bluuebunny/crossref_metadata_2025 huggingface dataset:
Fusion neutron yield from high intensity laser-cluster interaction
Authors: Davis J. , Petrov G. M. , Velikovich A. L.
Published: June 2006

The fusion neutron yield from a compact neutron source is studied. Laser-irradiated deuterium clusters serve as a precursor of high-energy deuterium ions, which react with the walls of a fusion reaction chamber and produce copious amounts of neutrons in fusion reactions. The explosion of deuterium clusters with initial radius of 50−200Å irradiated by a subpicosecond laser with intensity of 1016W∕cm2 is examined theoretically. We studied the conversion efficiency of laser energy to ion kinetic energy, the mean and maximum ion kinetic energy, and ion energy distribution function by a molecular dynamics model. A yield of ∼105−106 neutrons/J is obtainable for a peak laser intensity of 1016−1017W∕cm2 and clusters with an initial radius of 200–400Å.
Stimulated Raman scattering from individual single-wall carbon nanotubes
Authors: Zhang B. P. , Shimazaki K. , Shiokawa T. , Suzuki M. , Ishibashi K. , Saito R.
Published: June 2006

Individual single-wall carbon nanotubes (SWNTs) exhibited continuous-wave stimulated Raman scattering (SRS). The Raman gain is a few orders higher, and the threshold power is a few orders lower, than values ever reported for other bulk materials and is explained as the result of both the large nonlinear property and efficient electron-phonon interaction in the SWNT. The laser-induced variation of the peak position of the SRS line was likely to depend on the linewidth or tube quality. The results demonstrate the high potential of SWNTs in applications of nanoscale nonlinear optical devices such as wide-range tuneable Raman lasers.
Electrical-optical hybrid pulse-heating method for rapid measurement of high-temperature thermal diffusivity
Authors: Watanabe Hiromichi , Baba Tetsuya
Published: June 2006

An electrical-optical hybrid pulse-heating method has been developed for measuring the thermal diffusivity of conductive materials up to very high temperatures. This method is an integration of the laser flash method and the feedback-controlled current-pulse heating technique. This method can measure the thermal diffusivity even at temperatures above 2500K in less than 1s for a sample initially held at room temperature. The resulting short exposure to high temperature can minimize the contamination of the sample and apparatus. To demonstrate the performance of this method, the thermal diffusivities of molybdenum from 2000to2600K have been determined.
Morphological stability of the Stranski-Krastanow systems under an electric field
Authors: Chiu C.-h. , Poh C. T. , Huang Z.
Published: June 2006

The morphological stability of the Stranski-Krastanow (SK) system against surface undulation is investigated for the case where the SK system consists of a conductor film and a thick substrate and it is under the influence of an electric field induced by an electrode above the film. It is shown that a flat electrode reduces the critical thickness below which the SK system is completely stable against surface undulation. Applying a wavy electrode to the completely stable system, on the other hand, causes the flat film surface to develop into an equilibrium ripple profile.
Light switching via thermo-optic effect of micromachined silicon prism
Authors: Li J. , Liu A. Q. , Zhang X. M. , Zhong T.
Published: June 2006

This letter presents an optical switch using total internal reflection (TIR) via thermo-optic effect (TOE). The switching function is obtained by changing the refractive index of silicon prism via TOE to switch the light across the TIR state. The structure is fabricated by microelectromechanical systems technology. The switch measures a cross talk of >30dB and an extinction ratio of >40dB but exhibits high insertion losses of 31.67 and 18.95dB in the TIR and transmission states, respectively. Compared with conventional micromechanical and light-tuned switches, this switch is unique in mechanism and free of mechanical instability.
Thermal effects on domain orientation of tetragonal piezoelectrics studied byin situx-ray diffraction
Authors: Chang Wonyoung , King Alexander H. , Bowman Keith J.
Published: June 2006

Thermal effects on domain orientation in tetragonal lead zirconate titanate (PZT) and lead titanate (PT) have been investigated by using in situ x-ray diffraction with an area detector. In the case of a soft PZT, it is found that the texture parameter called multiples of a random distribution (MRD) initially increases with temperature up to approximately 100°C and then falls to unity at temperatures approaching the Curie temperature, whereas the MRD of hard PZT and PT initially undergoes a smaller increase or no change. The relationship between the mechanical strain energy and domain wall mobility with temperature is discussed.
Nonlinear size dependence of anatase TiO2 lattice parameters
Authors: Swamy Varghese , Menzies David , Muddle Barry C. , Kuznetsov Alexei , Dubrovinsky Leonid S. , Dai Qing , Dmitriev Vladimir
Published: June 2006

We characterized the size dependence of anatase TiO2 lattice parameters using Rietveld analysis of angle-dispersive synchrotron x-ray diffraction data obtained on a suite of nanocrystalline samples. The refined crystal structure and microstructure data suggest that for crystallites with size less than ∼10nm, the lattice parameters vary nonlinearly. Small lattice expansion, associated with possible increased Ti vacancy and lattice strain, at reduced crystallite size observed in our samples is in contrast to the lattice contraction behavior reported for “pure” anatase nanocrystals. The nonlinear, composition-dependent variation of anatase unit cell volume contrasts with the linear expansion behavior of rutile lattice at finite sizes.
Observation of inversion behaviors induced by polarization effects in GaN∕AlxGa1−xN∕GaN based metal-insulator-semiconductor structures
Authors: Wang M. J. , Shen B. , Wang Y. , Huang S. , Yang Z. J. , Xu K. , Zhang G. Y. , Hoshino K. , Arakawa Y.
Published: June 2006

The influence of the polarization effects on the energy band structures and electrical properties of GaN-based heterostructures has been investigated by means of capacitance-voltage (C-V) measurements of GaN∕Al0.22Ga0.78N∕GaN based metal-insulator-semiconductor (MIS) structures at various frequencies and temperatures. C-V profile shows a distinctive hump at about −10V in the MIS structures, indicating the formation of the inversion mode in the MIS structures. It is thought that the inversion is due to the hole accumulation in the hole well formed at the top GaN∕Al0.22Ga0.78N heterointerface induced by the strong polarization-induced electric fields. The theoretical calculation of the band structure of GaN∕AlxGa1−xN∕GaN heterostructure confirms the physical model for the inversion behaviors.
Perceptual Similarity in Autism
Authors: Bott Lewis , Brock Jon , Brockdorff Noellie , Boucher Jill , Lamberts Koen
Published: June 2006

People with autism have consistently been found to outperform controls on visuo-spatial tasks such as block design, embedded figures, and visual search tasks. Plaisted, O'Riordan, and others (Bonnel et al., 2003; O'Riordan & Plaisted, 2001; O'Riordan, Plaisted, Driver, & Baron-Cohen, 2001; Plaisted, O'Riordan, & Baron-Cohen, 1998a, 1998b) have suggested that these findings might be explained in terms of reduced perceptual similarity in autism, and that reduced perceptual similarity could also account for the difficulties that people with autism have in making generalizations to novel situations. In this study, high-functioning adults with autism and ability-matched controls performed a low-level categorization task designed to examine perceptual similarity. Results were analysed using standard statistical techniques and modelled using a quantitative model of categorization. This analysis revealed that participants with autism required reliably longer to learn the category structure than did the control group but, contrary to the predictions of the reduced perceptual similarity hypothesis, no evidence was found of more accurate performance by the participants with autism during the generalization stage. Our results suggest that when all participants are attending to the same attributes of an object in the visual domain, people with autism will not display signs of enhanced perceptual similarity.
Short Article: Recognition and Attention Guidance during Contextual Cueing in Real-World Scenes: Evidence from Eye Movements
Authors: Brockmole James R. , Henderson John M.
Published: June 2006

When confronted with a previously encountered scene, what information is used to guide search to a known target? We contrasted the role of a scene's basic-level category membership with its specific arrangement of visual properties. Observers were repeatedly shown photographs of scenes that contained consistently but arbitrarily located targets, allowing target positions to be associated with scene content. Learned scenes were then unexpectedly mirror reversed, spatially translating visual features as well as the target across the display while preserving the scene's identity and concept. Mirror reversals produced a cost as the eyes initially moved toward the position in the display in which the target had previously appeared. The cost was not complete, however; when initial search failed, the eyes were quickly directed to the target's new position. These results suggest that in real-world scenes, shifts of attention are initially based on scene identity, and subsequent shifts are guided by more detailed information regarding scene and object layout.
Short Article: Sequential Tapping Interferes Selectively with Multiple-Object Tracking: Do Finger-Tapping and Tracking Share a Common Resource?
Authors: Trick Lana M. , Guindon Jeannine , Vallis Lori A.
Published: June 2006

Multiple-object tracking involves simultaneously monitoring positions of a number of target items as they move among distractors. Young adults are capable of tracking only 3–5 items at once. In this study we investigated the origin of this limitation by looking for secondary tasks that interfere with tracking. We compared tracking performance (baseline condition), with performance when participants tapped three fingers in a specific order while tracking (sequential tapping) or articulated three syllables in a specific order while tracking (sequential articulation). The articulation task was used to ensure that the interference produced by sequential tapping was more than would be expected by the executive demands of carrying out any two “attention-demanding” tasks at once. Even though sequential tapping does not require vision or memorizing the positions of external items, it produced significantly more interference than did sequential articulation, as might be expected if tracking and sequential tapping shared a common (limited) resource.
The length of a shortest closed geodesic and the area of a 2-dimensional sphere
Authors: Rotman R.
Published: June 2006

Let

M
M

be a Riemannian manifold homeomorphic to

S
2

S^2

. The purpose of this paper is to establish the new inequality for the length of a shortest closed geodesic,

l
(
M
)

l(M)

, in terms of the area

A
A

of

M
M

. This result improves previously known inequalities by C.B. Croke (1988), by A. Nabutovsky and the author (2002) and by S. Sabourau (2004).
Convex dominates concave: An exclusion principle in discrete-time Kolmogorov systems
Authors: Kon Ryusuke
Published: June 2006

We establish an exclusion principle in discrete-time Kolmogorov systems by using average Liapunov functions. The exclusion principle shows that a weakly dominant species with a convex logarithmic growth rate function eliminates species with concave logarithmic growth rate functions. A general result is applied to specific population models. This application gives an improved exclusion principle for the specific population models.
Asymptotically cylindrical Ricci-flat manifolds
Authors: Salur Sema
Published: June 2006

Asymptotically cylindrical Ricci-flat manifolds play a key role in constructing Topological Quantum Field Theories. It is particularly important to understand their behavior at the cylindrical ends and the natural restrictions on the geometry. In this paper we show that an orientable, connected, asymptotically cylindrical manifold(M,g)(M,g)with Ricci-flat metricggcan have at most two cylindrical ends. In the case where there are two such cylindrical ends, then there is reduction in the holonomy group Hol(g)(g)and(M,g)(M,g)is a cylinder.
A remark on the Kochen-Specker theorem and some characterizations of the determinant on sets of Hermitian matrices
Authors: Molnár Lajos
Published: June 2006

In this paper we describe the general forms of all (nonlinear) continuous functionals on the sets of positive definite, positive semi-definite and Hermitian matrices which are multiplicative on the commuting elements. As a consequence, we obtain some new characterizations of the determinant on those classes of matrices.
Maximality of sums of two maximal monotone operators
Authors: Borwein Jonathan
Published: June 2006

We use methods from convex analysis, relying on an ingenious function of Simon Fitzpatrick, to prove maximality of the sum of two maximal monotone operators on reflexive Banach space under weak transversality conditions.
Commutants of certain analytic operator algebras
Authors: Ji Guoxing , Ohwada Tomoyoshi , Saito Kichi-Suke
Published: June 2006

We prove that algebraic commutants of maximal subdiagonal algebras and of analytic operator algebras determined by flows in a

σ
\sigma

-finite von Neumann algebra are self-adjoint.
Markov traces on cyclotomic Temperley–Lieb algebras
Authors: Rui Hebing
Published: June 2006

In this note, we use generalized Tchebychev polynomials to define a trace function which satisfies certain conditions. Such a trace will be called the Markov trace. In particular, we obtain formulae for the weights of the Markov trace. As a corollary, we get a combinatorial identity. This generalizes Jones’s 1983 result on Temperley–Lieb algebras.
Open subgroups and the centre problem for the Fourier algebra
Authors: Hu Zhiguo
Published: June 2006

Let

A
(
G
)

A(G)

be the Fourier algebra of a locally compact group and

U
C
B
(

G
^

)

UCB(\hat {G})

the

C
∗

C^*

-algebra of uniformly continuous linear functionals on

A
(
G
)

A(G)

. We study how the centre problem for the algebra

U
C
B
(

G
^

)
∗

UCB(\hat {G})^*

(resp.

A
(
G

)

∗
∗

A(G)^{**}

) is related to the centre problem for the algebras

U
C
B
(

H
^

)
∗

UCB(\hat {H})^*

(resp.

A
(
H

)

∗
∗

A(H)^{**}

) of

σ
\sigma

-compact open subgroups

H
H

of

G
G

. We extend some results of Lau-Losert on the centres of

U
C
B
(

G
^

)
∗

UCB(\hat {G})^*

and

A
(
G

)

∗
∗

A(G)^{**}

.
Two characterizations of pure injective modules
Authors: Divaani-Aazar Kamran , Esmkhani Mohammad , Tousi Massoud
Published: June 2006

Let

R
R

be a commutative ring with identity and

D
D

an

R
R

-module. It is shown that if

D
D

is pure injective, then

D
D

is isomorphic to a direct summand of the direct product of a family of finitely embedded modules. As a result, it follows that if

R
R

is Noetherian, then

D
D

is pure injective if and only if

D
D

is isomorphic to a direct summand of the direct product of a family of Artinian modules. Moreover, it is proved that

D
D

is pure injective if and only if there is a family

{

T
λ

}

λ
∈
Λ

\{T_\lambda \}_{\lambda \in \Lambda }

of

R
R

-algebras which are finitely presented as

R
R

-modules, such that

D
D

is isomorphic to a direct summand of a module of the form

∏

λ
∈
Λ

E
λ

\prod _{\lambda \in \Lambda }E_\lambda

, where for each

λ
∈
Λ

\lambda \in \Lambda

,

E
λ

E_\lambda

is an injective

T
λ

T_\lambda

-module.
On 𝐿¹-norms of meromorphic functions with fixed poles
Authors: Baranov A.
Published: June 2006

We study boundedness of the differentiation and embedding operators in the shift-coinvariant subspaces

K
B
1

{K_B^1}

generated by Blaschke products with sparse zeros, that is, in the spaces of meromorphic functions with fixed poles in the lower half-plane endowed with

L
1

L^1

-norm. We answer negatively the question of K.M. Dyakonov about the necessity of the condition

B
′

∈

L
∞

(

R

)

B’\in L^\infty (\mathbb {R})

for the boundedness of the differentiation on

K
B
1

{K_B^1}

. Our main tool is a construction of an unconditional basis of rational fractions in

K
B
1

{K_B^1}

.
Minimizing Euler characteristics of symplectic four-manifolds
Authors: Kotschick D.
Published: June 2006

We prove that the minimal Euler characteristic of a closed symplectic four-manifold with given fundamental group is often much larger than the minimal Euler characteristic of almost complex closed four-manifolds with the same fundamental group. In fact, the difference between the two is arbitrarily large for certain groups.
Asymptotic phase and invariant foliations near periodic orbits
Authors: Dumortier Freddy
Published: June 2006

The paper deals with asymptotic phase and invariant foliations near periodic orbits, extending for two-dimensional smooth vector fields results that have been obtained by Chicone and Liu (2004). The problem of the existence of asymptotic phase is completely solved for analytic vector fields and is reduced to a problem of infinite codimension for

C

∞

C^{\infty }

systems. Moreover it is proven that whenever asymptotic phase occurs, or in other words, when the periodic orbit is isochronous, then there also exists a

C

∞

C^{\infty }

foliation, with leaves transversally cutting the periodic orbit and invariant under the flow of the vector field. The paper also provides some results in three dimensions.
Hyperbolic surfaces with prescribed infinite symmetry groups
Authors: Allcock Daniel
Published: June 2006

For any countable group

G
G

whatsoever, there is a complete hyperbolic surface whose isometry group is

G
G

.
Lehmer 𝑘-tuples
Authors: Alkan Emre , Stan Florin , Zaharescu Alexandru
Published: June 2006

Generalizing a classical problem of Lehmer, in this paper we provide an asymptotic result for the number of Lehmer

k
k

-tuples.
On the irreducibility of the Hilbert scheme of space curves
Authors: Iliev Hristo
Published: June 2006

Denote by

H

d
,
g
,
r

H_{d,g,r}

the Hilbert scheme parametrizing smooth irreducible complex curves of degree

d
d

and genus

g
g

embedded in

P

r

\mathbb {P}^r

. In 1921 Severi claimed that

H

d
,
g
,
r

H_{d,g,r}

is irreducible if

d
≥
g
+
r

d \geq g+r

. As it has turned out in recent years, the conjecture is true for

r
=
3

r = 3

and

4
4

, while for

r
≥
6

r \geq 6

it is incorrect. We prove that

H

g
,
g
,
3

H_{g,g,3}

,

H

g
+
3
,
g
,
4

H_{g+3,g,4}

and

H

g
+
2
,
g
,
4

H_{g+2,g,4}

are irreducible, provided that

g
≥
13

g \geq 13

,

g
≥
5

g \geq 5

and

g
≥
11

g \geq 11

, correspondingly. This augments the results obtained previously by Ein (1986), (1987) and by Keem and Kim (1992).
A selection theorem in metric trees
Authors: Aksoy A. , Khamsi M.
Published: June 2006

In this paper, we show that nonempty closed convex subsets of a metric tree enjoy many properties shared by convex subsets of Hilbert spaces and admissible subsets of hyperconvex spaces. Furthermore, we prove that a set-valued mappingT∗T^*of a metric treeMMwith convex values has a selectionT:M→MT: M\rightarrow Mfor which<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" alttext="d left-parenthesis upper T left-parenthesis x right-parenthesis comma upper T left-parenthesis y right-parenthesis right-parenthesis less-than-or-equal-to d Subscript upper H Baseline left-parenthesis upper T Superscript asterisk Baseline left-parenthesis x right-parenthesis comma upper T Superscript asterisk Baseline left-parenthesis y right-parenthesis right-parenthesis">d(T(x),T(y))≤dH(T∗(x),T∗(y))d(T(x),T(y))\leq d_H(T^*(x),T^*(y))for eachx,y∈Mx,y \in M. Here bydHd_Hwe mean the Hausdroff distance. Many applications of this result are given.
Characters of 𝑝’-degree with cyclotomic field of values
Authors: Navarro Gabriel , Tiep Pham
Published: June 2006

If

p
p

is a prime number and

G
G

is a finite group, we show that

G
G

has an irreducible complex character of degree not divisible by

p
p

with values in the cyclotomic field

Q

p

\mathbb {Q}_p

.
A remark on the monomial conjecture and Cohen-Macaulay canonical modules
Authors: Nhan Le Thanh
Published: June 2006

In this paper, some sufficient conditions for rings and modules to satisfy the monomial conjecture are given. A characterization of Cohen-Macaulay canonical modules is presented.
Simulation and quantification of enrichment and retention processes in the southern Benguela upwelling ecosystem
Authors: LETT CHRISTOPHE , ROY CLAUDE , LEVASSEUR ANNE , VAN DER LINGEN CARL D. , MULLON CHRISTIAN
Published: June 2006

Important environmental processes for the survival and recruitment of early life stages of pelagic fishes have been synthesized through Bakun's fundamental triad as enrichment, concentration and retention processes (A. Bakun, 1996, Patterns in the Ocean. Ocean Processes and Marine Population Dynamics. San Diego, CA, USA: University of California Sea Grant). This conceptual framework states that from favourable spawning habitats, eggs and larvae would be transported to and/or retained in places where food originating from enrichment areas would be concentrated. We propose a method for quantifying two of the triad processes, enrichment and retention, based on the Lagrangian tracking of particles transported within water velocity fields generated by a three‐dimensional hydrodynamic model. We apply this method to the southern Benguela upwelling ecosystem, constructing putative maps of enrichment and retention. We comment on these maps regarding main features of the circulation in the region, and investigate seasonal variability of the processes. We finally discuss the results in relation to available knowledge on the reproductive strategies of two pelagic clupeoid species abundant in the southern Benguela, anchovy (Engraulis encrasicolus) and sardine (Sardinops sagax). Our approach is intended to be sufficiently generic so as to allow its application to other upwelling systems.
Predator related oviposition site selection of aquatic beetles (Hydroporus spp.) and effects on offspring life‐history
Authors: BRODIN TOMAS , JOHANSSON FRANK , BERGSTEN JOHANNES
Published: June 2006

1. Theory predicts that natural selection should favour females that are able to correctly assess the risk of predation and then use that information to avoid high‐risk oviposition sites to reduce the risk of offspring predation. Despite the potential significance of such behaviour on individual fitness, population dynamics and community structure, relatively few studies of oviposition behaviour connected to the risk of predation have been carried out.

2. However, some recent studies suggest that oviposition site selection in response to risk of predation may be a common phenomenon, at least among amphibians and mosquitoes. A vast majority of previous studies have, however, neglected to investigate how the offspring are affected, in terms of fitness related parameters, by the maternal oviposition site choice.

3. In an outdoor artificial pond experiment we tested the oviposition site selection of female aquatic beetles (Hydroporus spp.) in relation to the presence or absence of a predatory fish (Perca fluviatilis). In addition, we monitored how the oviposition site selection affected the behaviour, growth and food resource of the progeny.

4. We show that free‐flying females of the aquatic beetles Hydroporus incognitus and H. nigrita prefer to oviposit in waters without fish compared with waters with fish. Larval activity of Hydroporus spp. was unaffected by fish presence. Our results indicate that beetle larvae from females that do lay eggs in waters with fish show increased growth compared with larvae in waters without fish. We explain this difference in growth by a higher per‐capita food supply in the presence of a fish predator. This finding may have important implications for our understanding of how the variance of oviposition site selection in a population is sustained.
Extracellular phosphatases in a Mediterranean reservoir: seasonal, spatial and kinetic heterogeneity
Authors: NEDOMA J. , GARCÍA J. C. , COMERMA M. , ŠIMEK K. , ARMENGOL J.
Published: June 2006

1. Epilimnetic alkaline phosphatase activity (APA) was measured in longitudinal profiles of the canyon‐shaped, eutrophic Sau Reservoir (Catalonia, Spain) during the autumn, winter and spring periods of 1997–2000.

2. The spatial pattern of APA depended on lake circulation. During periods of stable stratification, when the ratio of mixed to euphotic depth (zmix/zeu < 1.7) was low and the Chlorophyll a (Chl a) concentration high, APA was also comparatively high (0.5–3.4 μmol L−1 h−1) and located mostly in the >2‐μm size‐fraction. APA increased towards the dam at the same time as the concentration of soluble reactive phosphorus (SRP) decreased. In periods of unstable stratification, deep mixing (zmix/zeu > 2.4) and low Chl a concentration, APA was low (<0.1 μmol L−1 h−1) and without longitudinal changes, consistent with a high and stable SRP concentration.

3. A high input of mostly dissolved (in the <0.2‐μm size‐fraction) phosphatases from the river Ter was found in 1997–98. At the river inflow, independently of season and despite a continuously high SRP concentration, APA was approximately 0.7 μmol L−1 h−1 and decreased towards the dam within the inflowing, canyon‐like part of the reservoir.

4. Analysis of saturation kinetics revealed the kinetic heterogeneity of APA. Low‐affinity APA was localised in the >2‐μm (algal) size‐fraction while, in the <2‐μm (picoplankton, mainly bacteria + dissolved) size‐fraction, high‐affinity APA, or a mixture of both, was found. The presence of two kinetic components, whose substrate affinities (i.e. in Michaelis constants, Km) differed, was confirmed statistically in 13 of 18 cases analysed. The range of KmH values of the high‐affinity component was 0.15–2.4 μmol L−1, KmL values of the low‐affinity component ranged from 18 to 275 μmol L−1.
The initiator caspase, caspase‐10β, and the BH‐3‐only molecule, Bid, demonstrate evolutionary conservation in Xenopus of their pro‐apoptotic activities in the extrinsic and intrinsic pathways
Authors: Kominami Katsuya , Takagi Chiyo , Kurata Tomoko , Kitayama Atsushi , Nozaki Masami , Sawasaki Tatsuya , Kuida Keisuke , Endo Yaeta , Manabe Noboru , Ueno Naoto , Sakamaki Kazuhiro
Published: June 2006

Two major apoptotic signaling pathways have been defined in mammals, the extrinsic pathway, initiated by ligation of death receptors, and the intrinsic pathway, triggered by cytochrome c release from mitochondria. Here, we identified and characterized the Xenopus homologs of caspase‐10 (xCaspase‐10β), a novel initiator caspase, and Bid (xBid), a BH3‐only molecule of the Bcl‐2 family involved in both the extrinsic and intrinsic pathways. Exogenous expression of these molecules induced apoptosis of mammalian cells. By biochemical and cytological analyses, we clarified that xCaspase‐10β and xBid exhibit structural and functional similarities to their mammalian orthologues. We also detected xCaspase‐10β and xBid transcripts during embryogenesis by whole‐mount in situ hybridization and RT‐PCR analysis. Microinjection of mRNA encoding a protease‐defect xCaspase‐10β mutant into embryos resulted in irregular development. Enforced expression of active xBid induced cell death in developing embryos. Using transgenic frogs established to allow monitoring of caspase activation in vivo, we confirmed that this form of cell death is caspase‐dependent apoptosis. Thus, we demonstrated that the machinery governing the extrinsic and intrinsic apoptotic pathways are already established in Xenopus embryos. Additionally, we propose that the functions of the initiator caspase and BH3‐only molecule are evolutionarily conserved in vertebrates, functioning during embryonic development.
Forest ecosystems of an ArizonaPinus ponderosalandscape: multifactor classification and implications for ecological restoration
Authors: Abella Scott R. , Covington W. Wallace
Published: June 2006

Aim We developed an ecosystem classification within a 110,000‐ha ArizonaPinus ponderosaP. & C. Lawson (ponderosa pine) landscape to support ecological restoration of these forests. Specific objectives included identifying key environmental variables constraining ecosystem distribution and comparing plant species composition, richness and tree growth among ecosystems.

Location The Coconino National Forest and the Northern Arizona University Centennial Forest, in northern Arizona, USA.

Methods We sampled geomorphology, soils and vegetation on 66 0.05‐ha plots in open stands containing trees of pre‐settlement (c. 1875) origin, and on 26 plots in dense post‐settlement stands. Using cluster analysis and ordination of vegetation and environment matrices, we classified plots into ecosystem types internally similar in environmental and vegetational characteristics.

Results We identified 10 ecosystem types, ranging from dry, black cinders/Phaceliaecosystems to moist aspen/Lathyrusecosystems. Texture, organic carbon and other soil properties reflecting the effects of parent materials structured ecosystem distribution across the landscape, and geomorphology was locally important. Plant species composition was ecosystem‐specific, with C3Festuca arizonicaVasey (Arizona fescue), for instance, abundant in mesic basalt/Festucaecosystems. MeanP. ponderosadiameter increments ranged from 2.3–4.3 mm year−1across ecosystems in stands of pre‐settlement origin, and the ecosystem classification was robust in dense post‐settlement stands.

Main conclusions Several lines of evidence suggest that although species composition may have been altered since settlement, the same basic ecosystems occurred on this landscape in pre‐settlement forests, providing reference information for ecological restoration. Red cinders/Bahiaecosystems were rare historically and > 30% of their area has been burned by crown fires since 1950, indicating that priority could be given to restoring this ecosystem's remaining mapping units. Ecosystem classifications may be useful as data layers in gap analyses to identify restoration and conservation priorities. Ecosystem turnover occurs at broad extents on this landscape, and restoration must accordingly operate across large areas to encompass ecosystem diversity. By incorporating factors driving ecosystem composition, this ecosystem classification represents a framework for estimating spatial variation in ecological properties, such as species diversity, relevant to ecological restoration.
Long‐term effects of forest fragmentation on Amazonian ant communities
Authors: Vasconcelos Heraldo L. , Vilhena José M. S. , Magnusson William E. , Albernaz Ana L. K. M
Published: June 2006

Aim  To analyse the effects of forest fragmentation on ant communities in an Amazonian landscape that has been fragmented for over a century.

Location  The region surrounding the village of Alter do Chão in the Brazilian Amazonian state of Pará (2°30′ S, 54°57′ W).

Methods  Collection of ants and measurements of tree density were performed along transects established in eight sites in continuous forest and in 24 forest fragments surrounded by savanna vegetation. Data on size, perimeter, and degree of isolation (distance to continuous forest and distance to nearest area of forest > 5 ha) of each fragment were obtained from a georeferenced Landsat image of the study area.

Results  There were significant differences in species richness and composition between fragments and continuous forest, and these differences were not related to intersite variation in vegetation structure (tree density). Fragments supported fewer ant species per plot, and these species tended to represent a nested subset of those found in continuous forests. Fragments had significantly fewer rare species and fewer ant genera. However, fragments and continuous forest had similar numbers of species that also occur in the savanna matrix (i.e. that are not forest specialists). Multiple linear regression analyses indicated that species richness and composition in the fragments are significantly affected by fragment area, but not by fragment shape and degree of isolation. More species were found in larger fragments.

Main conclusions  Forest fragmentation influences the organization of ant communities in Amazonian savanna/forest landscapes. Forest fragments harboured, on average, 85% of the species found in continuous forest. That these fragments, despite their long history of isolation, support a relatively large complement of the species found in continuous forest is surprising, especially given that in some recently fragmented landscapes the proportion of species surviving in the fragments is lower. Differences in inter‐fragment distance and type of matrix between Alter do Chão and these other landscapes may be involved. The fact that fragments at Alter do Chão are surrounded by a natural (rather than an anthropogenic) habitat, and that most of them are less than 300 m from another forest area, may have helped to ameliorate the adverse effects of forest fragmentation.
Historical biogeography of South American freshwater fishes
Authors: Hubert Nicolas , Renno Jean‐François
Published: June 2006

Aim To investigate biogeographical patterns of the obligate freshwater fish order Characiformes.

Location South America.

Methods Parsimony analysis of endemicity, likelihood analysis of congruent geographical distribution, and partition Bremer support were used.

Results Areas of endemism are deduced from parsimony analysis of endemicity, and putative dispersal routes from a separate analysis of discordant patterns of distribution.

Main conclusions Our results demonstrate the occurrence of 11 major areas of endemism and support a preferential eastern–western differentiation of the characiforms in the Amazonian region, contrasting with the southern–northern differentiation of terrestrial organisms. The areas of endemism identified seem to be deeply influenced by the distribution of the emerged land during the 100‐m marine highstand that occurred during the late Miocene and allow us to hypothesize the existence of eight aquatic freshwater refuges at that time. The raw distribution of non‐endemic species supports nine patterns of species distribution across the 11 areas of endemism, two of which support a southern–northern differentiation in the eastern part of the Amazon. This result shows that the main channel of the Amazon limited dispersal between tributaries from each bank of the river. The levels of endemism further demonstrate that the aquatic freshwater refuges promoted allopatric speciation and later allowed the colonization of the lowlands. By contrast, the biogeographical pattern found in the western part of the Amazon is identified as a result of the Miocene Andean foreland dynamic and the uplift of the palaeoarches that promoted allopatric divergence across several sedimentary basins by the establishment of disconnected floodplains. The assessment of conflicting species distributions also shows the presence of seven putative dispersal routes between the Amazon, Orinoco and Paraná rivers. Our findings suggest that, rather than there being a single predominant process, the establishment of the modern South American freshwater fish biotas is the result of an interaction between marine incursions, uplift of the palaeoarches, and historical connections allowing cross‐drainage dispersal.
Does specialty board certification influence clinical outcomes?
Authors: Grosch Eric N.
Published: June 2006

Background  The public seems to crave a simplistic index of ‘quality’, analogous to ‘The Good Housekeeping Seal of Approval’, for the complex endeavour of clinical medicine. The American Board of Medical Specialties (ABMS) and its member boards have purported to fill the vacuum in an effort that bears many of the earmarks of a public relations publicity campaign. The author examined the validity of the evidence touted in support of that effort.

Methods  By applying Hill’s causal epidemiologic criteria and logical and statistical inference, the author evaluated: (i) published data sources consisting of the most comprehensive collection of studies yet gathered that purports to provide evidence of the relevance of board certification to clinical outcomes, a collection presented by Sharp et al. apparently with the advice and consent of ABMS, that they posited as containing ‘relevant findings’, to what purpose they left unspecified; and (ii) the review article of Sharp et al.

Results  The data that Sharp et al. presented provided no credible link between specialty board certification and outcomes or ‘quality’ of clinical care. Sharp et al. ignored the evidence of absent evidence they found and proposed enthusiastic but unjustified conclusions in support of specialty board certification as an index of clinical ‘expertise’.

Conclusions  No evidence supports the touted clinical benefit of specialty board certification. Specialists in clinical medicine and surgery are unamenable to simplistic evaluation by examination, yet specialty board certification remains an ersatz standard of doctors’ clinical quality in the absence of supporting evidence.
A comparison between insertion torque and resonance frequency in the assessment of torque capacity and primary stability of Brånemark system implants
Authors: TURKYILMAZ I.
Published: June 2006

summary  The aim of this study was to determine primary stability and insertion torque of Brånemark System implants placed in the anterior mandible, and to evaluate a possible correlation between primary stability and insertion torque. Thirty edentulous patients were treated with 60 Brånemark System implants using a one‐stage technique. The insertion torque values of all implants were recorded with the Osseocare equipment. Immediately after implant placement, each implant was connected to the transducer of an Osstell machine to measure the primary implant stability. The average insertion torque and resonance frequency values were 41·5 ± 5·8 and 74·1 ± 3·8 for 30 implants. The correlation between insertion torque and resonance frequency values indicated a statistical significance (P < 0·001). The difference between mean insertion torque values for female and male patients was statistically significant (P < 0·001). No significant difference (P > 0·05) was found between younger and older patients with mean insertion torque values of 43·1 ± 4·7 and 40·1 ± 6·5 respectively. The results of this study showed a strong correlation between the primary stability and insertion torque values of Brånemark System TiUnite MKIII implants at the time of implant placement.
Prosthetic complications in fixed endosseous implant‐borne reconstructions after an observations period of at least 40 months
Authors: DE BOEVER A. L. , KEERSMAEKERS K. , VANMAELE G. , KERSCHBAUM T. , THEUNIERS G. , DE BOEVER J. A.
Published: June 2006

summary  One hundred and seventy‐two fixed reconstructions (317 prosthetic units), made on 283 ITI implants in 105 patients (age range 25–86 years) with a minimum follow‐up period of 40 months, were taken into the study to analyse technical complication rate, complication type and costs for repair. The mean evaluation time was 62·5 ± 25·3 months. Eighty were single crowns and 92 different types of fixed partial dentures (FPDs). In 45 cases the construction was screw retained and in 127 cases cemented with zinc phosphate cement or an acrylic‐based cement. Complications occurred after a minimum period of 2 months and a maximum period of 100 months (mean: 35·9 ± 21·4 months). Fifty‐five prosthetic interventions were needed on 44 constructions (25%) of which 88% in the molar/premolar region. The lowest percentage of complications occurred in single crowns (25%), the highest in 3–4 unit FPDs (35%) and in FPDs with an extension (44%). Of the necessary clinical repair, 36% was recementing and 38% tightening the screws. Of all interventions, 14% were classified as minor (no treatment or <10 min chair time), 70% as moderate (>10 min but <60 min chair time) and 14% as major interventions (>60 min and additional costs for replacement of parts and/or laboratory). For seven patients the additional costs ranged from €28 to €840. Bruxing seemed to play a significant role in the frequency of complications. Longer constructions seemed to be more prone to complications. The relatively high occurrence of technical complications should be discussed with the patient before the start of the treatment.
Effect of implant support on distal extension removable partial dentures: in vitro assessment
Authors: OHKUBO C. , KURIHARA D. , SHIMPO H. , SUZUKI Y. , KOKUBO Y. , HOSOI T.
Published: June 2006

summary  The implants in implant‐supported removable partial dentures (RPDs) are placed in the edentulous ridge to stabilize the RPD and minimize the resultant rotational movement. This study investigated the effect of implant placement on RPD stability. A model simulating a mandibular bilateral distal extension missing was fabricated using epoxy resin and silicone impression material as thin (1 mm) and thick (2 mm) soft tissues. Five pressure sensors (PS‐10K, Kyowa, Tokyo, Japan) were attached near the left and right first molars (#36 and #46), first premolars (#34 and #44) and medio‐lingual alveolar crest. Five bilateral distal extension RPDs with Co–Cr frameworks were conventionally fabricated. After the implants were placed at the bilateral second molar areas, healing caps (4·5 mm high) were connected to the denture base with autopolymerized resin to support the RPD. As in a conventional RPD, sealing screws were placed without connecting them. Loads up to 5 kg were applied, and the pressure and displacement of the RPDs (n = 5) were simultaneously measured and analysed using the Wilcoxen test (α = 0·05). There was less pressure on both thin and thick soft tissues, the #36, #46 and the medio‐lingual alveolar crest from the implant‐supported RPD than from the conventional RPD (P < 0·05). There were no significant differences in pressure on #34 and #44 between the two RPDs (P > 0·05). There was significantly less denture displacement of the implant‐supported RPD than of the conventional denture (P < 0·05). Implant support helped prevent the displacement of distal extension RPDs and decreased the pressure on soft tissues.
Surface anchoring of a bacterial adhesin secreted by the two‐partner secretion pathway
Authors: Buscher Amy Z. , Grass Susan , Heuser John , Roth Robyn , St. Geme Joseph W.
Published: June 2006

In Gram‐negative bacteria, most surface‐associated proteins are present as integral outer‐membrane proteins. Exceptions include the Haemophilus influenzae HMW1 and HMW2 adhesins and a subset of other proteins secreted by the two‐partner secretion system. In the present study we sought to determine the mechanism by which HMW1 is anchored to the bacterial surface. In initial experiments we found that HMW1 forms hair‐like fibres on the bacterial surface and is usually present as pairs that appear to be joined together at one end. Further analysis established that HMW1 is anchored to the multimeric HMW1B outer membrane translocator, resulting in a direct correlation between the level of surface‐associated HMW1 and the quantity of HMW1B in the outer membrane. Mutagenesis and polyethylene glycol maleimide labelling revealed that anchoring of HMW1 requires the C‐terminal 20 amino acids of the protein and is dependent upon disulphide bond formation between two conserved cysteine residues in this region. Immunolabelling studies demonstrated that the immediate C‐terminus of HMW1 is inaccessible to surface labelling, suggesting that it remains in the periplasm or is buried in HMW1B. Coexpression of HMW1 lacking the C‐terminal 20 amino acids and wild‐type HMW1 supported the conclusion that the C‐terminus of HMW1 occupies the HMW1B pore. These observations may have broad relevance to proteins secreted by the two‐partner secretion system, especially given the conservation of C‐terminal cysteine residues among surface‐associated proteins in this family.
A lesson in efficient killing from two‐component lantibiotics
Authors: Breukink Eefjan
Published: June 2006

The combined activity of the constituents of two‐component antibiotic systems is always significantly higher than the sum of the activities of the individual pieces. Understanding the principles behind this phenomenon might provide new ways to design new antibiotics. In this issue of Molecular Microbiology, Wiedemann and coworkers have made a big step towards understanding the mechanism of action of the two‐component lanthionine‐containing antibiotic lacticin 3147. It has now become clear that this two‐component system specifically targets the bacterial cell wall precursor Lipid II. This makes this essential bacterial lipid one of the most sought‐after targets in nature. Surprisingly, in view of its small size (MW 1875 Da), this is now the fifth different way that this key molecule is known to be targeted.
Progressive segregation of the Escherichia coli chromosome
Authors: Nielsen Henrik J. , Li Yongfang , Youngren Brenda , Hansen Flemming G. , Austin Stuart
Published: June 2006

We have followed the fate of 14 different loci around the Escherichia coli chromosome in living cells at slow growth rate using a highly efficient labelling system and automated measurements. Loci are segregated as they are replicated, but with a marked delay. Most markers segregate in a smooth temporal progression from origin to terminus. Thus, the overall pattern is one of continuous segregation during replication and is not consistent with recently published models invoking extensive sister chromosome cohesion followed by simultaneous segregation of the bulk of the chromosome. The terminus, and a region immediately clockwise from the origin, are exceptions to the overall pattern and are subjected to a more extensive delay prior to segregation. The origin region and nearby loci are replicated and segregated from the cell centre, later markers from the various positions where they lie in the nucleoid, and the terminus region from the cell centre. Segregation appears to leave one copy of each locus in place, and rapidly transport the other to the other side of the cell centre.
Assessment of oesophageal emptying in achalasia patients by intraluminal impedance monitoring
Authors: CONCHILLO J. M. , SELIMAH M. , BREDENOORD A. J. , SAMSOM M. , SMOUT A. J. P. M.
Published: June 2006

Abstract  Oesophageal emptying can be assessed by radiographic and scintigraphic tests with radiation exposure or by multichannel intraluminal impedance monitoring (MII). The aim of this study was to evaluate the applicability of MII for the assessment of oesophageal emptying in achalasia patients. In 10 achalasia patients, impedance tracings were scored independently by three observers after ingestion of a 100‐mL barium bolus. Bolus clearance time (BCT) and height of barium column were scored using fluoroscopic images acquired at 20‐s intervals. All patients showed a low baseline impedance level in the distal oesophagus. Air trapping in the proximal oesophagus was detected in nine patients. BCT on MII was similar to that on fluoroscopy in 40–70% of the patients. Correlations between height of barium on fluoroscopy and fluid level on MII were poor to moderate at different time intervals. Concordance (Kendall's coefficient) between the three observers for assessment of fluid level on MII was 0.31 (P = 0.04) at 1 and 5 min, 0.26 (P = 0.08) at 10 and 0.44 (P = 0.01) at 15 min. We conclude that in achalasia patients, low baseline impedance levels and air entrapment in the proximal oesophagus limit the value of intraluminal impedance monitoring as a test of oesophageal emptying.