18,220 research outputs found
An examination of the IFS corporation tax forecasting record
This paper examines the corporation tax forecasting techniques used by the
Institute for Fiscal Studies. For current year forecasts a judgemental forecast is
found to have performed better than relying solely on a simple model or
information on the receipts available so far in the current financial year. For
longer time horizons the judgemental forecast has performed slightly less well
than the modelled forecast. While forecasts made later in the financial year have
led to more accurate estimates of receipts in the current year no evidence is
found that this has improved the accuracy of longer run forecasts. In the short
term inaccuracies in the modelling process are found to be more important than
errors in forecasting growth in corporate profits. However the latter is still an
important component of errors and one that grows substantially in relative
importance as the forecast horizon increases
Super Rogers-Szeg\"o polynomials associated with type of Polychronakos spin chains
As is well known, multivariate Rogers-Szeg\"o polynomials are closely
connected with the partition functions of the type of Polychronakos
spin chains having long-range interactions. Applying the `freezing trick', here
we derive the partition functions for a class of type of Polychronakos
spin chains containing supersymmetric analogues of polarized spin reversal
operators and subsequently use those partition functions to obtain novel
multivariate super Rogers-Szeg\"o (SRS) polynomials depending on four types of
variables. We construct the generating functions for such SRS polynomials and
show that these polynomials can be written as some bilinear combinations of the
type of SRS polynomials. We also use the above mentioned generating
functions to derive a set of recursion relations for the partition functions of
the type of Polychronakos spin chains involving different numbers of
lattice sites and internal degrees of freedom.Comment: 33 pages, minor typos corrected, journal reference give
Software for cut-generating functions in the Gomory--Johnson model and beyond
We present software for investigations with cut generating functions in the
Gomory-Johnson model and extensions, implemented in the computer algebra system
SageMath.Comment: 8 pages, 3 figures; to appear in Proc. International Congress on
Mathematical Software 201
On the Power-Law Tail in the Mass Function of Protostellar Condensations and Stars
We explore the idea that the power-law tail in the mass function of
protostellar condensations and stars arises from the accretion of ambient cloud
material on to a condensation, coupled with a nonuniform (exponential)
distribution of accretion lifetimes. This model allows for the generation of
power-law distributions in all star-forming regions, even if condensations
start with a lognormal mass distribution, as may be expected from the central
limit theorem, and supported by some recent numerical simulations of turbulent
molecular clouds. For a condensation mass with growth rate , an analytic three-parameter probability density function is derived; it
resembles a lognormal at low mass and has a pure power-law high-mass tail. An
approximate power-law tail is also expected for other growth laws, and we
calculate the distribution for the plausible case .
Furthermore, any single time snapshot of the masses of condensations that are
still accreting (and are of varying ages) also yields a distribution with a
power-law tail similar to that of the IMF.Comment: 5 pages, 4 figures, to appear in MNRAS (Letters section
Comparison of High-degree Solar Acoustic Frequencies and Asymmetry between Velocity and Intensity Data
Using the local helioseismic technique of ring diagram we analyze the
frequencies of high--degree f- and p-modes derived from both velocity and
continuum intensity data observed by MDI. Fitting the spectra with asymmetric
peak profiles, we find that the asymmetry associated with velocity line
profiles is negative for all frequency ranges agreeing with previous
observations while the asymmetry of the intensity profiles shows a complex and
frequency dependent behavior. We also observe systematic frequency differences
between intensity and velocity spectra at the high end of the frequency range,
mostly above 4 mHz. We infer that this difference arises from the fitting of
the intensity rather than the velocity spectra. We also show that the frequency
differences between intensity and velocity do not vary significantly from the
disk center to the limb when the spectra are fitted with the asymmetric profile
and conclude that only a part of the background is correlated with the
intensity oscillations.Comment: Accepted for publication in Astrophysical Journa
A Mass Formula from Light to Hypernuclei
Simultaneous description of ordinary and hypernuclei masses by a single mass
formula has been a great challenge in nuclear physics. Hyperon-separation
energies of about forty Lambda(), three
Lambda-Lambda(), one Sigma() and seven Cascade()
hypernuclei have been experimentally found. Many of these nuclei are of light
masses. We prescribe a new mass formula, called BWMH, which describes the
normal and hypernuclei on the same footing. It is based on the
modified-Bethe-Weizs\"acker mass formula (BWM). BWM is basically an extension
of the Bethe-Weizs\"acker mass formula (BW) for light nuclei. The parameters of
BWM were optimized by fitting about 3000 normal nuclei available recently. The
original Bethe-Weizs\"acker mass formula (BW) was designed for medium and heavy
mass nuclei and it fails for light nuclei. Two earlier works on hypernuclei
based on this BW show some limitations. The BWMH gives improved agreement with
the experimental data for the line of stability, one-neutron separation energy
versus neutron number spectra of normal nuclei, and the hyperon-separation
energies from hypernuclei. The drip lines are modified for addition of a
hyperon in a normal nucleus.Comment: Presented at the "XXIX Mazurian Lakes Conference on Physics: Nuclear
Physics and the Fundamental Processes, Piaski, Poland, August 30 - September
6, 2005." (7 pages, 1 Table, 1 Figure
Isobaric incompressibility of the isospin asymmetric nuclear matter
The isospin dependence of the saturation properties of asymmetric nuclear
matter, particularly the incompressibility at saturation density is systematically studied using density
dependent M3Y interaction. The characterizes the isospin dependence of
the incompressibility at saturation density . The approximate
expression is often used for where
and represent, respectively, the slope and curvature parameters of
the symmetry energy at . It can be expressed accurately as
where is the third-order
derivative parameter of symmetric nuclear matter at . The results of
this addendum to Phys. Rev. C 80, 011305(R) (2009) indicate that the
contribution to is not insignificant.Comment: 4 pages including 1 table and 1 figur
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