1,789 research outputs found
From Quasars to Extraordinary N-body Problems
We outline reasoning that led to the current theory of quasars and look at
George Contopoulos's place in the long history of the N-body problem. Following
Newton we find new exactly soluble N-body problems with multibody forces and
give a strange eternally pulsating system that in its other degrees of freedom
reaches statistical equilibrium.Comment: 13 pages, LaTeX with 1 postscript figure included. To appear in
Proceedings of New York Academy of Sciences, 13th Florida Workshop in
Nonlinear Astronomy and Physic
Sensitive Observations of Radio Recombination Lines in Orion and W51: The Data and Detection of Systematic Recombination Line Blueshifts Proportional to Impact Broadening
Sensitive spectral observations made in two frequency bands near 6.0 and 17.6
GHz are described for Orion and W51. Using frequency switching we were able to
achieve a dynamic range in excess of 10,000 without fitting sinusoidal or
polynomial baselines. This enabled us to detect lines as weak as T\Delta n$ as
high as 25 have been detected in Orion. In the Orion data, where the lines are
stronger, we have also detected a systematic shift in the line center
frequencies proportional to linewidth that cannot be explained by normal
optical depth effects.Comment: 22 pages, 13 figures. Accepted for publication in Astrophysics and
Space Scienc
Effects of rundown in soil hydraulic condition on crop productivity in south-eastern Queensland - a simulation study
Declining soil organic matter levels because of cropping have been shown to reduce crop growth and yield, but the effects of changing infiltration and soil hydraulic properties on crop productivity have not been widely evaluated. Cropping systems in south-eastern Queensland have, in the past, involved intense tillage, trafficking with heavy machinery, and changed organic matter cycling, affecting soil aggregation, permeability, water-holding characteristics, and organic matter. The aim of this paper is to determine how important infiltration and soil hydraulic condition has been to the water balance, crop growth, and yield in the past, and may be in the future if management is not changed. Change in physical and chemical condition of the 5 most commonly cropped soils in south-east Queensland (Sodosols, Vertosols with â€55% clay, Vertosols with >55% clay, Red Ferrosols and Red Chromosols/Kandosols) was measured over 0â70 years of cropping and estimated up to 200 years. The APSIM model was used to predict effects of changing soil condition in a rain-fed, fertilised, wheat-summer fallow cropping system with intense tillage. Decline in infiltration, restricted internal redistribution of water, and increased evaporation reduced water supply to the crop, causing simulated yield to decline by 29, 38, 25, 17, and 13% for the 5 soils, respectively, after 50 years of cropping. Gross margin declined at a faster rate, falling by 36, 50, 40, 20, and 21%, respectively after 50 years because of increasing fertiliser requirement to compensate for declining soil fertility. Crop productivity on most soils continued to steadily decline as period of cropping increased to 200 years. To arrest or reverse this downward trend, it is likely that substantial changes to current cropping systems will be needed, including reducing tillage and trafficking, and improving organic matter levels
Particle Acceleration at Relativistic Shocks
I review the current status of Fermi acceleration theory at relativistic
shocks. I first discuss the relativistic shock jump conditions, then describe
the non-relativistic Fermi mechanism and the differences introduced by
relativistic flows. I present numerical calculations of the accelerated
particle spectrum, and examine the maximum energy attainable by this process. I
briefly consider the minimum energy for Fermi acceleration, and a possible
electron pre-acceleration mechanism.Comment: 17 pages, 4 figures. To appear in "Relativistic Flows in
Astrophysics", A.W. Guthmann, M. Georganopoulos, A. Marcowith and K.
Manolokou, eds., Lecture Notes in Pysics, Springer Verla
Simulating infiltration and the water balance in cropping systems with APSIM-SWIM
We test APSIM-SWIM's ability to simulate infiltration and interactions between the soil water balance and grain crop growth using soil hydraulic properties derived from independent, point measurements. APSIMSWIM is a continuous soil-crop model that simulates infiltration, surface crusting, and soil condition in more detail than most other soil-crop models. Runoff, soil water, and crop growth information measured at sites in southern Queensland was used to test the model. Parameter values were derived directly from soil hydraulic properties measured using rainfall simulators, disc permeameters and ponded rings, and pressure plate apparatus. In general, APSIM-SWIM simulated infiltration, runoff, soil water and the water balance, and yield as accurately and reliably as other soil crop models, indicating the model is suitable for evaluating effects of infiltration and soil-water relations on crop growth. Increased model detail did not hinder application, instead improving parameter transferability and utility, but improved methods of characterising crusting, soil hydraulic conductivity, and macroporosity under field conditions would improve ease of application, prediction accuracy, and reliability of the model. Model utility and accuracy would benefit from improved representation of temporal variation in soil condition, including effects of tillage and consolidation on soil condition and bypass flow in cracks
The role of screening blood tests in patients with arterial disease attending vascular outpatients
Objective:to evaluate the benefits of a policy of performing screening blood tests in new patients with arterial disease referred to the vascular outpatients department.Methods:clinical audit over a 12-month period of all new referrals with arterial disease to the vascular outpatients department at the Leicester General Hospital.Results:two hundred and seventy-two patients had at least one blood test performed at their outpatient visit. All of these patients had a full blood count performed, of which 21 results (21%) were abnormal. Further investigation of patients with abnormal results revealed one case of bladder cancer, one case of leukaemia and one patient with polycythaemia. Urea and electrolytes were measured in 269 patients (99%). Of these, 26 (10%) were expectedly abnormal in patients with known renal impairment. A further 27 patients (10%) were identified to have some degree of unrecognised renal impairment. Serum non-fasting glucose was measured in 252 patients (93%). There were 11 unexpectedly raised results, but further investigation of these patients only diagnosed one of these patients as diabetic. Serum cholesterol was measured in 201 patients (74%). One hundred and thirty-two patients (66%) had an abnormally raised serum cholesterol level. Of these, only 12 patients (6%) were known to have hyperlipidaemia.Conclusions:screening new patients with arterial disease in vascular outpatients does identify significant abnormalities, in particular renal impairment and hyperlipidaemia. Correction of these abnormalities may reduce the morbidity associated with contrast induced nephrotoxic acute renal failure, and also contribute to secondary prevention of vascular events associated with raised lipids
The Point of Origin of the Radio Radiation from the Unresolved Cores of Radio-Loud Quasars
Locating the exact point of origin of the core radiation in active galactic
nuclei (AGN) would represent important progress in our understanding of
physical processes in the central engine of these objects. However, due to our
inability to resolve the region containing both the central compact object and
the jet base, this has so far been difficult. Here, using an analysis in which
the lack of resolution does not play a significant role, we demonstrate that it
may be impossible even in most radio loud sources for more than a small
percentage of the core radiation at radio wavelengths to come from the jet
base. We find for 3C279 that percent of the core flux at 15 GHz must
come from a separate, reasonably stable, region that is not part of the jet
base, and that then likely radiates at least quasi-isotropically and is
centered on the black hole. The long-term stability of this component also
suggests that it may originate in a region that extends over many Schwarzschild
radii.Comment: 7 pages with 3 figures, accepted for publication in Astrophysics and
Space Scienc
Three-slit experiments and quantum nonlocality
An interesting link between two very different physical aspects of quantum
mechanics is revealed; these are the absence of third-order interference and
Tsirelson's bound for the nonlocal correlations. Considering multiple-slit
experiments - not only the traditional configuration with two slits, but also
configurations with three and more slits - Sorkin detected that third-order
(and higher-order) interference is not possible in quantum mechanics. The EPR
experiments show that quantum mechanics involves nonlocal correlations which
are demonstrated in a violation of the Bell or CHSH inequality, but are still
limited by a bound discovered by Tsirelson. It now turns out that Tsirelson's
bound holds in a broad class of probabilistic theories provided that they rule
out third-order interference. A major characteristic of this class is the
existence of a reasonable calculus of conditional probability or, phrased more
physically, of a reasonable model for the quantum measurement process.Comment: 9 pages, no figur
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