3,046 research outputs found
Branes with Background Fields in Boundary State Formalism
Interaction of branes in presence of internal gauge fields is considered by
using the boundary state formalism. This approach enables us to consider the
problems that are not easily accessible to the canonical approach via open
strings. The effects of compactification of some of the dimensions on tori are
also discussed. Also we study the massless state contribution on this
interaction.Comment: 12 pp. No figure
Mixed Boundary Conditions and Brane-String Bound States
In this article we consider open strings with mixed boundary conditions (a
combination of Neumann and Dirichlet conditions at each end). We discuss how
their end points show a -brane with NS-NS charge, i.e. a bound state of a
D-brane with a fundamental strings. We show that these branes are BPS
saturated. In the case of one-branes, we show that their mass densities are in
agreement with IIb SUGRA which is Sl(2,Z) invariant. Using Chan-Paton factors,
we extend our results to the case of bound states of D-strings and
F-strings. These string theoretic results are also checked in the effective
field theory limit.Comment: Latex file, 20 pages, No Figures, some paragraphs adde
p-brane Solitons in Maximal Supergravities
In this paper, we give a construction of -brane solitons in all maximal
supergravity theories in dimensions that are obtainable from
supergravity by dimensional reduction. We first obtain the full bosonic
Lagrangians for all these theories in a formalism adapted to the -brane
soliton construction. The solutions that we consider involve one dilaton field
and one antisymmetric tensor field strength, which are in general linear
combinations of the basic fields of the supergravity theories. We also study
the supersymmetry properties of the solutions by calculating the eigenvalues of
the Bogomol'nyi matrices, which are derived from the commutators of the
supercharges. We give an exhaustive list of the supersymmetric -brane
solutions using field strengths of all degrees , and the
non-supersymmetric solutions for . As well as studying elementary and
solitonic solutions, we also discuss dyonic solutions in and . In
particular, we find that the Bogomol'nyi matrices for the supersymmetric
massless dyonic solutions have indefinite signature.Comment: 31 pages, Latex, no figure
Mixed Branes Interaction in Compact Spacetime
We present a general description of two mixed branes interactions. For this
we consider two mixed branes with dimensions p_1 and p_2, in external field
B_{\mu\nu} and arbitrary gauge fields A^1_{\alpha_1} and A^2_{\alpha_2} on the
world volume of them, in spacetime in which some of its directions are
compactified on circles with different radii. Some examples are considered to
clear these general interactions. Finally contribution of the massless states
on the interactions is extracted. Closed string with mixed boundary conditions
and boundary state formalism, provide useful tools for calculation of these
interactions.Comment: 22 pages, to appear in Nucl. Phys.
Low-Energy Theorems for Gluodynamics at Finite Temperature
We generalize the low-energy theorems of gluodynamics to finite temperature.
Examples of the theorems in the low and high temperature limits are given.Comment: 8 pages latex plus 1 postscript figur
Studies in nuclear cytology
My work falls broadly into three groups of
subjects:1. Studies on the determination of secondary sex
characters in invertebrates : papers 2, 3 and 4.These papers describe research on one of the first
problems which engaged my attention : the causal determination of the differentiation of secondary sex
characters in invertebrates. While I was a student at
Naples in 1938/9 I was impressed by the problem of
parasitic castration and sex reversal in crustacea.
The problem has great physiological and genetic interest
it has also great complexity. This became apparent to me
when I found that the effects of epicarid isopods on their
prawn hosts is quite unlike the action of similar isopods
on Upogebia, this latter animal showing all the familiar
features of sex reversal when parasitised. The castration
of unparasitised prawns by means of X -rays gave evidence
that the cyclically developed female secondary sex
characters are dependent on the presence of a maturing
ovary for their differentiation : the same situation was
found, thong of published, for the adult female
characters of the crab Pachygrapsus, though this animal
undergoes sex reversal, male to female, on being
parasitised. It was hoped that castration of males might
be accomplished by means of X -rays since this would
supply crucial evidence for the resolution of the whole
problem. However, too high a level of irradiation. is
necessary for castration of male crabs, which die before
completing a further moult. Surgical castration likewise
proved impracticable and the problem was left in this
state.2. Studies in chromosome cytology : papers 5,6,70,9,10,
11,14,(16,17),19,20 and 21.My interest in chromosome cytology, originally
aroused by Dr J.R.Baker and Dr E.B.Ford,F.R.S., at Oxford
2.
and further stimulated by contact with Dr C.D.Darlington,
P.R.S., then of Merton,London, led me to study a number
of problems in this field. It is with these problems that
the main bulk of my papers are concerned.Paper 6 demonstrated that a mmltiple chromosome
mechanism determines sex in the earwig. The situation
is complicated by the fact that males may have two
alternative chromosome constitutions and that the Y
chromosome in this species is dicentric :the mechanism
is considered to be related to the abnormal sex ratios in
earwigs which are found in the wild.Paper 8 describes the behaviour of a supernumerary
autosome at meiosis in the grasshopper Mecostethus.
Paper 9 describes how a fertile plant hybrid has
arisen by the hybridisation of two autopolyploid species : this mechanism is an alternative means of arriving at an
alloployploid constitution.Paper 10 describes the discovery of low temperature
sensitive heterochromatic segments of the chromosomes of
newts both at mitosis and meiosis and leads to the inference that desoxyribose nucleic acid ix plays an important
role in chromosome spiralisation.Paper 11 describes _the upsets to the spindle
mechanism at mitosis which can arise as a result of
exposure of newt cells to low temperature or to the action
of colchicine.Paper 14 demonstrates that the centromere is not
necessarily a barrier to chiasma interferenee at meiosis,
as was previously held to be the case. This was first
shown for the mosquito Culex and has subsequently proved
true for many other animal.Paper 19 shows how chiasma interference across the
centromere is suppressed waen multivalent chromosome
associations are formed at meiosis.Papers 20 and 21 describe the reduction in chiasma
frequency and the localisation of chiasmata in hybrids
between geographical races of newts. Evidence is also
given of the origin of a chromosomal translocation which
distinguishes the chromosome complement of one race
from the other two and which can act as a barrier to
genetic leakage between these races.Papers 16 and 17, which do not rightly fall under
the heading of chromosome cytology, are nevertheless_
related to this theme since they are concerned with the
possibility of .a connection between heterorshromatic
chromosome segments, ribose nucleic acid synthesis and
growth rate determination.3. Experimental work with giant nuclei : papers (12, 13),
15, 18, 22, 23.Partly as a result of a controversy over the
distribution of nucleic acid in the cell (papers 12 and
13) and more generally because, having worked for some
years in the field of descriptive cytology and cytogenetics, 1 was impressed with the need for an experimental
attack on the many outstanding and general problems
concerning the cell nucleus, i turned my attention three
years ago to the exploitation of giant nuclei.A great deal of this work is not yet ready for
publication : it is the general line of research in
which I an most actively engaged at the present time.
Since, however, a number of observations have already
been made, these are summarised in a final manuscript
entitled " Experimental studies on amphibian oocyte
nuclei ". This should be read as an introduction to my
published papers in this field.LIST OF PUBLICATIONS:1. 1938. "GUI size in millipedes ". NATURE, 141, 247 ||
2. 1939. "The absence of a sex -hormone controlling
regeneration of the hectocotylus in Octopus
vulgaris Lam. ". Pubbl.Staz.zool.Napoli, 18, 15 ||
3. 1940. "The effects of castration by parasites and .K-rayti
on the secohdary sex chcracters of prawns ".
J. exp. Biol., 17, 168.
|| 4. 1940. (with F.G.i.Knowles) "A change in the chromatophore pattern of crustacea at sexual maturity ".
J. exp. Biol., 17, 262.
|| 5. 1940. "The chromosomes of the cymothoid isopod Anilocra"
Ăuart.J.micr.Sci., 82, 327.
|| 6. 1941. "The sexTdetermining mechanism of the earwig,
Forficula.auricularia ". J.Genet. 41, 349.
|| 7. 1941. "Determination of sex in Scalpellum ".
-NATURE, 148, 258 .
|| 8. 1941. "A trisomic grasshopper ". J.Hered. 32, 296.
|| 9. 1941. "The cytology of Gaulthettya wisleyensis (Marchant
Rehder: a new mode of species formation."
An.n.Bot.Lond.,N.S.5, 579
|| 10. 1942. "Heterochromatin in Triton ". Proc.roy.Soc.
B. 130, 324.
|| 11. 1943. (with H.N.Barber) "The effects of cold and
colchicine on mitosis in the newt ". Proc. roy.
Soc. B. 131, 258.
|| 12. 1943. "Distribution of nucleic acid in the cell"
NATURE, 152, 503
|| 13. 1944. (with 11.:.Barber) "Distribution of nucleic acid
in the cell ". HATURE, 153, 109.
2.
|| 14. l947.(with G. _'ontalenti) "Chiasma interference in
Mosquitoes". J. Genet., 48,119.
|| 15. 1948. "Alcune proprietĂ fisiche della membrana nucleare ".
Ricercha Scientifica, 18, 1.
|| 16. 1948. "Ribose nucleic acid in the Drosophila egg ".
NATURE, 161, 440.
|| 17. 1949. "Cleavage rate, oxygen consumption and ribose
nucleic acid content of sea urchin eggs ".
Biochem.et Biophys..cta, 3, 92.
|| 18. 1949 (with J.T.Randall,- . .S., and S.G.Tomlin) "An
electron microscope study of the nuclear membrane"
NATURE, 163, 280.
|| 19. 1949. "Chiasma interference in diploid, tetraploid and
interchange spermatocytes of the earwig ".
J. Genet. 49, 209.
|| 20. 1950 (with H.Spurway) "Hybrids between some members of
the Rassenkreis Triturus cristatus ".
EXPERIENTIA, in press.
|| 21. 1950 (wroth H.Spurway) "A study of meiosis in interracial hybrids of the newt Triturus cristatus ".
J. Genet. in press.
|| 22. 1950 (with GiL.Brown and G.Leaf) "The chemical nature
of nuclear sap ". NATURE, in press.
|| 23. 1950 (with S.G.Tornlin) "Experimental studies on
amphibian oocyte nuclei.l. Invettigation of the
structure of the nuclear membrane by means of
the electron microscope". Proc.roy.Soc.B, in pres
Orbital transfer vehicle concept definition and system analysis study, 1985. Volume 3: System and program trades
The key system and program trade studies performed to arrive at a preferred Orbital Transfer Vehicle (OTV) system concept and evolutionary approach to the acquisition of the requisite capabilites is documented. These efforts were expanded to encompass a Space Transportation Architecture Study (STAS) mission model and recommended unmanned cargo vehicle. The most important factors affecting the results presented are the mission model requirements and selection criteria. The reason for conducting the OTV concept definition and system analyses study is to select a concept and acquisition approach that meets a delivery requirement reflected by the mission model
On T-duality for open strings in general abelian and nonabelian gauge field backgrounds
We discuss T-duality for open strings in general background fields both in
the functional integral formulation as well as in the language of canonical
transformations. The Dirichlet boundary condition in the dual theory has to be
treated as a constraint on the functional integration. Furthermore, we give
meaning to the notion of matrix valued string end point position in the
presence of nonabelian gauge field background.Comment: 10 pages, Latex, an inconsistency of the notation in section 3 is
removed, 2 references adde
Boundary susceptibility in the spin-1/2 chain: Curie like behavior without magnetic impurities
We investigate the low-temperature thermodynamics of the spin-1/2 Heisenberg
chain with open ends. On the basis of boundary conformal field theory arguments
and numerical density matrix renormalization group calculations, it is
established that in the isotropic case the impurity susceptibility exhibits a
Curie-like divergent behavior as the temperature decreases, even in the absence
of magnetic impurities. A similar singular temperature dependence is also found
in the boundary contributions of the specific heat coefficient. In the
anisotropic case, for , these boundary quantities still show
singular temperature dependence obeying a power law with an anomalous
dimension. Experimental consequences will be discussed.Comment: 5 pages, 1 figure, final versio
Low-Lying Dirac Eigenmodes, Topological Charge Fluctuations and the Instanton Liquid Model
The local structure of low-lying eigenmodes of the overlap Dirac operator is
studied. It is found that these modes cannot be described as linear
combinations of 't Hooft "would-be" zeromodes associated with instanton
excitations that underly the Instanton Liquid Model. This implies that the
instanton liquid scenario for spontaneous chiral symmetry breaking in QCD is
not accurate. More generally, our data suggests that the vacuum fluctuations of
topological charge are not effectively dominated by localized lumps of unit
charge with which the topological "would-be" zeromodes could be associated.Comment: Presented by I. Horvath at the NATO Advanced Research Workshop
"Confinement, Topology, and other Non-Perturbative Aspects of QCD", January
21-27, 2002, Stara Lesna, Slovakia. 12 pages, 6 figures, uses crckapb.st
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