1,395 research outputs found
Chlamydia protein Pgp3 studied at high resolution in a new crystal form
The protein Pgp3 is implicated in the sexually transmitted disease chlamydia and comprises an extended complex arrangement of a C terminal domain (CTD) and an N terminal domain (NTD), each linked by a triple helix coiled coil (THCC). We report the X-ray crystal structure of Pgp3 from a LGV1 strain at the highest X-ray diffraction resolution obtained to date for the full protein. The protein was crystallised using a high KBr salt concentration, which resulted in a new crystal form with relatively low solvent content diffracting to a resolution of 1.98 Ă
. We describe the 3D structure of this new crystal form, compare it with other crystal forms, describe the KBr salt binding sites and the relevance to chlamydia isolates from around the globe. The crystal packing is apparently driven by the CTDs. Since the three fold axes of the THCC and NTD are not collinear with a CTDâs three fold axis this naturally leads to a disorder in the THCC and the portion of the NTD not directly interacting with the CTD via crystal packing. The key avenue to resolve these oddities of the crystal structure analysis was a complete new analysis in space group P1 and determining the space group as P212121. This space group assignment was the one originally determined from the diffraction pattern but perhaps complicated by a translational non crystallographic symmetry. We found this crystal structure of a three domain multi macromolecular complex, with two misaligned three fold axes, a unique challenge, something not encountered before. A specific intermolecular interaction, possibly of functional significance in receptor binding in chlamydia, we suggest might allow design of a new chemotherapeutic agent against chlamydia
Particle Creation If a Cosmic String Snaps
We calculate the Bogolubov coefficients for a metric which describes the
snapping of a cosmic string. If we insist on a matching condition for all times
{\it and} a particle interpretation, we find no particle creation.Comment: 10 pages, MRC.PH.17/9
'Choosing shoes': a preliminary study into the challenges facing clinicians in assessing footwear for rheumatoid patients
Background: Footwear has been accepted as a therapeutic intervention for the foot affected
by rheumatoid arthritis (RA). Evidence relating to the objective assessment of footwear in
patients with RA is limited. The aims of this study were to identify current footwear styles,
footwear characteristics, and factors that influence footwear choice experienced by patients
with RA.
Methods: Eighty patients with RA were recruited from rheumatology clinics during the
summer months. Clinical characteristics, global function, and foot impairment and disability
measures were recorded. Current footwear, footwear characteristics and the factors
associated with choice of footwear were identified. Suitability of footwear was recorded using
pre-determined criteria for assessing footwear type, based on a previous study of foot pain.
Results: The patients had longstanding RA with moderate-to severe disability and
impairment. The foot and ankle assessment demonstrated a low-arch profile with both
forefoot and rearfoot structural deformities. Over 50% of shoes worn by patients were opentype
footwear. More than 70% of patientsâ footwear was defined as being poor. Poor
footwear characteristics such as heel rigidity and sole hardness were observed. Patients
reported comfort (17%) and fit (14%) as important factors in choosing their own footwear.
Only five percent (5%) of patients wore therapeutic footwear.
Conclusions: The majority of patients with RA wear footwear that has been previously
described as poor. Future work needs to aim to define and justify the specific features of
footwear that may be of benefit to foot health for people with RA
The World-Trade Web: Topological Properties, Dynamics, and Evolution
This paper studies the statistical properties of the web of import-export
relationships among world countries using a weighted-network approach. We
analyze how the distributions of the most important network statistics
measuring connectivity, assortativity, clustering and centrality have
co-evolved over time. We show that all node-statistic distributions and their
correlation structure have remained surprisingly stable in the last 20 years --
and are likely to do so in the future. Conversely, the distribution of
(positive) link weights is slowly moving from a log-normal density towards a
power law. We also characterize the autoregressive properties of
network-statistics dynamics. We find that network-statistics growth rates are
well-proxied by fat-tailed densities like the Laplace or the asymmetric
exponential-power. Finally, we find that all our results are reasonably robust
to a few alternative, economically-meaningful, weighting schemes.Comment: 44 pages, 39 eps figure
Colliding Hadrons as Cosmic Membranes and Possible Signatures of Lost Momentum
We argue that in the TeV-gravity scenario high energy hadrons colliding on
the 3-brane embedded in D=4+n-dimensional spacetime, with n dimensions smaller
than the hadron size, can be considered as cosmic membranes. In the
5-dimensional case these cosmic membranes produce effects similar to cosmic
strings in the 4-dimensional world. We calculate the corrections to the eikonal
approximation for the gravitational scattering of partons due to the presence
of effective hadron cosmic membranes. Cosmic membranes dominate the momentum
lost in the longitudinal direction for colliding particles that opens new
channels for particle decays.Comment: 15 pages, Late
Ground State Energy of Massive Scalar Field Inside a Spherical Region in the Global Monopole Background
Using the zeta function regularization method we calculate the ground state
energy of scalar massive field inside a spherical region in the space-time of a
point-like global monopole. Two cases are investigated: (i) We calculate the
Casimir energy inside a sphere of radius and make an analytical analysis
about it. We observe that this energy may be positive or negative depending on
metric coefficient and non-conformal coupling . In the limit
we found a zero result. (ii) In the second model we surround the
monopole by additional sphere of radius and consider scalar field
confined in the region between these two spheres. In the latter, the ground
state energy presents an additional contribution due to boundary at which
is divergent for small radius. Additional comments about renormalization are
considered.Comment: 30 pages and 2 figures. LATEX fil
Energy Production in the Formation of a Finite Thickness Cosmic String
The classical electromagnetic modes outside a long, straight, superconducting
cosmic string are calculated, assuming the string to be surrounded by a
superconducting cylindric surface of radius R. Thereafter, by use of a
Bogoliubov-type argument, the electromagnetic energy W produced per unit length
in the lowest two modes is calculated when the string is formed "suddenly". The
essential new element in the present analysis as compared with prior work of
Parker [Phys. Rev. Lett. {\bf 59}, 1369 (1987)] and Brevik and Toverud [Phys.
Rev. D {\bf 51}, 691 (1995)], is that the radius {\it a} of the string is
assumed finite, thus necessitating Neumann functions to be included in the
fundamental modes. We find that the theory is changed significantly: W is now
strongly concentrated in the lowest mode , whereas the
proportionality that is characteristic for zero-width
strings is found in the next mode (1,1). Here G is the gravitational constant,
the string mass per unit length, and t the GUT time.Comment: 20 pages, LaTeX, no figure
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