bluuebunny/crossref_metadata_2025 huggingface dataset:
The dynamics of intergenerational sexual relationships: the experience of schoolgirls in Botswana
Authors: Nkosana Josephine , Rosenthal Doreen
Published: August 2007

Background: Studies conducted in several sub-Saharan African countries have revealed that women and girls engage in intergenerational sexual relationships without the protection of condoms, giving cause for concern about HIV transmission. These relationships often occur against the girls’ will and for many reasons, including reasons associated with subsistence. However, some young women do act as active social agents who rationally engage in intergenerational sexual exchanges oriented towards consumption. The present study examines the dynamics of intergenerational sexual relationships among schoolgirls in Botswana. Methods: In-depth interviews were conducted with 15 schoolgirls who were currently in an intergenerational sexual relationship. The social, cultural and economic factors that cause young girls to engage in these relationships and how intergenerational sex contributes to unsafe sexual practices were examined. Results: The findings revealed that not all girls were passive and controlled by their older sexual partners. Some derived pleasure, enjoyment, love and equal partnership in these sexual relationships. They displayed a capacity to take charge of their own sexual lives by insisting on and engaging in safe-sex behaviours. Another set of girls had little or no decision-making power. Their relationships with older boyfriends were characterised by coercion and manipulation. Negotiation for condom use was difficult for this group. Conclusions: Effective policy and practice can be informed by the findings, leading to a reduction in HIV transmission as a result of intergenerational sex. In particular, the study has drawn attention to girls who are able to assert themselves within intergenerational sexual relationships and successfully negotiate safe sex. These strategies can be incorporated in programs to assist girls who face challenges and difficulties in negotiating safe sex with older men.
A new surveillance system for monitoring HIV infection in Victoria, Australia
Authors: Guy Rebecca , Lim Megan S. C. , Wang Yung-Hsuan J. , Medland Nicholas , Anderson Jonathan , Roth Norman , Hellard Margaret E.
Published: August 2007

Objectives: To establish a new mechanism for monitoring patterns of HIV infection, in the context of a sustained increase in HIV diagnosis among men who have sex with men (MSM) in Victoria. Methods: Between April 2004 and August 2005, a linked voluntary HIV sentinel surveillance system was implemented at five medical clinics with a high case load of MSM. Using a questionnaire, doctors collected HIV testing history, demographic and sexual risk behaviour information from all clients undergoing voluntary HIV testing. Questionnaires were linked with HIV test results. Logistic regression analysis was conducted to determine factors associated with HIV infection. Results: Of 3435 MSM tested for HIV at participating sites, 1.7%, (95% CI = 1.2–2.2) were newly diagnosed with HIV; between 2004 and 2005 the proportion increased from 1.3% (95% CI = 1.2–1.5) to 2.0% (95% CI = 1.8–2.2), P = 0.107. There was no significant change in the number of HIV tests conducted per month or in demographic characteristics, testing history and sexual behaviour characteristics between time periods. In multivariate analysis, reporting unprotected anal intercourse (UAI) with any partner, UAI with a HIV-positive partner/s and being aged 30–39 years or 40 years or greater were significantly associated with HIV infection. Conclusion: This new surveillance mechanism, based on linked testing at participating clinics, indicates that the increase in HIV notifications in 2005 was unrelated to changes in testing and data from a Melbourne sexual behavioural survey suggests the increase was more likely to be attributed to increases in transmission within the past few years. The sentinel system highlighted UAI, especially with HIV positive partner/s are important transmission factors.
Transgender people attending a Sydney sexual health service over a 16-year period
Authors: Hounsfield Victoria L. , Freedman Eleanor , McNulty Anna , Bourne Christopher
Published: August 2007

Background: Previous studies have concluded that transgender people are a marginalised and stigmatised group, with high rates of sexually transmissible infections (STI), sex work, injecting drug use and multiple sexual partners. To our knowledge, this is the first study in Australia to focus on the sexual behaviour and sexual health needs of transgender people attending an urban sexual health clinic. Methods: A retrospective case note review was undertaken of the transgender attendees of the Sydney Sexual Health Centre between 1990 and 2006. Demographics, gender characteristics, risk behaviours, sexual health morbidity, psychosocial information and other significant features of the transgender population were assessed. Results: Forty clients were identified as transgender, of whom 36 (90%) were male-to-female and four (10%) were female-to-male. Seventeen (43%) had a history of sex work, 16 (40%) had injected drugs, 14 (35%) had had unprotected anal or vaginal sex in the past 3 months. Twenty (50%) clients had histories of a STI, including three (7.5%) that were HIV positive, and two were co-infected with hepatitis C. Genital warts and chlamydia were the most common diagnoses made during the study period. Physical examination was inadequately documented in 53% of first visits. Psychosocial morbidity was common. Conclusions: Transgender clients presented infrequently at this clinic. Although half reported few risks, the other half reported multiple risk behaviours and had most STI. These findings suggest that there needs to be improved sexual health service for transgender clients at our clinic.
Rap1-PDZ-GEF1 interacts with a neurotrophin receptor at late endosomes, leading to sustained activation of Rap1 and ERK and neurite outgrowth
Authors: Hisata Shu , Sakisaka Toshiaki , Baba Takeshi , Yamada Tomohiro , Aoki Kazuhiro , Matsuda Michiyuki , Takai Yoshimi
Published: August 2007

Neurotrophins, such as NGF and BDNF, induce sustained activation of Rap1 small G protein and ERK, which are essential for neurite outgrowth. We show involvement of a GDP/GTP exchange factor (GEF) for Rap1, PDZ-GEF1, in these processes. PDZ-GEF1 is activated by GTP-Rap1 via a positive feedback mechanism. Upon NGF binding, the TrkA neurotrophin receptor is internalized from the cell surface, passes through early endosomes, and arrives in late endosomes. A tetrameric complex forms between PDZ-GEF1, synaptic scaffolding molecule and ankyrin repeat-rich membrane spanning protein which interacts directly with the TrkA receptor. At late endosomes, the complex induces sustained activation of Rap1 and ERK, resulting in neurite outgrowth. In cultured rat hippocampal neurons, PDZ-GEF1 is recruited to late endosomes in a BDNF-dependent manner involved in BDNF-induced neurite outgrowth. Thus, the interaction of PDZ-GEF1 with an internalized neurotrophin receptor transported to late endosomes induces sustained activation of both Rap1 and ERK and neurite outgrowth.
Three-dimensional arrangement of F-actin in the contractile ring of fission yeast
Authors: Kamasaki Tomoko , Osumi Masako , Mabuchi Issei
Published: August 2007

The contractile ring, which is required for cytokinesis in animal and yeast cells, consists mainly of actin filaments. Here, we investigate the directionality of the filaments in fission yeast using myosin S1 decoration and electron microscopy. The contractile ring is composed of around 1,000 to 2,000 filaments each around 0.6 μm in length. During the early stages of cytokinesis, the ring consists of two semicircular populations of parallel filaments of opposite directionality. At later stages, before contraction, the ring filaments show mixed directionality. We consider that the ring is initially assembled from a single site in the division plane and that filaments subsequently rearrange before contraction initiates.
The yeast integral membrane protein Apq12 potentially links membrane dynamics to assembly of nuclear pore complexes
Authors: Scarcelli John J. , Hodge Christine A. , Cole Charles N.
Published: August 2007

Although the structure and function of components of the nuclear pore complex (NPC) have been the focus of many studies, relatively little is known about NPC biogenesis. In this study, we report that Apq12 is required for efficient NPC biogenesis in Saccharomyces cerevisiae. Apq12 is an integral membrane protein of the nuclear envelope (NE) and endoplasmic reticulum. Cells lacking Apq12 are cold sensitive for growth, and a subset of their nucleoporins (Nups), those that are primarily components of the cytoplasmic fibrils of the NPC, mislocalize to the cytoplasm. APQ12 deletion also causes defects in NE morphology. In the absence of Apq12, most NPCs appear to be associated with the inner but not the outer nuclear membrane. Low levels of benzyl alcohol, which increases membrane fluidity, prevented Nup mislocalization and restored the proper localization of Nups that had accumulated in cytoplasmic foci upon a shift to lower temperature. Thus, Apq12p connects nuclear pore biogenesis to the dynamics of the NE.
A nuclear envelope protein linking nuclear pore basket assembly, SUMO protease regulation, and mRNA surveillance
Authors: Lewis Alaron , Felberbaum Rachael , Hochstrasser Mark
Published: August 2007

The nuclear pore complex (NPC) is both the major conduit for nucleocytoplasmic trafficking and a platform for organizing macromolecules at the nuclear envelope. We report that yeast Esc1, a non-NPC nuclear envelope protein, is required both for proper assembly of the nuclear basket, a structure extending into the nucleus from the NPC, and for normal NPC localization of the Ulp1 SUMO protease. In esc1Δ cells, Ulp1 and nuclear basket components Nup60 and Mlp1 no longer distribute broadly around the nuclear periphery, but co-localize in a small number of dense-staining perinuclear foci. Loss of Esc1 (or Nup60) alters SUMO conjugate accumulation and enhances ulp1 mutant defects. Similar to previous findings with Mlp1, both Esc1 and Ulp1 help retain unspliced pre-mRNAs in the nucleus. Therefore, these proteins are essential for proper nuclear basket function, which includes mRNA surveillance and regulation of SUMO protein dynamics. The results raise the possibility that NPC-localized protein desumoylation may be a key regulatory event preventing inappropriate pre-mRNA export.
Functional association of Sun1 with nuclear pore complexes
Authors: Liu Qian , Pante Nelly , Misteli Tom , Elsagga Mohamed , Crisp Melissa , Hodzic Didier , Burke Brian , Roux Kyle J.
Published: August 2007

Sun1 and 2 are A-type lamin-binding proteins that, in association with nesprins, form a link between the inner nuclear membranes (INMs) and outer nuclear membranes of mammalian nuclear envelopes. Both immunofluorescence and immunoelectron microscopy reveal that Sun1 but not Sun2 is intimately associated with nuclear pore complexes (NPCs). Topological analyses indicate that Sun1 is a type II integral protein of the INM. Localization of Sun1 to the INM is defined by at least two discrete regions within its nucleoplasmic domain. However, association with NPCs is dependent on the synergy of both nucleoplasmic and lumenal domains. Cells that are either depleted of Sun1 by RNA interference or that overexpress dominant-negative Sun1 fragments exhibit clustering of NPCs. The implication is that Sun1 represents an important determinant of NPC distribution across the nuclear surface.
Deletion of tumor necrosis factor death receptor inhibits amyloid β generation and prevents learning and memory deficits in Alzheimer's mice
Authors: He Ping , Zhong Zhenyu , Lindholm Kristina , Berning Lilian , Lee Wendy , Lemere Cynthia , Staufenbiel Matthias , Li Rena , Shen Yong
Published: August 2007

The tumor necrosis factor type 1 death receptor (TNFR1) contributes to apoptosis. TNFR1, a subgroup of the TNFR superfamily, contains a cytoplasmic death domain. We recently demonstrated that the TNFR1 cascade is required for amyloid β protein (Aβ)–induced neuronal death. However, the function of TNFR1 in Aβ plaque pathology and amyloid precursor protein (APP) processing in Alzheimer's disease (AD) remains unclear. We report that the deletion of the TNFR1 gene in APP23 transgenic mice (APP23/TNFR1−/−) inhibits Aβ generation and diminishes Aβ plaque formation in the brain. Genetic deletion of TNFR1 leads to reduced β-secretase 1 (BACE1) levels and activity. TNFR1 regulates BACE1 promoter activity via the nuclear factor-κB pathway, and the deletion of TNFR1 in APP23 transgenic mice prevents learning and memory deficits. These findings suggest that TNFR1 not only contributes to neurodegeneration but also that it is involved in APP processing and Aβ plaque formation. Thus, TNFR1 is a novel therapeutic target for AD.
Nectin-like proteins mediate axon–Schwann cell interactions along the internode and are essential for myelination
Authors: Maurel Patrice , Einheber Steven , Galinska Jolanta , Thaker Pratik , Lam Isabel , Rubin Marina B. , Scherer Steven S. , Murakami Yoshinuri , Gutmann David H. , Salzer James L.
Published: August 2007

Axon–glial interactions are critical for the induction of myelination and the domain organization of myelinated fibers. Although molecular complexes that mediate these interactions in the nodal region are known, their counterparts along the internode are poorly defined. We report that neurons and Schwann cells express distinct sets of nectin-like (Necl) proteins: axons highly express Necl-1 and -2, whereas Schwann cells express Necl-4 and lower amounts of Necl-2. These proteins are strikingly localized to the internode, where Necl-1 and -2 on the axon are directly apposed by Necl-4 on the Schwann cell; all three proteins are also enriched at Schmidt-Lanterman incisures. Binding experiments demonstrate that the Necl proteins preferentially mediate heterophilic rather than homophilic interactions. In particular, Necl-1 on axons binds specifically to Necl-4 on Schwann cells. Knockdown of Necl-4 by short hairpin RNA inhibits Schwann cell differentiation and subsequent myelination in cocultures. These results demonstrate a key role for Necl-4 in initiating peripheral nervous system myelination and implicate the Necl proteins as mediators of axo–glial interactions along the internode.
Putting the glue in glia: Necls mediate Schwann cell–axon adhesion
Authors: Perlin Julie R. , Talbot William S.
Published: August 2007

Interactions between Schwann cells and axons are critical for the development and function of myelinated axons. Two recent studies (see Maurel et al. on p. 861 of this issue; Spiegel et al., 2007) report that the nectin-like (Necl) proteins Necl-1 and -4 are internodal adhesion molecules that are critical for myelination. These studies suggest that Necl proteins mediate a specific interaction between Schwann cells and axons that allows proper communication of the signals that trigger myelination.
Simulation of Ca2+ Movements within the Sarcomere of Fast-Twitch Mouse Fibers Stimulated by Action Potentials
Authors: Baylor Stephen M. , Hollingworth Stephen
Published: August 2007

Ca2+ release from the sarcoplasmic reticulum (SR) of skeletal muscle takes place at the triadic junctions; following release, Ca2+ spreads within the sarcomere by diffusion. Here, we report multicompartment simulations of changes in sarcomeric Ca2+ evoked by action potentials (APs) in fast-twitch fibers of adult mice. The simulations include Ca2+ complexation reactions with ATP, troponin, parvalbumin, and the SR Ca2+ pump, as well as Ca2+ transport by the pump. Results are compared with spatially averaged Ca2+ transients measured in mouse fibers with furaptra, a low-affinity, rapidly responding Ca2+ indicator. The furaptra ΔfCaD signal (change in the fraction of the indicator in the Ca2+-bound form) evoked by one AP is well simulated under the assumption that SR Ca2+ release has a peak of 200–225 μM/ms and a FDHM of ∼1.6 ms (16°C). ΔfCaD elicited by a five-shock, 67-Hz train of APs is well simulated under the assumption that in response to APs 2–5, Ca2+ release decreases progressively from 0.25 to 0.15 times that elicited by the first AP, a reduction likely due to Ca2+ inactivation of Ca2+ release. Recovery from inactivation was studied with a two-AP protocol; the amplitude of the second release recovered to >0.9 times that of the first with a rate constant of 7 s−1. An obvious feature of ΔfCaD during a five-shock train is a progressive decline in the rate of decay from the individual peaks of ΔfCaD. According to the simulations, this decline is due to a reduction in available Ca2+ binding sites on troponin and parvalbumin. The effects of sarcomere length, the location of the triadic junctions, resting [Ca2+], the parvalbumin concentration, and possible uptake of Ca2+ by mitochondria were also investigated. Overall, the simulations indicate that this reaction-diffusion model, which was originally developed for Ca2+ sparks in frog fibers, works well when adapted to mouse fast-twitch fibers stimulated by APs.
Martin points on open manifolds of non-positive curvature
Authors: Cao Jianguo , Fan Huijun , Ledrappier François
Published: August 2007

The Martin boundary of a Cartan-Hadamard manifold describes a fine geometric structure at infinity, which is a sub-space of positive harmonic functions. We describe conditions which ensure that some points of the sphere at infinity belong to the Martin boundary as well. In the case of the universal cover of a compact manifold with Ballmann rank one, we show that Martin points are generic and of full harmonic measure. The result of this paper provides a partial answer to an open problem of S. T. Yau.
Surjectivity for Hamiltonian 𝐺-spaces in 𝐾-theory
Authors: Harada Megumi , Landweber Gregory
Published: August 2007

Let

G
G

be a compact connected Lie group, and

(
M
,
ω
)

(M,\omega )

a Hamiltonian

G
G

-space with proper moment map

μ
\mu

. We give a surjectivity result which expresses the

K
K

-theory of the symplectic quotient

M

/

/

G

M /\!\!/G

in terms of the equivariant

K
K

-theory of the original manifold

M
M

, under certain technical conditions on

μ
\mu

. This result is a natural

K
K

-theoretic analogue of the Kirwan surjectivity theorem in symplectic geometry. The main technical tool is the

K
K

-theoretic Atiyah-Bott lemma, which plays a fundamental role in the symplectic geometry of Hamiltonian

G
G

-spaces. We discuss this lemma in detail and highlight the differences between the

K
K

-theory and rational cohomology versions of this lemma. We also introduce a

K
K

-theoretic version of equivariant formality and prove that when the fundamental group of

G
G

is torsion-free, every compact Hamiltonian

G
G

-space is equivariantly formal. Under these conditions, the forgetful map

K

G

∗

(
M
)
→

K

∗

(
M
)

K_{G}^{*}(M)\to K^{*}(M)

is surjective, and thus every complex vector bundle admits a stable equivariant structure. Furthermore, by considering complex line bundles, we show that every integral cohomology class in

H

2

(
M
;

Z

)

H^{2}(M;\mathbb {Z})

admits an equivariant extension in

H

G

2

(
M
;

Z

)

H_{G}^{2}(M;\mathbb {Z})

.
The divergence theorem for unbounded vector fields
Authors: De Pauw Thierry , Pfeffer Washek
Published: August 2007

In the context of Lebesgue integration, we derive the divergence theorem for unbounded vector fields that can have singularities at every point of a compact set whose Minkowski content of codimension greater than two is finite. The resulting integration by parts theorem is applied to removable sets of holomorphic and harmonic functions.
Quotients of standard Hilbert modules
Authors: Arveson William
Published: August 2007

We initiate a study of Hilbert modules over the polynomial algebra

A

=

C

[

z
1

,
…
,

z
d

]

\mathcal A=\mathbb C[z_1,\dots ,z_d]

that are obtained by completing

A

\mathcal A

with respect to an inner product having certain natural properties. A standard Hilbert module is a finite multiplicity version of one of these. Standard Hilbert modules occupy a position analogous to that of free modules of finite rank in commutative algebra, and their quotients by submodules give rise to universal solutions of nonlinear relations. Essentially all of the basic Hilbert modules that have received attention over the years are standard, including the Hilbert module of the

d
d

-shift, the Hardy and Bergman modules of the unit ball, modules associated with more general domains in

C

d

\mathbb C^d

, and those associated with projective algebraic varieties. We address the general problem of determining when a quotient

H

/

M

H/M

of an essentially normal standard Hilbert module

H
H

is essentially normal. This problem has been resistant. Our main result is that it can be “linearized” in that the nonlinear relations defining the submodule

M
M

can be reduced, appropriately, to linear relations through an iteration procedure, and we give a concrete description of linearized quotients.
On 𝑝-adic intermediate Jacobians
Authors: Raskind Wayne , Xarles Xavier
Published: August 2007

For an algebraic variety

X
X

of dimension

d
d

with totally degenerate reduction over a

p
p

-adic field (definition recalled below) and an integer

i
i

with

1
≤
i
≤
d

1\leq i\leq d

, we define a rigid analytic torus

J
i

(
X
)

J^i(X)

together with an Abel-Jacobi mapping to it from the Chow group

C

H
i

(
X

)

h
o
m

CH^i(X)_{hom}

of codimension

i
i

algebraic cycles that are homologically equivalent to zero modulo rational equivalence. These tori are analogous to those defined by Griffiths using Hodge theory over

C

\bf {C}

. We compare and contrast the complex and

p
p

-adic theories. Finally, we examine a special case of a

p
p

-adic analogue of the Generalized Hodge Conjecture.
The distance function from the boundary in a Minkowski space
Authors: Crasta Graziano , Malusa Annalisa
Published: August 2007

Let the space

R

n

\mathbb R^n

be endowed with a Minkowski structure

M
M

(that is,

M
:

R

n

→
[
0
,
+
∞
)

M\colon \mathbb R^n \to [0,+\infty )

is the gauge function of a compact convex set having the origin as an interior point, and with boundary of class

C
2

C^2

), and let

d
M

(
x
,
y
)

d^M(x,y)

be the (asymmetric) distance associated to

M
M

. Given an open domain

Ω
⊂

R

n

\Omega \subset \mathbb R^n

of class

C
2

C^2

, let
<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" alttext="d Subscript normal upper Omega Baseline left-parenthesis x right-parenthesis colon equals inf left-brace d Superscript upper M Baseline left-parenthesis x comma y right-parenthesis semicolon y element-of partial-differential normal upper Omega right-brace">

d

Ω

(
x
)
:=
inf
{

d
M

(
x
,
y
)
;
 
y
∈
∂
Ω
}

d_{\Omega }(x) := \inf \{d^M(x,y);\ y\in \partial \Omega \}

be the Minkowski distance of a point

x
∈
Ω

x\in \Omega

from the boundary of

Ω
\Omega

. We prove that a suitable extension of

d

Ω

d_{\Omega }

to

R

n

\mathbb R^n

(which plays the rôle of a signed Minkowski distance to

∂
Ω

\partial \Omega

) is of class

C
2

C^2

in a tubular neighborhood of

∂
Ω

\partial \Omega

, and that

d

Ω

d_{\Omega }

is of class

C
2

C^2

outside the cut locus of

∂
Ω

\partial \Omega

(that is, the closure of the set of points of nondifferentiability of

d

Ω

d_{\Omega }

in

Ω
\Omega

). In addition, we prove that the cut locus of

∂
Ω

\partial \Omega

has Lebesgue measure zero, and that

Ω
\Omega

can be decomposed, up to this set of vanishing measure, into geodesics starting from

∂
Ω

\partial \Omega

and going into

Ω
\Omega

along the normal direction (with respect to the Minkowski distance). We compute explicitly the Jacobian determinant of the change of variables that associates to every point

x
∈
Ω

x\in \Omega

outside the cut locus the pair

(
p
(
x
)
,

d

Ω

(
x
)
)

(p(x), d_{\Omega }(x))

, where

p
(
x
)

p(x)

denotes the (unique) projection of

x
x

on

∂
Ω

\partial \Omega

, and we apply these techniques to the analysis of PDEs of Monge–Kantorovich type arising from problems in optimal transportation theory and shape optimization.
A sharp form of the Moser-Trudinger inequality on a compact Riemannian surface
Authors: Yang Yunyan
Published: August 2007

In this paper, a sharp form of the Moser-Trudinger inequality is established on a compact Riemannian surface via the method of blow-up analysis, and the existence of an extremal function for such an inequality is proved.
A single minimal complement for the c.e. degrees
Authors: Lewis Andrew
Published: August 2007

We show that there exists a minimal (Turing) degree

b
>

0
′

b>0’

such that for all non-zero c.e. degrees

a
a

,

0
′

=
a
∨
b

0’=a\vee b

. Since

b
b

is minimal this means that

b
b

complements all c.e. degrees other than

0
0

and

0
′

0’

. Since every

n
n

-c.e. degree bounds a non-zero c.e. degree,

b
b

complements every

n
n

-c.e. degree other than

0
0

and

0
′

0’

.
Quadratic maps and Bockstein closed group extensions
Authors: Pakianathan Jonathan , Yalçın Ergün
Published: August 2007

Let

E
E

be a central extension of the form

0
→
V
→
G
→
W
→
0

0 \to V \to G \to W \to 0

where

V
V

and

W
W

are elementary abelian

2
2

-groups. Associated to

E
E

there is a quadratic map

Q
:
W
→
V

Q: W \to V

, given by the

2
2

-power map, which uniquely determines the extension. This quadratic map also determines the extension class

q
q

of the extension in

H
2

(
W
,
V
)

H^2(W,V)

and an ideal

I
(
q
)

I(q)

in

H
2

(
G
,

Z

/

2
)

H^2(G, \mathbb {Z} /2)

which is generated by the components of

q
q

. We say that

E
E

is Bockstein closed if

I
(
q
)

I(q)

is an ideal closed under the Bockstein operator. We find a direct condition on the quadratic map

Q
Q

that characterizes when the extension is Bockstein closed. Using this characterization, we show for example that quadratic maps induced from the fundamental quadratic map
<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" alttext="upper Q Subscript German g German l Sub Subscript n Subscript Baseline colon German g German l Subscript n Baseline left-parenthesis double-struck upper F 2 right-parenthesis right-arrow German g German l Subscript n Baseline left-parenthesis double-struck upper F 2 right-parenthesis">

Q

g
l

n

:

g
l

n

(

F

2

)
→

g
l

n

(

F

2

)

Q_{\mathfrak {gl}_n}: \mathfrak {gl}_n (\mathbb {F}_2)\to \mathfrak {gl}_n (\mathbb {F}_2)

given by

Q
(

A

)
=

A

+

A

2

Q(\mathbb {A})= \mathbb {A} +\mathbb {A} ^2

yield Bockstein closed extensions. On the other hand, it is well known that an extension is Bockstein closed if and only if it lifts to an extension

0
→
M
→

G
~

→
W
→
0

0 \to M \to \widetilde {G} \to W \to 0

for some

Z

/

4
[
W
]

\mathbb {Z} /4[W]

-lattice

M
M

. In this situation, one may write

β
(
q
)
=
L
q

\beta (q)=Lq

for a “binding matrix”

L
L

with entries in

H
1

(
W
,

Z

/

2
)

H^1(W, \mathbb {Z}/2)

. We find a direct way to calculate the module structure of

M
M

in terms of

L
L

. Using this, we study extensions where the lattice

M
M

is diagonalizable/triangulable and find interesting equivalent conditions to these properties.
LA CHRYSOCOLLE DES ORFEVRES EST‐ELLE JAUNE?
Authors: DEMORTIER G.
Published: August 2007

During the investigation of solders on ancient gold artifacts found in Iran and Syria, cadmium was found at a concentration up to several per cent. Careful interpretation of relative concentrations of copper, silver and cadmium in those solders easily enables discrimination between brazing of modern and ancient origin and forms a simple criterion of identification. Experimental archaeology corroborates this. We suggest a new interpretation of Book XXXIII of Pliny the Elder on the soldering of gold: the chrysocolla of the goldsmith, gold solder, could be greenockite (natural cadmium sulphide) and not necessarily malachite (natural copper carbonate).
PROVENANCE DETERMINATION OF NEOLITHIC TO CLASSICAL MEDITERRANEAN MARBLES BY STABLE ISOTOPES*
Authors: HERZ N.
Published: August 2007

Two stable isotopic data bases for ∂13C and ∂18O values of marble have been accumulated: (1) 590 analyses from 42 Classical quarries of Greece, western Turkey, Tunisia, and Carrara, Italy, and (2) potential Early Bronze Age (EBA) marble sources in the central Cyclades, comprising 192 analyses from 16 sites on the islands of Paros, Naxos, Ios, and Keros. The data bases include the most important marble occurrences in the eastern Mediterranean and so can be used to source artefacts of any age. Neolithic artefacts found at Franchthi Cave, where no marble occurs locally, have been attributed to the Peloponnese and the Cyclades, direct evidence for early trade. In the Cycladic EBA, Naxos and Keros were the principal marble sources for the abundant artefacts found at Keros. The commercial marble trade in Archaic Greece began in the central Cyclades where the tradition apparently went back some 5000 years, to the Neolithic. Classical Greece and especially Rome expanded the number and locations of commercial marble sources throughout the Mediterranean.
Learning disabilities among Nairobi school children
Authors: Dhadphale M. , Ibrahim B.
Published: August 2007

ABSTRACT– Four hundred and forty‐one school children studying in local primary schools were referred during 1980–1981 to the Psychological Assessment Clinic in Nairobi (Kenya) for poor academic performance. The most frequent cause for the learning difficulties of these children was mental retardation. In one third, emotional disorders were responsible for their learning difficulties. Currently, even mentally retarded children are admitted into the existing educational system and are unable to cope. Recommendations for the future are made.
The effect of tardive dyskinesia on body weight
Authors: Yassa R. , Nair N.P.V.
Published: August 2007

ABSTRACT— The effect of tardive dyskinesia (TD) on body weight has been studied longitudinally in 14 subjects suffering from severe TD, as rated by the Smith Rating Scale. Patients with trunk and extremity movements showed no reduction in their body weight. However, three of four patients who exhibited respiratory TD, with or without oesophageal involvement, were found to have a significant reduction in their body weight after the appearance of TD, as compared to their condition before.
Configuration Selection, Modeling, and Preliminary Testing in Support of Constant Force Electrical Connectors
Authors: Weight Brent L. , Mattson Christopher A. , Magleby Spencer P. , Howell Larry L.
Published: August 2007

The recent introduction and advancements in design of simple, constant-force mechanisms have created the potential for small-scale, low-cost, constant-force electronic connectors (CFECs). CFECs differ from traditional connectors by the separation or disassociation of contact normal force and contact deflection. By removing the traditional constraints imposed by forces and deflections that are dependent on each other, new types of electronic connectors can be explored. These new designs may lead to smaller and more reliable electronic connectors. In this paper, constant-force mechanisms are adapted to satisfy current industry practices for the design of electronic connectors. Different CFEC configurations are explored and one is selected, prototyped, and used as a proof-of-concept connector for a personal digital assistant (PDA) docking station. The modeling, optimization, and verification of the prototype CFEC is presented. Adaptation of constant-force technology to electronic connectors creates new possibilities in electronic connector designs, including allowing an optimal contact force to be utilized to decrease the effects of fretting and wear, lowering required manufacturing tolerances, reducing the system’s sensitivity to variations introduced by the user, and increasing the system’s robustness in applications where movement or vibrations exist.
Jet Impingement Cooling of Chips Equipped With Multiple Cylindrical Pedestal Fins
Authors: Lee D. H. , Chung Y. S. , Ligrani P. M.
Published: August 2007

Fluid flow and heat transfer characteristics on and around a central pedestal and a secondary pedestal, mounted on a flat surface with an impinging jet, are investigated. Surface Nusselt numbers, pressure coefficients (in the form of normalized wall static pressure relative to freestream static pressure), and flow visualization results are given for jet Reynolds numbers of 23,000 and 2300. The dimensionless nozzle-to-surface distance L∕d is 2, and the nondimensional height of the central pedestal H∕D is 0.5. Results are given for different secondary pedestal heights and locations. Spatially averaged Nusselt numbers measured with secondary pedestals employed are 13% to 33% higher than values measured with no secondary pedestal. Local Nusselt numbers and wall pressure coefficients, measured with the secondary pedestal present, are different from values measured with no secondary pedestal, because of flow reattachment and the two counter-rotating recirculation zones located between the two pedestals, and small local regions of flow separation and recirculation located on top of the secondary pedestal. As such, the present multiple pedestal data with impinging jets are useful for a variety of electronics cooling arrangements.
Stochastic Characterization and Models to Predict Performance Uncertainty in Photonic Packages
Authors: Radhakrishnan S. , Subbarayan G. , Nguyen L. , Mazotti W.
Published: August 2007

There is considerable uncertainty in the prediction of performance of a system, due mainly to idealizations in geometry, material behavior, and loading history. Uncertainties in geometry can be predicted and controlled using tighter tolerances. However, the models currently used to describe material behavior are mostly deterministic. To predict the coupling efficiency of a photonic system to a greater degree of confidence, stochastic analysis procedures are necessary. As part of such an analysis, the behavior of materials must be stochastically characterized. In this paper, we present extensive experimental data on thermally and UV-cured epoxies, typically used in photonic packages to enable stochastic analysis. We perform dynamic mechanical analysis over a wide frequency and temperature range to determine the viscoelastic behavior of the epoxies. We next derive an analytical description of the time-dependent behavior of a vertical cavity surface emitting laser (VCSEL) array bonded to a substrate. We further characterize the variation in the displacement of the VCSEL array due to the stochastic, viscoelastic behavior of the bond epoxy. We carry out Monte Carlo simulation to predict the uncertainty in the coupling efficiency of a generic photonic package. We finally relate the size of the VCSEL laser array to its ability to achieve the required coupling efficiency.
Strain Rate Dependent Constitutive Model of Multiaxial Ratchetting of 63Sn–37Pb Solder
Authors: Chen Gang , Chen Xu , Kim Kwang Soo , Abdel-Karim Mohammad , Sakane Masao
Published: August 2007

A series of multiaxial ratcheting tests were conducted on 63Sn–37Pb solder. A unified viscoplastic constitutive model was developed on the basis of the Ohno–Wang kinematic hardening model, and the rate dependence of the material was taken into consideration by introducing a viscous term. The stress-strain hysteresis loop of 63Sn–37Pb under different strain rates can be simulated reasonably well by the model. However, since the axial ratcheting strain rate of 63Sn–37Pb solder is strongly dependent on the applied shear strain rates in axial/torsional ratcheting, the original constitutive model fails to describe the effect of shear strain rate on the ratcheting strain. To improve the rate sensitivity of the model, the material parameter μi was correlated to the strain rate. Comparisons of the experimental and simulated results verify that the modified constitutive model is able to predict the complicated deformation of 63Sn–37Pb. The effects of axial stress, shear strain range, loading history, and strain rate on ratcheting behavior can be reflected fairly well.
On-Wafer Capacitors Under Mechanical Stress
Authors: Karjalainen Päivi H. , Heino Pekka
Published: August 2007

New packaging materials make it possible to produce flexible system in package (SIP) and system on package (SOP) modules. However, in these the integrated circuits are exposed to increased mechanical stresses. The stresses may become even more severe when thinned chips are used. The effect of mechanical stress on the characteristics of on-wafer capacitors was studied. The mechanical stress increased clearly the resonance frequency of poly-insulator-poly capacitors, but caused only minor impedance changes for metal-insulator-metal capacitors. No fatal stress-induced phenomenon was found and the on-wafer capacitors should also operate correctly in SIP and SOP modules. The test chips were processed with two different complementary metal oxide semiconductor processes and the tested on-wafer capacitors had values of 4.8–47pF.
Thermal Induced Stresses in Bridge-Wire Initiator Glass-to-Metal Seals
Authors: Thompson Luke M. , Maughan Michael R. , Rink Karl K. , Blackketter Donald M. , Stephens Robert R.
Published: August 2007

Cracks have been observed in the insulating glass of bridge-wire initiators that may allow moisture to penetrate the assembly, potentially leading to the corrosion and degradation of the bridge wire and the pyrotechnic material. Degradation of the pyrotechnic or the bridge wire may result in initiator failure or diminished performance. The goal of this research is to determine if the manufacturing processes could produce thermal stresses great enough to crack the glass. A parametric plane stress closed-form solution was used to determine the effects of changing material properties and dimensions of the initiator, and to determine potential stresses within the initiator from two different manufacturing scenarios. To verify and expand the plane stress closed-form solution, a two-dimensional axisymmetric finite element analysis was performed. To reproduce the two manufacturing scenarios, lumped models and models that included the effects of cooling the initiator were used. Both models showed that if the manufacturing process involves pouring molten glass into the initiator, the potential for cracking exists. Furthermore, if the surface of the initiator cools faster than the center, cracking is more likely.
Simulations of Process-Induced Warpage During IC Encapsulation Process
Authors: Teng Shiang-Yu , Hwang Sheng-Jye
Published: August 2007

Warpage during integrated circuit encapsulation process is a serious problem. Previous researchers had focused on warpage analysis with thermal-induced shrinkage and the cure-induced shrinkage was neglected. A new approach considering both cure- and thermal-induced shrinkage during encapsulation process was presented to predict the amount of warpage. The cure-induced shrinkage was described by the pressure-volume-temperature-cure (P-V-T-C) equation of epoxy. The thermal-induced shrinkage was described by the coefficients of thermal expansion of the component materials. The thin small outline package (TSOP) DBS-27P and low-profile quad flat package (LQFP) LQFP-64, which were manufactured by Philips Semiconductor located in Taiwan and Siliconware Precision Industries Corporation, respectively, were chosen to be the simulation models. By comparing the amount of predicted warpage with the experimental results, it showed that the approach could better predict the amount of warpage than that considering only thermal-induced shrinkage. It was also found that the sign of cure-induced warpage could be opposite to the thermal-induced warpage. Appropriate design of a package to make cure- and thermal-induced shrinkage to be of opposite sign could minimize the warpage of a package.
Spray Cooling of IGBT Devices
Authors: Mertens Robert G. , Chow Louis , Sundaram Kalpathy B. , Cregger R. Brian , Rini Daniel P. , Turek Louis , Saarloos Benjamin A.
Published: August 2007

The popularity and increased usage of insulated gate bipolar transistors (IGBTs) in power control systems have made the problem of cooling them a subject of considerable interest in recent years. In this investigation, a heat flux of 825W∕cm2 at the die was achieved when air-water spray cooling was used to cool IGBTs at high current levels. The junction temperature of the device was measured accurately through voltage-to-temperature characterization. Results from other cooling technologies and other spray cooling experiments were reviewed. A discussion of electrical power losses in IGBTs, due to switching and conduction, is included in this paper. Experiments were conducted on 19 IGBTs, using data collection and software control of the test set. Three types of cooling were explored in this investigation: single-phase convection with water, spray cooling with air-water and spray cooling with steam-water. The results of these experiments show clear advantages of air-water spray cooling IGBTs over other cooling technologies. The applications of spray cooling IGBTs are discussed in open (fixed) and closed (mobile) systems. Current and heat flux levels achieved during this investigation could not have been done using ordinary cooling methods. The techniques used in this investigation clearly demonstrate the superior cooling performance of air-water spray cooling over traditional cooling methods.
Chip to System Levels Thermal Needs and Alternative Thermal Technologies for High Brightness LEDS
Authors: Arik Mehmet , Setlur Anant , Weaver Stanton , Haitko Deborah , Petroski James
Published: August 2007

Light emitting diodes (LEDs) historically have been used for indicators and produced low amounts of heat. The introduction of high brightness LEDs with white light and monochromatic colors has allowed them to penetrate specialty and general illumination applications. The increased electrical currents used to drive the LEDs have resulted in higher heat fluxes than those for average silicon integrated circuits (i.e., ICs). This has created a need to focus more attention on the thermal management engineering of LED power packages. The output of a typical commercial high brightness, 1mm2, LED has exceeded 100lm at drive levels approaching 3W. This corresponds to a heat flux of up to 300W∕cm2. Novel thermal solutions need to address system architectures, packaging, phosphors for light color conversion, and encapsulants and fillers for optical extraction. In this paper, the effect of thermal management on packaging architectures, phosphors, encapsulants, and system design are discussed. Additionally, discussions of microscopic defects due to packaging problems as well as chip active layer defects are presented through experimental and computational findings.
Numerical Investigation of Thermal Dissipation on Quad Flat Package With Unattached Heat Spreader
Authors: Wang Tong Hong , Lai Yi-Shao
Published: August 2007

Due to cost and process considerations, sometimes a drop-in heat spreader is incorporated in a quad flat package, which is not attached to the die pad. Consequently, due to mismatch of thermal expansions of the components, gapping is inevitable on the unattached interface between drop-in heat spreader and die pad during temperature change. The presence of the gap would potentially decrease the reliability and thermal performance of the package. In this paper, gap distributions on the unattached interface and thermal characteristics of a quad flat package implemented with an unattached drop-in heat spreader are examined through the thermal-mechanical coupling analysis. A numerical procedure is proposed to specify film coefficients as functions of gap openings on separated surfaces. Effects of mesh density and interfacial heat transfer conditions on the numerical solutions are then investigated.
A CFD Application to Optimize T-Shaped Fins: Comparisons to the Constructal Theory’s Results
Authors: Lorenzini Giulio , Moretti Simone
Published: August 2007

The problem of heat removal in energetic processes represents a big challenge especially because of the enhanced requirements of the modern industry. The thermal exchange systems therefore have to guarantee better performances in correspondence to ever more severe dimensional constraints. This paper shows a numerical approach, based on computational fluid dynamics (CFD) software, for the evaluation of the heat exchange performances of finned (straight fins) surfaces made of highly heat conductive material. The same geometric constraints assumed in a reference work were adopted. This research attempts to develop an easy-to-use method to face what was previously solved by the powerful approach of Bejan’s Constructal theory. The results obtained show a good agreement between CFD and the Constructal theory’s results, validating, therefore, the simplified approach proposed and encouraging its application to a broader variety of geometries.
Control of Multiagent Systems Using Linear Cyclic Pursuit With Heterogenous Controller Gains
Authors: Sinha A. , Ghose D.
Published: August 2007

In this paper, behavior of a group of autonomous mobile agents under cyclic pursuit is studied. Cyclic pursuit is a simple distributed control law, in which the agent i pursues agent i+1modn. The equations of motion are linear, with no kinematic constraints on motion. Behaviorally, they are identical but may have different controller gains. We generalize existing results in the literature, which consider only homogenous gains, to the case where controller gains are heterogenous. We show that, by selecting suitable controller gains, collective behavior of agents can be controlled significantly to obtain not only point convergence but also directed motion. In particular, we obtain analytical results that relate the controller gains to the direction of movement of the agents when the system is unstable. Invariance results with respect to the pursuit sequence are also proved. Finally, we also obtain some results that show some aspects of system behavior that is invariant with respect to finite switching of connections. Simulation experiments are given in support of the analytical results.
A Composite Model for Vehicle Formation and Path Selection on a Cellular Structured Map
Authors: Zheng Yongling , Özgüner Ümit
Published: August 2007

A new framework for multiple vehicle system modeling and control is proposed in this paper, emphasizing team behavior in a multilevel, multiresolutional way. This framework integrates issues like team formation and path following, so that tasks can easily be allocated to individual and teams of vehicles. The movement of the leader is modeled as a discrete state system within a cellular map, and the movement of the follower is modeled as a hybrid system, including the leader-follower interface. The advantage of this model framework is that it abstracts the main features of the dynamics of multiple vehicle systems in high dimensional spaces into one-dimensional cellular space, and simplifies and extends the model of followers. As an illustration of issues that need to be addressed carefully in the proposed framework, the concept of sharp turns or switch backs, is defined and a switch-back avoidance algorithm presented.