bluuebunny/crossref_metadata_2025 huggingface dataset:
Contact reduction
Authors: Willett Christopher
Published: September 2002

In this article I propose a new method for reducing co-oriented contact manifold

M
M

equipped with an action of a Lie group

G
G

by contact transformations. With a certain regularity and integrality assumption the contact quotient

M
μ

M_\mu

at

μ
∈

g

∗

\mu \in \mathfrak {g}^*

is a naturally co-oriented contact orbifold which is independent of the contact form used to represent the given contact structure. Removing the regularity and integrality assumptions and replacing them with one concerning the existence of a slice, which is satisfied for compact symmetry groups, results in a contact stratified space; i.e., a stratified space equipped with a line bundle which, when restricted to each stratum, defines a co-oriented contact structure. This extends the previous work of the author and E. Lerman.
3-connected planar spaces uniquely embed in the sphere
Authors: Richter R. , Thomassen Carsten
Published: September 2002

We characterize those locally connected subsets of the sphere that have a unique embedding in the sphere — i.e., those for which every homeomorphism of the subset to itself extends to a homeomorphism of the sphere. This implies that if

G
¯

\bar G

is the closure of an embedding of a 3-connected graph in the sphere such that every 1-way infinite path in

G
G

has a unique accumulation point in

G
¯

\bar G

, then

G
¯

\bar G

has a unique embedding in the sphere. In particular, the standard (or Freudenthal) compactification of a 3-connected planar graph embeds uniquely in the sphere.
Summing inclusion maps between symmetric sequence spaces
Authors: Defant Andreas , Mastyło Mieczyslaw , Michels Carsten
Published: September 2002

In 1973/74 Bennett and (independently) Carl proved that for

1
≤
u
≤
2

1 \le u \le 2

the identity map id:

ℓ
u

↪

ℓ
2

\ell _u \hookrightarrow \ell _2

is absolutely

(
u
,
1
)

(u,1)

-summing, i. e., for every unconditionally summable sequence

(

x
n

)

(x_n)

in

ℓ
u

\ell _u

the scalar sequence

(
‖

x
n

‖

ℓ
2

)

(\|x_n \|_{\ell _2})

is contained in

ℓ
u

\ell _u

, which improved upon well-known results of Littlewood and Orlicz. The following substantial extension is our main result: For a

2
2

-concave symmetric Banach sequence space

E
E

the identity map

id
:
E
↪

ℓ
2

\text {id}: E \hookrightarrow \ell _2

is absolutely

(
E
,
1
)

(E,1)

-summing, i. e., for every unconditionally summable sequence

(

x
n

)

(x_n)

in

E
E

the scalar sequence

(
‖

x
n

‖

ℓ
2

)

(\|x_n \|_{\ell _2})

is contained in

E
E

. Various applications are given, e. g., to the theory of eigenvalue distribution of compact operators, where we show that the sequence of eigenvalues of an operator

T
T

on

ℓ
2

\ell _2

with values in a

2
2

-concave symmetric Banach sequence space

E
E

is a multiplier from

ℓ
2

\ell _2

into

E
E

. Furthermore, we prove an asymptotic formula for the

k
k

-th approximation number of the identity map

id
:

ℓ
2
n

↪

E
n

\text {id}: \ell _2^n \hookrightarrow E_n

, where

E
n

E_n

denotes the linear span of the first

n
n

standard unit vectors in

E
E

, and apply it to Lorentz and Orlicz sequence spaces.
𝑎𝑑-nilpotent 𝔟-ideals in 𝔰𝔩(𝔫) having a fixed class of nilpotence: combinatorics and enumeration
Authors: Andrews George , Krattenthaler Christian , Orsina Luigi , Papi Paolo
Published: September 2002

We study the combinatorics of

a
d

ad

-nilpotent ideals of a Borel subalgebra of

s
l
(
n
+
1
,

C

)

sl(n+1,\mathbb C)

. We provide an inductive method for calculating the class of nilpotence of these ideals and formulas for the number of ideals having a given class of nilpotence. We study the relationships between these results and the combinatorics of Dyck paths, based upon a remarkable bijection between

a
d

ad

-nilpotent ideals and Dyck paths. Finally, we propose a

(
q
,
t
)

(q,t)

-analogue of the Catalan number

C
n

C_n

. These

(
q
,
t
)

(q,t)

-Catalan numbers count, on the one hand,

a
d

ad

-nilpotent ideals with respect to dimension and class of nilpotence and, on the other hand, admit interpretations in terms of natural statistics on Dyck paths.
Positivity, sums of squares and the multi-dimensional moment problem
Authors: Kuhlmann S. , Marshall M.
Published: September 2002

Let

K
K

be the basic closed semi-algebraic set in

R

n

\mathbb {R}^n

defined by some finite set of polynomials

S
S

and

T
T

, the preordering generated by

S
S

. For

K
K

compact,

f
f

a polynomial in

n
n

variables nonnegative on

K
K

and real

ϵ
>
0

\epsilon >0

, we have that

f
+
ϵ
∈
T

f+\epsilon \in T

[15]. In particular, the

K
K

-Moment Problem has a positive solution. In the present paper, we study the problem when

K
K

is not compact. For

n
=
1

n=1

, we show that the

K
K

-Moment Problem has a positive solution if and only if

S
S

is the natural description of

K
K

(see Section 1). For

n
≥
2

n\ge 2

, we show that the

K
K

-Moment Problem fails if

K
K

contains a cone of dimension 2. On the other hand, we show that if

K
K

is a cylinder with compact base, then the following property holds:
\[
<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" alttext="left-parenthesis double-dagger right-parenthesis for-all f element-of double-struck upper R left-bracket upper X right-bracket comma f greater-than-or-equal-to 0 on upper K right double arrow there-exists q element-of upper T such that for-all real epsilon greater-than 0 comma f plus epsilon q element-of upper T period">

(
‡
)

∀
f
∈

R

[
X
]
,
f
≥
0
 on 
K
⇒
∃
q
∈
T
 such that 
∀
 real 
ϵ
>
0
,
f
+
ϵ
q
∈
T
.

(\ddagger )\quad \quad \forall f\in \mathbb {R}[X], f\ge 0 \text { on } K\Rightarrow \exists q\in T \text { such that }\forall \text { real } \epsilon >0, f+\epsilon q\in T.\quad

\]
This property is strictly weaker than the one given in [15], but in turn it implies a positive solution to the

K
K

-Moment Problem. Using results of [9], we provide many (noncompact) examples in hypersurfaces for which (

‡
\ddagger

) holds. Finally, we provide a list of 8 open problems.
Shifted simplicial complexes are Laplacian integral
Authors: Duval Art , Reiner Victor
Published: September 2002

We show that the combinatorial Laplace operators associated to the boundary maps in a shifted simplicial complex have all integer spectra. We give a simple combinatorial interpretation for the spectra in terms of vertex degree sequences, generalizing a theorem of Merris for graphs. We also conjecture a majorization inequality for the spectra of these Laplace operators in an arbitrary simplicial complex, with equality achieved if and only if the complex is shifted. This generalizes a conjecture of Grone and Merris for graphs.
From deep holes to free planes
Authors: Zong Chuanming
Published: September 2002

During the last decades, by applying techniques from Number Theory, Combinatorics and Measure Theory, remarkable progress has been made in the study of deep holes, free planes and related topics in packings of convex bodies, especially in lattice ball packings. Meanwhile, some fascinating new problems have been proposed. To stimulate further research in related areas, we will review the main results, some key techniques and some fundamental problems about deep holes, free cylinders and free planes in this paper.
A century of complex Tauberian theory
Authors: Korevaar J.
Published: September 2002

Complex-analytic and related boundary properties of transforms give information on the behavior of pre-images. The transforms may be power series, Dirichlet series or Laplace-type integrals; the pre-images are series (of numbers) or functions.

The chief impulse for complex Tauberian theory came from number theory. The first part of the survey emphasizes methods which permit simple derivations of the prime number theorem, associated with the labels Landau-Wiener-Ikehara and Newman. Other important areas in complex Tauberian theory are associated with the names Fatou-Riesz and Ingham. Recent refinements have been motivated by operator theory and include localH1H^1and pseudofunction boundary behavior of transforms. Complex information has also led to better remainder estimates in connection with classical Tauberian theorems. Applications include the distribution of zeros and eigenvalues.
Ranks of elliptic curves
Authors: Rubin Karl , Silverberg Alice
Published: September 2002

This paper gives a general survey of ranks of elliptic curves over the field of rational numbers. The rank is a measure of the size of the set of rational points. The paper includes discussions of the Birch and Swinnerton-Dyer Conjecture, the Parity Conjecture, ranks in families of quadratic twists, and ways to search for elliptic curves of large rank.
Towards the ample cone of \overline{𝑀}_{𝑔,𝑛}
Authors: Gibney Angela , Keel Sean , Morrison Ian
Published: September 2002

In this paper we study the ample cone of the moduli space

M
¯

g
,
n

\overline {M}_{g,n}

of stable

n
n

-pointed curves of genus

g
g

. Our motivating conjecture is that a divisor on

M
¯

g
,
n

\overline {M}_{g,n}

is ample iff it has positive intersection with all

1
1

-dimensional strata (the components of the locus of curves with at least

3
g
+
n
−
2

3g+n-2

nodes). This translates into a simple conjectural description of the cone by linear inequalities, and, as all the

1
1

-strata are rational, includes the conjecture that the Mori cone is polyhedral and generated by rational curves. Our main result is that the conjecture holds iff it holds for

g
=
0

g=0

. More precisely, there is a natural finite map

r
:

M
¯

0
,
2
g
+
n

→

M
¯

g
,
n

r: \overline {M}_{ 0, 2g+n} \rightarrow \overline {M}_{g,n}

whose image is the locus

R
¯

g
,
n

\overline {R}_{g,n}

of curves with all components rational. Any

1
1

-strata either lies in

R
¯

g
,
n

\overline {R}_{g,n}

or is numerically equivalent to a family

E
E

of elliptic tails, and we show that a divisor

D
D

is nef iff

D
⋅
E
≥
0

D \cdot E \geq 0

and

r

∗

(
D
)

r^{*}(D)

is nef. We also give results on contractions (i.e. morphisms with connected fibers to projective varieties) of

M
¯

g
,
n

\overline {M}_{g,n}

for

g
≥
1

g \geq 1

showing that any fibration factors through a tautological one (given by forgetting points) and that the exceptional locus of any birational contraction is contained in the boundary.
Singularities of pairs via jet schemes
Authors: Mustaţǎ Mircea
Published: September 2002

Let

X
X

be a smooth variety and

Y
⊂
X

Y\subset X

a closed subscheme. We use motivic integration on the space of arcs of

X
X

to characterize the fact that

(
X
,
Y
)

(X,Y)

is log canonical or log terminal using the dimension of the jet schemes of

Y
Y

. This gives a formula for the log canonical threshold of

(
X
,
Y
)

(X,Y)

, which we use to prove a result of Demailly and Kollár on the semicontinuity of log canonical thresholds.
Blow up in finite time and dynamics of blow up solutions for the 𝐿²–critical generalized KdV equation
Authors: Martel Yvan , Merle Frank
Published: September 2002

In this paper, we describe the dynamics of blow up solutions for the critical generalized KdV equation such that the initial data is close to the soliton in

L
2

L^2

and has decay in

L
2

L^2

at the right. In particular, we prove that blow up occurs in finite time, and we obtain an upper bound on the blow up rate.
Torification and factorization of birational maps
Authors: Abramovich Dan , Karu Kalle , Matsuki Kenji , Włodarczyk Jarosław
Published: September 2002

Building on work of the fourth author and Morelli’s work, we prove the weak factorization conjecture for birational maps in characteristic zero: a birational map between complete nonsingular varieties over an algebraically closed field

K
K

of characteristic zero is a composite of blowings up and blowings down with nonsingular centers.
Some closed formulas for canonical bases of Fock spaces
Authors: Leclerc Bernard , Miyachi Hyohe
Published: September 2002

We give some closed formulas for certain vectors of the canonical bases of the Fock space representation ofUv(sln)U_v(\mathfrak {sl}_n). As a result, a combinatorial description of certain parabolic Kazhdan-Lusztig polynomials for affine typeAAis obtained.
Cuspidal local systems and graded Hecke algebras, III
Authors: Lusztig G.
Published: September 2002

We prove a strong induction theorem and classify the tempered and square integrable representations of graded Hecke algebras.
Accuracy of Race Coding on American Indian Death Certificates, Montana 1996–1998
Authors: Harwell Todd S. , Hansen Dina , Moore Kelly R. , Jeanotte Duane , Gohdes Dorothy , Helgerson Steven D.
Published: September 2002

Objectives.

The purpose of this study was to describe the consistency of coding of American Indians on Montana death certificates and to identify the characteristics of American Indians in Montana associated with consistent classification on death certificates.

Methods.

The Billings Area Indian Health Service (IHS) patient registration file was linked with Montana Department of Health and Human Services death certificate files for 1996–1998.

Results.

A total of 769 Montana residents who had died in 1996–1998 were matched to the IHS registration file. Of these decedents, 696 (91%) were consistently classified as American Indian on the death certificate. Seventy-two (99%) of the 73 decedents not classified as Indian were classified as white. American Indians living in counties on or near the seven Montana reservations were more likely to be consistently classified than Indians living in other counties (95% vs. 70%); those with less than 12 years of education (93% vs. 88%) were more likely to be consistently classified than those with 12 or more years of education. Decedents whose cause of death was suicide were less likely than those with other causes of death to be consistently classified (72% vs. 95%). In contrast, a higher percentage of those with an alcohol-related cause of death than of those with other causes of death were consistently classified, although this difference was not statistically significant.

Conclusions.

The mortality rates for Montana American Indians are underestimated overall, and are differentially under- and overestimated for selected conditions.
Preface for a Discussion on Atmospheric chemistry of sulphur in relation to aerosols, clouds, and climate
Authors: Thrush B. A.
Published: September 2002

Preface for a Discussion on Atmospheric chemistry of sulphur in relation to aerosols, clouds, and climate. Held at the Royal Society on 3rd and 4th July 1996. Organized and edited by R. A. Cox, C. N. Hewitt, P. S. Liss, J. E. Lovelock, K. R. Shine and B. A Thrush.
A geophysiologist's thoughts on the natural sulphur cycle
Authors: Lovelock James
Published: September 2002

The climate depends on the atmospheric abundance of sulphur aerosols at all levels up to the stratopause. Volcanoes, combustion and biological emissions all contribute and usually result in cooling. The history of this topic is lively and goes back at least to the eighteenth century with Benjamin Franklin's comments on the cooling effects of the sulphuric acid aerosol from the Icelandic volcano, Laki. Mitchell first drew attention to the potential cooling effects of combustion aerosols. Charlson and his colleagues proposed that emissions of dimethyl sulphide (DMS) from ocean algae might also be important. More recently, Lovelock and Kump drew attention to the decline of biological sulphur emissions with global warming and the possible consequence of a positive feedback on climate change. The geophysiological aspects, which arose from the Gaia hypothesis in the early 1970s, form an important part of the account that follows.
Terrestrial sources and distribution of atmospheric sulphur
Authors: Lelieveld J. , Roelofs G.–J. , Ganzeveld L. , Feichter J. , Rodhe H.
Published: September 2002

The general circulation model ECHAM has been coupled to a chemistry and sulphur cycle model to study the impact of terrestrial, i.e. mostly anthropogenic sulphur dioxide (SO2), sources on global distributions of sulphur species in the atmosphere. We briefly address currently available source inventories. It appears that global estimates of natural emissions are associated with uncertainties up to a factor of 2, while anthropogenic emissions have uncertainty ranges of about +/− 30 per cent. Further, some recent improvements in the model descriptions of multiphase chemistry and deposition processes are presented. Dry deposition is modelled consistently with meteorological processes and surface properties. The results indicate that surface removal of SO2is less efficient than previously assumed, and that the SO2lifetime is thus longer. Coupling of the photochemistry and sulphur chemistry schemes in the model improves the treatment of multiphase processes such as oxidant (hydrogen peroxide) supply in aqueous phase SO2oxidation. The results suggest that SO2oxidation by ozone (O3) in the aqueous phase is more important than indicated in earlier work. However, it appears that we still overestimate atmospheric SO2concentrations near the surface in the relatively polluted Northern Hemisphere. On the other hand, we somewhat underestimate sulphate levels in these regions, which suggests that additional heterogeneous reaction mechanisms, e.g. on aerosols, enhance SO2oxidation.
Marine sulphur emissions
Authors: Liss Peter S. , Hatton Angela D. , Malin Gill , Nightingale Philip D. , Turner Suzanne M.
Published: September 2002

The principal volatile sulphur species found in seawater are dimethyl sulphide (DMS), carbonyl sulphide (COS) and carbon disulphide (CS2. Of these, DMS is the most abundant and widespread in its distribution. The predominant oceanic source of DMS is dimethylsulphonioproprionate (DMSP), a compatible solute synthesized by phytoplankton for osmoregulation and/or cryoprotection. Not all species have the same ability to form DMSP; for example, diatoms generally produce little, whereas prymnesiophytes and some dinoflagellates make significantly larger amounts. Much of the release of DMSP and DMS to the water occurs on death or through predation of the plankton. Our recent field data strongly suggest that oxidation of DMS to dimethyl sulphoxide (DMSO) is an important process in the water column, and it is clear that considerable internal cycling in the DMSP/DMS/DMSO system occurs in the euphotic zone. A fraction of the DMS crosses the sea surface and enters the atmosphere where it is oxidized by radicals such OH and NO3to form products such as methanesulphonate (MSA), DMSO and non-sea salt sulphate (NSSS) particles. These particles are the main source of cloud condensation nuclei (CCN) over oceanic areas remote from land.
Oxidation of atmospheric reduced sulphur compounds: perspective from laboratory studies
Authors: Ravishankara A. R. , Rudich Yinon , Talukdar Ranajit , Barone Stephen B.
Published: September 2002

Results of laboratory experiments which address the course of the OH + DMS (dimethyl sulphide) reaction in the atmosphere are presented. It is shown that OH reacts via a complex sequence of reactions to produce CH3S and other products, and argued that NO3is unlikely to be an important oxidizer of DMS in the marine boundary layer (MBL) because it is very efficiently taken up by water droplets. A simplified mechanism for the oxidation of DMS in the troposphere is presented. This mechanism explains some of the field observations on the end products of DMS oxidation and their variations with temperature.
Field measurements of dimethyl sulphide and its oxidation products in the atmosphere
Authors: Hewitt C. Nicholas , Davison Brian
Published: September 2002

Dimethyl sulphide (DMS) is released into ocean waters by phytoplankton and may then cross the water–air interface into the atmosphere. Various models have been formulated to describe its behaviour in the atmosphere. Here, measurements of its concentrations and those of its major oxidation products, methane sulphonate, sulphur dioxide, non sea–salt sulphate and demethyl sulphoxide, in both the gas and aerosol phases, in Atlandtic air, are used to validate these qualitative descriptions of its oxidation. Behaviour consistent with day–time oxidation by the hydroxyl radical, with the yield of methane sulphonic acid being both temperature dependent and under the influence of the nitrogen dioxide mixing ratio, is seen. The rapid production of new particles also seems likely under certain conditions but it is not clear whether or not they enhance the concentrations of cloud condensation nuclei in the maritime troposphere. In maritime air a substantial fraction of the sulphate formed appears to be neutralized by reaction with ammonia to form ammonium aerosol.
Recent progress in understanding particle nucleation and growth
Authors: Eisele F. L. , McMurry P. H.
Published: September 2002

In the past half decade, several new tools have become available for investigating particle nucleation and growth. A number of joint field and laboratory studies exploiting some of these new measurement capabilities will be described and new insights shared. the ability to measure OH, SO2, H2SO4and aerosol number and size distributions has made possible a comparison between H2SO4production and loss onto particles in continental air masses. In regions remote from urban emissions, agreement is typically quite good. In contrast, joint field measurements of nucleation precursors such as gas phase H2SO4and ultrafine particles suggest that classical bimolecular nucleation theory may not properly describe the tropospheric nucleation process. An alternative mechanism, possibly involving ammonia as a stabilizing agent for H2SO4/H2O molecular clusters is discussed. Finally, ultrafine particle measurements are shown to offer new opportunities for studying particle growth rates. Preliminary results suggest that in a remote continental air mass, gas phase H2SO4uptake is far too slow to explain observed growth rates.
Atmospheric sulphur and cloud condensation nuclei in marine air in the Southern Hemisphere
Authors: Ayers G. P. , Cainey J. M. , Gillett R. W. , Ivey J. P.
Published: September 2002

Measurements of atmospheric sulphur species made in Southern Ocean air, at the Cape Grim Baseline Air Pollution Station, are reviewed in an attempt to discern the role played by oceanic emissions of dimethyl sulphide (DMS) as a source of cloud condensation nuclei (CCN). Consistent with conclusions reached by others, our data indicate that the connection between DMS concentration and CCN concentration is neither simple nor direct, being mediated through a range of chemical pathways and intermediate species that are subject to considerable variability over timescales ranging from minutes to months. Physical and meteorological processes are no less important than chemical processes as sources of complexity in the DMS to CCN transformation process. Moreover, the considerable uncertainty that currently exists about both the number of chemical pathways involved in DMS oxidation, and the kinetic coefficients associated with the proposed pathways, make quantitative modelling studies problematic.

Nevertheless, synthesis of a large body of data available from Cape Grim and other Southern Ocean sites does permit some refinement of our understanding of the DMS–CCN connection. Here, these data are employed to illustrate the current state of knowledge about the connections between DMS, CCN and cloud properties at Cape Grim, and to highlight the many complexities that underlie these connections.
The effect of sulphur chemistry on the scattering properties of particles
Authors: Choularton T. W. , Bower K. N. , Gallagher M. W.
Published: September 2002

A model has been developed of the interaction of aerosol with shallow layer clouds. The model includes aqueous phase chemical processes, particularly the oxidation of sulphur dioxide (SO
2
) occurring in droplets formed on cloud condensation nuclei of known chemical composition. The cloud microphysics as a function of height above cloud base is predicted along with changes to the aerosol size distribution and hygroscopic properties after a single cycle through cloud. The predictions of the model are compared with observations from a hill cap cloud experiment for a single cloud pass. A stratocumulus cloud model then examines the changes in the cloud microphysics and aerosol population arising as the modified aerosol distribution undergoes a further passage through cloud. The cycling process is repeated a further nine times. We show that the cloud processing of the aerosol results in a strongly bimodal aerosol size distribution which can significantly affect the direct radiative forcing of the aerosol. The processing is strongly oxidant-limited and forced entrainment of hydrogen peroxide through cloud top is required to maintain the oxidation. A strong surface source of ammonia substantially enhances the observed modification. The processing affects the cloud condensation nucleus spectrum, initially increasing the number of droplets activated. However, multiple cycling has a tendency to stabilize the droplet number.
Climate model studies of sulphate aerosols and clouds
Authors: Jones A. , Slingo A.
Published: September 2002

It is generally believed that increases in the atmospheric concentrations of greenhouse gases as a result of man's activities are leading to global warming. It is also believed that the same activities lead to increasing concentrations of sulphate aerosol, which act to cool the climate system and ameliorate the warming. The sulphate cooling may be separated into the direct effect in cloud–free regions and the indirect effect in cloudy regions. This paper summarizes recent work at the Hadley Centre on the indirect effect. Results from two versions of the hadley Centre Climate Model are shown, using various parameterizations linking the amountof sulphate aerosol and the number concentration of droplets in water clouds. These results illustrate the considerable uncertainties in estimating the indirect effect. It is shown that other naturally occurring components of the aerosol population, in particular sea salt, may be important in reducing the magnitude of the indirect effect.
The missing climate forcing
Authors: Hansen J. , Sato M. , Lacis A. , Ruedy R.
Published: September 2002

Observed climate change is consistent with radiative forcings on several time–scales for which the dominant forcings are known, ranging from the few years after a large volcanic eruption to glacial–to–interglacial changes. In the period with most detailed data, 1979 to the present, climate observations contain clear signatures of both natural and anthropogenic forcings. But in the full period since the industrial revolution began, global warming is only about half of that expected due to the principal forcing, increasing greenhouse gases. The direct radiative effect of anthropogenic aerosols contributes only little towards resolving this discrepancy. Unforced climate variability is an unlikely explanation. We argue on the basis of several lines of indirect evidence that aerosol effects on clouds have caused a large negative forcing, at least −1 Wm−2, which has substantially offset greenhouse warming. The tasks of observing this forcing and determining the microphysical mechanisms at its basis are exceptionally difficult, but they are essential for the prognosis of future climate change.
Ice–core records of atmospheric sulphur
Authors: Legrand Michel
Published: September 2002

Sulphate and methanesulphonate (MSA), the two major sulphur species trapped in polar ice, have been extensivelyh studied in Antarctic and Greenland ice cores spanning the last centuries, as well as the entire last climatic cycle. Data from the cores are used to investigate the past contribution of volcanic and biogenic emissions to the natural sulphur budget in high latitude regions of both Hemispheres. Sulphate concentrations in polar ice very often increased during one or two years after large volcanic eruptions. Sulphate records show that fossil fuel combustion has enhanced sulphate concentrations in Greenland snow by a factor of 4 since the beginning of this century, and that no similar trend has occurred in Antarctica. At present, sulphate in Antarctic snow is mainly marine and biogenic in origin and the rate of dimethyl sulphide (DMS) emissions may have been enhanced during pst developments of El Niño Southern Oscillations (ENSO). Marine biota and non–eruptive volcanic emissions represent the two main contributors to the natural high northern latitude sulphur budget. Whele these two sources have contributed equally to the natural sulphur budget of Greenland ice over the last 9000 years BP, non–eruptive volcanic emissions largely dominated the budget at the beginning of the Holocene. A general negative correlation is observed between surcace air temperatures of the Northern Hemisphere and Greenland snow MSA concentrations over the last two centuries. Positive sea–ice anomalies also seem to strengthen DMS emissions. A steady decrease of MSA is observed in Greenland snow layers deposited since 1945, which may either be related to decreasing DMS emissions from marine biota at high northern latitudes or a changing yield of MSA from DMS oxidation driven by modification of the oxidative capacity of the atmosphere in these regions. Slightly reduced MSA concentrations are obvserved in Greenland glacial ice with respect to interglacial levels. In contrast, sulphate and calcium levels are strongly enhanced during the ice age compared to the present day. These long–term variations in Greenland cores are opposite in sign to those revealed by Antarctic ice cores. Such a difference suggests that climate changes led to a quite different sulphur cycle response in the two Hemispheres.
Atmospheric sulphur and climate—what have we learned?
Authors: Cox R. A.
Published: September 2002

Background to the discussion meeting–Atmospheric chemistry of sulphur in relation to aerosols, clouds, and climate–held on 3–4 July 1996 at The Royal Society, London
High performance learning at work
Authors: Teare Richard , Ingram Hadyn , Prestoungrange Gordon , Sandelands Eric
Published: September 2002

Contends that high performance in terms of managerial learning, attainment and return on investment in learning can be readily achieved using the process of action learning. Profiles the contemporary origins of action learning and its application to business challenges and argues that it is the most appropriate learning approach for corporate business school/university structures. Suggests that to add value to the enterprise itself and to recognize the individual, companies should invest in their own accredited learning rather than sending high potential people away from the organization to study. Provides a case study illustration of how one UK hospitality firm secured a significant return on investment in learning during the early pilot work for IMCA Socrates – a corporate business school solution that offers an embedded system for accrediting learning at work.
Modular Subgroup Arithmetic and a Theorem of Philip Hall
Authors: Müller Thomas W.
Published: September 2002

A surprising relationship is established in this paper, between the behaviour modulo a prime p of the number Sn G of index n subgroups in a group G, and that of the corresponding subgroup numbers for a normal subgroup in G normal subgroup in p‐power order. The proof relies, among other things, on a twisted version due to Philip Hall of Frobenius' theorem concerning the equation xm=1 in finite groups. One of the applications of this result, presented here, concerns the explicit determination modulo p of Sn G in the case when G is the fundamental group of a tree of groups all of whose vertex groups are cyclic of p‐power order. Furthermore, a criterion is established (by a different technique) for the function Sn G to be periodic modulo p. 2000 Mathematics Subject Classification 20E06, 20F99 (primary); 05A15, 05E99 (secondary).
ISOPERIMETRIC INEQUALITIES: DIFFERENTIAL GEOMETRIC AND ANALYTIC PERSPECTIVES (Cambridge Tracts in Mathematics 145)
Authors: Grigor'yan Alexander
Published: September 2002

By Isaac Chavel: 268 pp., £50.00, isbn 0‐521‐80267‐9 (Cambridge University Press, 2001).
Mechanism of ToxT-Dependent Transcriptional Activation at theVibrio cholerae tcpAPromoter
Authors: Hulbert Robin R. , Taylor Ronald K.
Published: September 2002

The AraC homolog ToxT coordinately regulates virulence gene expression inVibrio cholerae. ToxT is required for transcriptional activation of the genes encoding cholera toxin and the toxin coregulated pilus, among others. In this work we focused on the interaction of ToxT with thetcpApromoter and investigated the mechanism of ToxT-dependent transcriptional activation attcpA.Deletion analysis showed that a region from −95 to +2 was sufficient for ToxT binding and activation, both of which were simultaneously lost when the deletion was extended to −63. A collection of point mutations generated by error-prone PCR revealed two small regions required for ToxT-dependent transactivation. Binding studies performed with representative mutations showed that the two regions define sites at which ToxT binds to thetcpApromoter region, most likely as a dimer. Results obtained by using arpoAtruncation mutation showed that ToxT-dependent activation attcpAinvolves the C-terminal domain of the RNA polymerase alpha subunit. A model of ToxT-dependent transcriptional activation attcpAis proposed, in which ToxT interacts with two A-rich regions oftcpAcentered at −72 and −51 and requires the alpha C-terminal domain of RNA polymerase.
Mutation inyaaTLeads to Significant Inhibition of Phosphorelay during Sporulation inBacillus subtilis
Authors: Hosoya Shigeo , Asai Kei , Ogasawara Naotake , Takeuchi Michio , Sato Tsutomu
Published: September 2002

In the course of aBacillus subtilisfunctional genomics project which involved screening for sporulation genes, we identified an open reading frame,yaaT, whose disruptant exhibits a sporulation defect. Twenty-four hours after the initiation of sporulation, most cells of theyaaTmutant exhibited stage 0 of sporulation, indicating that theyaaTmutation blocks sporulation at an early stage. Furthermore, the mutation inyaaTled to a significant decrease in transcription from a promoter controlled by Spo0A, a key response regulator required for the initiation of sporulation. However, neither the level of transcription ofspo0A, the activity of σH, which transcribesspo0A, nor the amount of Spo0A protein was severely affected by the mutation inyaaT. Bypassing the phosphorelay by introducing anspo0Amutation (sof-1) into theyaaTmutant suppressed the sporulation defect, suggesting that theyaaTmutation interferes with the phosphorelay process comprising Spo0F, Spo0B, and histidine kinases. We also observed that mutation ofspo0E, which encodes the phosphatase that dephosphorylates Spo0A-P, suppressed the sporulation defect in theyaaTmutant. These results strongly suggest thatyaaTplays a significant role in the transduction of signals to the phosphorelay for initiation of sporulation. Micrographs indicated that YaaT-green fluorescent protein localizes to the peripheral membrane, as well as to the septum, during sporulation.
DistinctclpPGenes Control Specific Adaptive Responses inBacillus thuringiensis
Authors: Fedhila Sinda , Msadek Tarek , Nel Patricia , Lereclus Didier
Published: September 2002

ClpP and ClpC are subunits of the Clp ATP-dependent protease, which is ubiquitous among prokaryotic and eukaryotic organisms. The role of these proteins in stress tolerance, stationary-phase adaptive responses, and virulence in many bacterial species has been demonstrated. Based on the amino acid sequences of theBacillus subtilis clpCandclpPgenes, we identified oneclpCgene and twoclpPgenes (designatedclpP1andclpP2) inBacillus thuringiensis.Predicted proteins ClpP1 and ClpP2 have approximately 88 and 67% amino acid sequence identity with ClpP ofB. subtilis, respectively. Inactivation ofclpCinB. thuringiensisimpaired sporulation efficiency. TheclpP1andclpP2mutants were both slightly susceptible to salt stress, whereas disruption ofclpP2negatively affected sporulation and abolished motility. Virulence of theclpmutants was assessed by injecting bacteria into the hemocoel ofBombyx morilarvae. TheclpP1mutant displayed attenuated virulence, which appeared to be related to its inability to grow at low temperature (25°C), suggesting an essential role for ClpP1 in tolerance of low temperature. Microscopic examination ofclpP1mutant cells grown at 25°C showed altered bacterial division, with cells remaining attached after septum formation. Analysis oflacZtranscriptional fusions showed thatclpP1was expressed at 25 and 37°C during the entire growth cycle. In contrast,clpP2was expressed at 37°C but not at 25°C, suggesting that ClpP2 cannot compensate for the absence of ClpP1 in theclpP1mutant cells at low temperature. Our study demonstrates that ClpP1 and ClpP2 control distinct cellular regulatory pathways inB. thuringiensis.
Evidence for Targeting of Yop Effectors by the Chromosomally Encoded Ysa Type III Secretion System ofYersinia enterocolitica
Authors: Young Briana M. , Young Glenn M.
Published: September 2002

Yersinia enterocoliticaO:8 has two contact-dependent type III secretion systems (TTSSs). The Ysa TTSS is encoded by a set of genes located on the chromosome and exports Ysp proteins. The Ysc TTSS and the Yop effector proteins it exports are encoded by genes located on plasmid pYVe8081. In this study, secretion of YspG, YspH, and YspJ by the Ysa TTSS was shown to require pYVe8081. Furthermore, mutations that blocked the function of the Ysc TTSS did not affect YspG, YspH, and YspJ production. This indicated that YspG, YspH, and YspJ are encoded by genes located on pYVe8081 and that they may correspond to Yops. A comparison of Ysps with Yop effectors secreted byY. enterocoliticaindicated that YspG, YspH, and YspJ have apparent molecular masses similar to those of YopN, YopP, and YopE, respectively. Immunoblot analysis demonstrated that antibodies directed against YopN, YopP, and YopE recognized YspG, YspH, and YspJ. Furthermore, mutations inyopN,yopP, andyopEspecifically blocked YopN, YopP, and YopE secretion by the Ysc TTSS and YspG, YspH, and YspJ secretion by the Ysa TTSS. These results indicate YspG, YspH, and YspJ are actually YopN, YopP, and YopE. Additional analysis demonstrated that YopP and YspH secretion was restored toyopPmutants by complementation intranswith a wild-type copy of theyopPgene. Examination ofY. enterocolitica-infected J774A.1 macrophages revealed that both the Ysc and Ysa TTSSs contribute to YopP-dependent suppression of tumor necrosis factor alpha production. This indicates that both the Ysa and Ysc TTSSs are capable of targeting YopP and that they influenceY. enterocoliticainteractions with macrophages. Taken together, these results suggest that the Ysa and Ysc TTSSs contributeto Y. enterocoliticavirulence by exporting both unique and common subsets of effectors.
A Novel Cytology-Based, Two-Hybrid Screen for Bacteria Applied to Protein-Protein Interaction Studies of a Type IV Secretion System
Authors: Ding Zhiyong , Zhao Zhenming , Jakubowski Simon J. , Krishnamohan Atmakuri , Margolin William , Christie Peter J.
Published: September 2002

DivIVA ofBacillus subtilisand FtsZ ofEscherichia coliwere used to target heterologous protein complexes to cell division sites ofE. coliandAgrobacterium tumefaciens. DivIVA and FtsZ that were fused to the dimerizing leucine zipper (LZ) domain of the yeast transcription activator GCN4 directed the green fluorescent protein (GFP) that was fused to an LZ domain toE. colidivision sites, resulting in fluorescence patterns identical to those observed with DivIVA::GFP and FtsZ::GFP. These cell division proteins also targeted the VirE1 chaperone and VirE2 secretion substrate complex to division sites ofE. coliandA. tumefaciens. Coproduction of the native VirE1 or VirE2 proteins inhibited the dihybrid interaction in both species, as judged by loss of GFP targeting to division sites. The VirE1 chaperone bound independently to N- and C-terminal regions of VirE2, with a requirement for residues 84 to 147 and 331 to 405 for these interactions, as shown by dihybrid studies with VirE1::GFP and DivIVA fused to N- and C-terminal VirE2 fragments. DivIVA also targeted homo- and heterotypic complexes of VirB8 and VirB10, two bitopic inner membrane subunits of theA. tumefaciensT-DNA transfer system, inE. coliand homotypic complexes of VirB10 inA. tumefaciens.VirB10 self-association in bacteria was mediated by the C-terminal periplasmic domain, as shown by dihybrid studies with fusions to VirB10 truncation derivatives. Together, our findings establish a proof-of-concept for the use of cell-location-specific proteins for studies of interactions among cytosolic and membrane proteins in diverse bacterial species.
Protein-Protein Interactions That Regulate the Energy Stress Activation of σBinBacillus subtilis
Authors: Delumeau Olivier , Lewis Richard J. , Yudkin Michael D.
Published: September 2002

σBis an alternative σ factor that controls the general stress response inBacillus subtilis. In the absence of stress, σBis negatively regulated by anti-σ factor RsbW. RsbW is also a protein kinase which can phosphorylate RsbV. When cells are stressed, RsbW binds to unphosphorylated RsbV, produced from the phosphorylated form of RsbV by two phosphatases (RsbU and RsbP) which are activated by stress. We now report the values of theKmfor ATP and theKifor ADP of RsbW (0.9 and 0.19 mM, respectively), which reinforce the idea that the kinase activity of RsbW is directly regulated in vivo by the ratio of these nucleotides. RsbW, purified as a dimer, forms complexes with RsbV and σBwith different stoichiometries, i.e., RsbW2-RsbV2and RsbW2-σB1. As determined by surface plasmon resonance, the dissociation constants of the RsbW-RsbV and RsbW-σBinteractions were found to be similar (63 and 92 nM, respectively). Nonetheless, an analysis of the complexes by nondenaturing polyacrylamide gel electrophoresis in competition assays suggested that the affinity of RsbW2for RsbV is much higher than that for σB. The intracellular concentrations of RsbV, RsbW (as a monomer), and σBmeasured before stress were similar (1.5, 2.6, and 0.9 μM, respectively). After ethanol stress they all increased. The increase was greatest for RsbV, whose concentration reached 13 μM, while those of RsbW (as a monomer) and σBreached 11.8 and 4.9 μM, respectively. We conclude that the higher affinity of RsbW for RsbV than for σB, rather than a difference in the concentrations of RsbV and σB, is the driving force that is responsible for the switch of RsbW to unphosphorylated RsbV.
Tactic Responses to Oxygen in the Phototrophic Bacterium
Rhodobacter sphaeroides
WS8N
Authors: Romagnoli Simona , Packer Helen L. , Armitage Judith P.
Published: September 2002

The temporal and spatial behavior of a number of mutants of the photosynthetic, facultative anaerobe
Rhodobacter sphaeroides
to both step changes and to gradients of oxygen was analyzed. Wild-type cells, grown under a range of conditions, showed microaerophilic behavior, accumulating in a 1.3-mm band about 1.3 mm from the meniscus of capillaries. Evidence suggests this is the result of two signaling pathways. The strength of any response depended on the growth and incubation conditions. Deletion of either the complete chemosensory operons 1 and 2 plus the response regulator genes

cheY
4

and

cheY
5

or

cheA
2

alone led to the loss of all aerotactic responses, although the cells still swam normally. The Prr system of
R. sphaeroides
responds to electron flow through the alternative high-affinity cytochrome oxidase,
cbb
3
, controlling expression of a wide range of metabolic pathways. Mutants with deletions of either the complete Prr operon or the histidine kinase, PrrB, accumulated up to the meniscus but still formed a thick band 1.3 mm from the aerobic interface. This indicates that the negative aerotactic response to high oxygen levels depends on PrrB, but the mutant cells still retain the positive response. Tethered PrrB
−
cells also showed no response to a step-down in oxygen concentration, although those with deletions of the whole operon showed some response. In gradients of oxygen where the concentration was reduced at 0.4 μM/s, tethered wild-type cells showed two different phases of response, with an increase in stopping frequency when the oxygen concentration fell from 80 to 50% dissolved oxygen and a decrease in stopping at 50 to 20% dissolved oxygen, with cells returning to their normal stopping frequency in 0% oxygen. PrrB and CheA
2
mutants showed no response, while PrrCBA mutants still showed some response.
Induction of a DNA Nickase in the Presence of Its Target Site Stimulates Adaptive Mutation in
Escherichia coli
Authors: Rodriguez Cesar , Tompkin Joshua , Hazel Jill , Foster Patricia L.
Published: September 2002

Adaptive mutation to Lac
+
in
Escherichia coli
strain FC40 depends on recombination functions and is enhanced by the expression of conjugal functions. To test the hypothesis that the conjugal function that is important for adaptive mutation is the production of a single-strand nick at the conjugal origin, we supplied an exogenous nicking enzyme, the gene II protein (gIIp) of bacteriophage f1, and placed its target sequence near the
lac
allele. When both gIIp and its target site were present, adaptive mutation was stimulated three- to fourfold. Like normal adaptive mutations, gIIp-induced mutations were

recA
+

and

ruvC
+

dependent and were mainly single-base deletions in runs of iterated bases. In addition, gIIp with its target site could substitute for conjugal functions in adaptive mutation. These results support the hypothesis that nicking at the conjugal origin initiates the recombination that produces adaptive mutations in this strain of
E. coli
, and they suggest that nicking may be the only conjugal function required for adaptive mutation.
Characterization of the Depletion of 2-
C
-Methyl-
d
-Erythritol-2,4-Cyclodiphosphate Synthase in
Escherichia coli
and
Bacillus subtilis
Authors: Campbell Tracey L. , Brown Eric D.
Published: September 2002

The
ispF
gene product in
Escherichia coli
has been shown to catalyze the formation of 2-
C
-methyl-
d
-erythritol 2,4-cyclodiphosphate (MEC) in the deoxyxylulose (DOXP) pathway for isoprenoid biosynthesis. In this work, the
E. coli
gene
ispF
and its
Bacillus subtilis
orthologue,
yacN
, were deleted and conditionally complemented by expression of these genes from distant loci in the respective organisms. In
E. coli
, complementation was achieved through integration of
ispF
at the
araBAD
locus with control from the arabinose-inducible
araBAD
promoter, while in
B. subtilis
,
yacN
was placed at
amyE
under control of the xylose-inducible
xylA
promoter. In both cases, growth was severely retarded in the absence of inducer, consistent with these genes being essential for survival.
E. coli
cells depleted of MEC synthase revealed a filamentous phenotype. This was in contrast to the depletion of MEC synthase in
B. subtilis
, which resulted in a loss of rod shape, irregular septation, multicompartmentalized cells, and thickened cell walls. To probe the nature of the predominant deficiency of MEC synthase-depleted cells, we investigated the sensitivity of these conditionally complemented mutants, grown with various concentrations of inducer, to a wide variety antibiotics. Synthetic lethal behavior in MEC synthase-depleted cells was prevalent for cell wall-active antibiotics.