1,585 research outputs found
A provisional survey of the interaction between net photosynthetic rate, respiratory rate, and thallus water content in some New Zealand cryptogams
The effect of water content on photosynthetic and respiratory rates in eight lichen species and one bryophyte species were studied using an injection infrared gas analyser technique. All species snowed a strong relationship between net assimilation rate (NAR), respiration rate, and water content similar to relationships reported in published studies overseas. Species from moist habitats showed negative NAR at low water contents. Species from high-light areas showed a depression in NAR at high water contents which could be alleviated by higher light intensities. The experiments confirmed the suitability of New Zealand species for these studies
On-disc observations of flux rope formation prior to its eruption
Coronal mass ejections (CMEs) are one of the primary manifestations of solar activity and can drive severe space weather effects. Therefore, it is vital to work towards being able to predict their occurrence. However, many aspects of CME formation and eruption remain unclear, including whether magnetic flux ropes are present before the onset of eruption and the key mechanisms that cause CMEs to occur. In this work, the pre-eruptive coronal configuration of an active region that produced an interplanetary CME with a clear magnetic flux rope structure at 1 AU is studied. A forward-S sigmoid appears in extreme-ultraviolet (EUV) data two hours before the onset of the eruption (SOL2012-06-14), which is interpreted as a signature of a right-handed flux rope that formed prior to the eruption. Flare ribbons and EUV dimmings are used to infer the locations of the flux rope footpoints. These locations, together with observations of the global magnetic flux distribution, indicate that an interaction between newly emerged magnetic flux and pre-existing sunspot field in the days prior to the eruption may have enabled the coronal flux rope to form via tether-cutting-like reconnection. Composition analysis suggests that the flux rope had a coronal plasma composition, supporting our interpretation that the flux rope formed via magnetic reconnection in the corona. Once formed, the flux rope remained stable for two hours before erupting as a CME
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LBL Magnetic-Measurements Data-Acquisition System
The LBL Magnetic Measurements Engineering (MME) Group has developed a Real-Time Data Acquisition System (DAS) for magnetic measurements. The design objective was for a system that was versatile, portable, modular, expandable, quickly and easily reconfigurable both in hardware and software, and inexpensive. All objectives except the last were attained. An LSI 11/23 microcomputer is interfaced to a clock-calendar, printer, CRT control terminal, plotter with hard copy, floppy and hard disks, GPIB, and CAMAC buses. Off-the-shelf hardware and software have been used where possible. Operational capabilities include: (1) measurement of high permeability materials; (2) harmonic error analysis of (a) superconducting dipoles and (b) rare earth cobalt (REC) and conventional quadrupole magnets; and (3) 0.1% accuracy x-y mapping with Hall probes. Results are typically presented in both tabular and graphical form during measurements. Only minutes are required to switch from one measurement capability to another. Brief descriptions of the DAS capabilities, some of the special instrumentation developed to implement these capabilities, and planned developments are given below
The Box Graph In Superstring Theory
In theories of closed oriented superstrings, the one loop amplitude is given
by a single diagram, with the topology of a torus. Its interpretation had
remained obscure, because it was formally real, converged only for purely
imaginary values of the Mandelstam variables, and had to account for the
singularities of both the box graph and the one particle reducible graphs in
field theories. We present in detail an analytic continuation method which
resolves all these difficulties. It is based on a reduction to certain minimal
amplitudes which can themselves be expressed in terms of double and single
dispersion relations, with explicit spectral densities. The minimal amplitudes
correspond formally to an infinite superposition of box graphs on
like field theories, whose divergence is responsible for the poles in the
string amplitudes. This paper is a considerable simplification and
generalization of our earlier proposal published in Phys. Rev. Lett. 70 (1993)
p 3692.Comment: Plain TeX, 67 pp. and 9 figures, Columbia/UCLA/94/TEP/3
Higher order curvature generalisations of Bartnick-McKinnon and coloured black hole solutions in
We construct globally regular as well as non-abelian black hole solutions of
a higher order curvature Einstein-Yang-Mills (EYM) model in dimensions.
This model consists of the superposition of the first two members of the
gravitational hierarchy (Einstein plus first Gauss-Bonnet(GB)) interacting with
the superposition of the first two members of the Yang--Mills
hierarchy.Comment: 13 Revtex pages, 5 PS figures; discussions extended, reference adde
A no-go for no-go theorems prohibiting cosmic acceleration in extra dimensional models
A four-dimensional effective theory that arises as the low-energy limit of
some extra-dimensional model is constrained by the higher dimensional Einstein
equations. Steinhardt & Wesley use this to show that accelerated expansion in
our four large dimensions can only be transient in a large class of
Kaluza-Klein models that satisfy the (higher dimensional) null energy condition
[1]. We point out that these no-go theorems are based on a rather ad-hoc
assumption on the metric, without which no strong statements can be made.Comment: 20 page
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AC magnetic measurements of the ALS Booster Dipole Engineering Model Magnet
10 Hz sine wave and 2 Hz sawtooth AC magnetic measurements of he curved ALS Booster Dipole Engineering Model Magnet have been accomplished. Long curved coils were utilized to measure the integral transfer function and uniformity. Point coils and a Hall Probe were used to measure magnetic induction and its uniformity. The data were logged and processed by a Tektronix 11401 digital oscilloscope. The dependence of the effective length on the field was determined from the ratio of the integral coil signals to the point coil signals. Quadrupole and sextupole harmonics were derived from the point and integral uniformity measurements. 5 refs., 4 figs., 2 tabs
Two-Loop Superstrings II, The Chiral Measure on Moduli Space
A detailed derivation from first principles is given for the unambiguous and
slice-independent formula for the two-loop superstring chiral measure which was
announced in the first paper of this series. Supergeometries are projected onto
their super period matrices, and the integration over odd supermoduli is
performed by integrating over the fibers of this projection. The subtleties
associated with this procedure are identified. They require the inclusion of
some new finite-dimensional Jacobian superdeterminants, a deformation of the
worldsheet correlation functions using the stress tensor, and perhaps
paradoxically, another additional gauge choice, ``slice \hat\mu choice'', whose
independence also has to be established. This is done using an important
correspondence between superholomorphic notions with respect to a supergeometry
and holomorphic notions with respect to its super period matrix. Altogether,
the subtleties produce precisely the corrective terms which restore the
independence of the resulting gauge-fixed formula under infinitesimal changes
of gauge-slice. This independence is a key criterion for any gauge-fixed
formula and hence is verified in detail.Comment: 64 pages, no figure
Two-Loop Superstrings VII, Cohomology of Chiral Amplitudes
The relation between superholomorphicity and holomorphicity of chiral
superstring N-point amplitudes for NS bosons on a genus 2 Riemann surface is
shown to be encoded in a hybrid cohomology theory, incorporating elements of
both de Rham and Dolbeault cohomologies. A constructive algorithm is provided
which shows that, for arbitrary N and for each fixed even spin structure, the
hybrid cohomology classes of the chiral amplitudes of the N-point function on a
surface of genus 2 always admit a holomorphic representative. Three key
ingredients in the derivation are a classification of all kinematic invariants
for the N-point function, a new type of 3-point Green's function, and a
recursive construction by monodromies of certain sections of vector bundles
over the moduli space of Riemann surfaces, holomorphic in all but exactly one
or two insertion points.Comment: 103 pages, 2 figure
Two-Loop Superstrings I, Main Formulas
An unambiguous and slice-independent formula for the two-loop superstring
measure on moduli space for even spin structure is constructed from first
principles. The construction uses the super-period matrix as moduli invariant
under worldsheet supersymmetry. This produces new subtle contributions to the
gauge-fixing process, which eliminate all the ambiguities plaguing earlier
gauge-fixed formulas.
The superstring measure can be computed explicitly and a simple expression in
terms of modular forms is obtained. For fixed spin structure, the measure
exhibits the expected behavior under degenerations of the surface. The measure
allows for a unique modular covariant GSO projection. Under this GSO
projection, the cosmological constant, the 1-, 2- and 3- point functions of
massless supergravitons all vanish pointwise on moduli space without the
appearance of boundary terms. A certain disconnected part of the 4-point
function is shown to be given by a convergent, finite integral on moduli space.
A general slice-independent formula is given for the two-loop cosmological
constant in compactifications with central charge c=15 and N=1 worldsheet
supersymmetry in terms of the data of the compactification conformal field
theory.
In this paper, a summary of the above results is presented with detailed
constructions, derivations and proofs to be provided in a series of subsequent
publications.Comment: 21 pages, no figures, references added, minor typos correcte
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