung der Daten in verschiedenen Formaten möglich. Unter den Spülsystemen haben sich 2 Systeme durchgesetzt: Einmal das Pumpensystem über die Rollenpumpe oder die Auffüllung mittels Schwerkraft. Bei den Lagerungen am Schultergelenk hat sich die Seitenlagerung und die Beach-Chair-Position in gleicher Weise durchgesetzt. Die Beach-Chair-Position sollte insbesondere dann gewählt werden, wenn im Anschluss an einen arthroskopischen Eingriff eine offene Rekonstruktion der Rotatorenmanschette oder ventralen Kapsel geplant ist. Die wichtigste Dokumentationsform ist natürlich der Operationsbericht. Daneben haben sich Dokumentationsbögen durchgesetzt und in neuerer Zeit die digitalen Standbildrekorder, mit denen die Speicherung und Archivierung der Bildinformation möglich ist.
Magnetic viscosity phenomena in exchange coupled CoFe∕MnIr bilayers
Authors: Kim Dong Young , Kim C. O. , Tsunoda M. , Yamaguchi M. , Yabugami S. , Takahashi M.
Published: April 2007

The complex permeability spectra were measured in the low (10Hz–1MHz) and microwave (100MHz–9GHz) frequency ranges in CoFe∕MnIr bilayers. The low frequency permeability spectra showed the magnetic viscosity effect below the critical antiferromagnet thickness (tcAF), but not at tAF<tcAF. This effect was analyzed with the dispersed relaxation behavior of an antiferromagnetic (AF) layer coupled with a ferromagnetic layer across the exchange anisotropy (Jc). Over the AF relaxation frequency, the AF spin becomes stable and nearly fixed. Therefore, the Jc can be estimated from the resonance frequency of microwave permeability at tAFtcAF. The discrepancies between dynamic and quasistatic measurements of the Jc only begin to appear in the vicinity of the tcAF and dominate at tAF<tcAF.
Giant magnetoresistance in half metallic Fe3O4 based spin valve structures
Authors: Tripathy D. , Adeyeye A. O.
Published: April 2007

A systematic study of the magnetic and in-plane magnetotransport properties of Fe3O4∕Cu∕Ni80Fe20 spin valve structures is presented. We observed that the spin valve structure is highly sensitive to the thickness of the Cu spacer layer tCu. For tCu=2nm, the structure exhibits a clear anisotropic magnetoresistance at low magnetic fields but no giant magnetoresistance (GMR) effect due to strong exchange coupling between the Fe3O4 and Ni80Fe20 layers. In contrast, a positive GMR effect is measured for tCu⩾5nm due to separate magnetization switching of the Fe3O4 and Ni80Fe20 layers. We have also investigated that the temperature dependence of the GMR effect observed marked changes at low temperatures.
Adsorption-desorption noise influence on mass sensitivity and dynamic range of nanoresonators with rough surfaces
Authors: Palasantzas G.
Published: April 2007

In this work we investigate the influence of adsorption-desorption noise on nanoresonators with random rough surfaces. Indeed, surface roughening leads to an increased number of adsorption sites and thus to an increased limit to mass sensitivity and decreased dynamic range leading to increased nonlinear behavior. Extensive analysis of the surface morphology is necessary because it is not only the roughness amplitude w that contributes to adsorption-desorption noise but also the lateral roughness correlation length ξ, and the roughness exponent H that characterizes short wavelength roughness (<ξ). The latter is shown to have a comparable effect on adsorption-desorption noise as the roughness ratio w∕ξ.
Traces of stable and unstable manifolds in heat flux patterns
Authors: Wingen A. , Jakubowski M. , Spatschek K. H. , Abdullaev S. S. , Finken K. H. , Lehnen M. ,   TEXTOR team
Published: April 2007

Experimental observations of heat fluxes on divertor plates of tokamaks show typical structures (boomerang wings) for varying edge safety factors. The heat flux patterns follow from general principles of nonlinear dynamics. The pattern selection is due to the unstable and stable manifolds of the hyperbolic fixed points of the last intact island chain. Based on the manifold analysis, the experimental observations can be explained in full detail. Quantitative results are presented in terms of the penetration depths of field lines.
Derivation of paleoclassical key hypothesis
Authors: Callen J. D.
Published: April 2007

The paleoclassical model of radial electron heat transport in resistive, current-carrying toroidal plasmas is based on a key hypothesis—that electron guiding centers move and diffuse with radially localized annuli of poloidal magnetic flux. This hypothesis is shown to result from transforming the drift-kinetic-equation to poloidal flux coordinates in situations where this flux is governed by a diffusion equation and analyzing the mathematical characteristic curves (guiding center trajectories) of the resultant drift-kinetic equation on the magnetic field diffusion time scale τη≡a2∕6Dη. These effects add a τη time-scale Fokker-Planck-type spatial diffusion operator to the drift-kinetic equation.