2,063 research outputs found
Augustus Hamilton’s fossil collection at the Museum of New Zealand Te Papa Tongarewa
Augustus Hamilton (1853–1913) was a New Zealand ethnologist and naturalist who amassed a significant collection of fossils, mostly of birds, during his career. Today, those fossils are housed in the Museum of New Zealand Te Papa Tongarewa (NMNZ). While
some fossils have been catalogued and integrated into the collection of the NMNZ, a large part remained unsorted and uncatalogued.
The present study brings an integrated view of Hamilton’s collection at the NMNZ, highlighting the most significant fossils. In total,
there are 3692 specimen lots collected by Hamilton in the NMNZ representing a large sample of taxa and a wide range of locations
around Aotearoa New Zealand. Most fossils are of Holocene age and belong to birds. The collection includes type specimens, circa
250 specimen lots belonging to extinct species, and specimens belonging to otherwise poorly represented species in natural history
collections. We hope that our study makes Hamilton’s fossils visible and more readily available for future research
A matched expansion approach to practical self-force calculations
We discuss a practical method to compute the self-force on a particle moving
through a curved spacetime. This method involves two expansions to calculate
the self-force, one arising from the particle's immediate past and the other
from the more distant past. The expansion in the immediate past is a covariant
Taylor series and can be carried out for all geometries. The more distant
expansion is a mode sum, and may be carried out in those cases where the wave
equation for the field mediating the self-force admits a mode expansion of the
solution. In particular, this method can be used to calculate the gravitational
self-force for a particle of mass mu orbiting a black hole of mass M to order
mu^2, provided mu/M << 1. We discuss how to use these two expansions to
construct a full self-force, and in particular investigate criteria for
matching the two expansions. As with all methods of computing self-forces for
particles moving in black hole spacetimes, one encounters considerable
technical difficulty in applying this method; nevertheless, it appears that the
convergence of each series is good enough that a practical implementation may
be plausible.Comment: IOP style, 8 eps figures, accepted for publication in a special issue
of Classical and Quantum Gravit
X-Ray and UV Orbital Phase Dependence in LMC X-3
The black-hole binary LMC X-3 is known to be variable on time scales of days
to years. We investigate X-ray and ultraviolet variability in the system as a
function of the 1.7 day binary phase using a 6.4 day observation with the Rossi
X-ray Timing Explorer (RXTE) from December 1998. An abrupt 14% flux decrease,
lasting nearly an entire orbit, is followed by a return to previous flux
levels. This behavior occurs twice, at nearly the same binary phase, but it is
not present in consecutive orbits. When the X-ray flux is at lower intensity, a
periodic amplitude modulation of 7% is evident in data folded modulo the
orbital period. The higher intensity data show weaker correlation with phase.
This is the first report of X-ray variability at the orbital period of LMC X-3.
Archival RXTE observations of LMC X--3 during a high flux state in December
1996 show similar phase dependence. An ultraviolet light curve obtained with
the High Speed Photometer aboard the Hubble Space Telescope shows orbital
modulation consistent with that in the optical, caused by the ellipsoidal
variation of the spatially deformed companion.
The X-ray spectrum of LMC X-3 can be acceptably represented by a
phenomenological disk-black-body plus a power law. Changes in the spectrum of
LMC X-3 during our observations are compatible with earlier observations during
which variations in the 2-10 keV flux are tracked closely by the disk geometry
spectral model parameter.Comment: 11 pages, 7 figures, ApJ in pres
Plasmodium falciparum hydroxymethylbilane synthase does not house any cosynthase activity within the haem biosynthetic pathway
Uroporphyrinogen III, the universal progenitor of macrocyclic, modified tetrapyrroles, is produced from aminolaevulinic acid (ALA) by a conserved pathway involving three enzymes: porphobilinogen synthase (PBGS), hydroxymethylbilane synthase (HmbS) and uroporphyrinogen III synthase (UroS). The gene encoding uroporphyrinogen III synthase has not yet been identified in Plasmodium falciparum, but it has been suggested that this activity is housed inside a bifunctional hybroxymethylbilane synthase (HmbS). Additionally, an unknown protein encoded by PF3D7_1247600 has also been predicted to possess UroS activity. In this study it is demonstrated that neither of these proteins possess UroS activity and the real UroS remains to be identified. This was demonstrated by the failure of codon-optimized genes to complement a defined Escherichia coli hemD− mutant (SASZ31) deficient in UroS activity. Furthermore, HPLC analysis of the oxidized reaction product from recombinant, purified P. falciparum HmbS showed that only uroporphyrin I could be detected (corresponding to hydroxymethylbilane production). No uroporphyrin III was detected, showing that P. falciparum HmbS does not have UroS activity and can only catalyze the formation of hydroxymethylbilane from porphobilinogen
Mathematical coupling causes spurious correlation within the conventional acute-to-chronic workload ratio calculations.
The acute-to-chronic workload ratio:An inaccurate scaling index for an unnecessary normalisation process?
Effect of Vehicle on the Nasal Absorption of Epinephrine During Cardiopulmonary Resuscitation
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/90174/1/j.1875-9114.1996.tb03030.x.pd
FAD binding, cobinamide binding and active site communication in the corrin reductase (CobR)
Adenosylcobalamin, the coenzyme form of vitamin B12, is one Nature's most complex coenzyme whose de novo biogenesis proceeds along either an anaerobic or aerobic metabolic pathway. The aerobic synthesis involves reduction of the centrally chelated cobalt metal ion of the corrin ring from Co(II) to Co(I) before adenosylation can take place. A corrin reductase (CobR) enzyme has been identified as the likely agent to catalyse this reduction of the metal ion. Herein, we reveal how Brucella melitensis CobR binds its coenzyme FAD (flavin dinucleotide) and we also show that the enzyme can bind a corrin substrate consistent with its role in reduction of the cobalt of the corrin ring. Stopped-flow kinetics and EPR reveal a mechanistic asymmetry in CobR dimer that provides a potential link between the two electron reduction by NADH to the single electron reduction of Co(II) to Co(I)
DoubleMod and SingleMod: Simple Randomized Secret-Key Encryption with Bounded Homomorphicity
An encryption relation f Z Z with decryption function f 1 is “group-homomorphic”
if, for any suitable plaintexts x1 and x2, x1+x2 = f 1( f (x1)+f (x2)). It is “ring-homomorphic”
if furthermore x1x2 = f 1( f (x1) f (x2)); it is “field-homomorphic” if furthermore 1=x1 =
f 1( f (1=x1)). Such relations would support oblivious processing of encrypted data.
We propose a simple randomized encryption relation f over the integers, called
DoubleMod, which is “bounded ring-homomorphic” or what some call ”somewhat homomorphic.”
Here, “bounded” means that the number of additions and multiplications that can
be performed, while not allowing the encrypted values to go out of range, is limited (any
pre-specified bound on the operation-count can be accommodated). Let R be any large integer.
For any plaintext x 2 ZR, DoubleMod encrypts x as f (x) = x + au + bv, where a
and b are randomly chosen integers in some appropriate interval, while (u; v) is the secret
key. Here u > R2 is a large prime and the smallest prime factor of v exceeds u. With
knowledge of the key, but not of a and b, the receiver decrypts the ciphertext by computing
f 1(y) = (y mod v) mod u.
DoubleMod generalizes an independent idea of van Dijk et al. 2010. We present and
refine a new CCA1 chosen-ciphertext attack that finds the secret key of both systems (ours
and van Dijk et al.’s) in linear time in the bit length of the security parameter. Under a
known-plaintext attack, breaking DoubleMod is at most as hard as solving the Approximate
GCD (AGCD) problem. The complexity of AGCD is not known.
We also introduce the SingleMod field-homomorphic cryptosystems. The simplest
SingleMod system based on the integers can be broken trivially. We had hoped, that if
SingleMod is implemented inside non-Euclidean quadratic or higher-order fields with large
discriminants, where GCD computations appear di cult, it may be feasible to achieve a
desired level of security. We show, however, that a variation of our chosen-ciphertext attack
works against SingleMod even in non-Euclidean fields
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