2,182 research outputs found
Breakdown of the perturbative renormalization group for S >= 1 random antiferromagnetic spin chains
We investigate the application of a perturbative renormalization group (RG)
method to random antiferromagnetic Heisenberg chains with arbitrary spin size.
At zero temperature we observe that initial arbitrary probability distributions
develop a singularity at J=0, for all values of spin S. When the RG method is
extended to finite temperatures, without any additional assumptions, we find
anomalous results for S >= 1. These results lead us to conclude that the
perturbative scheme is not adequate to study random chains with S >= 1.
Therefore a random singlet phase in its more restrictive definition is only
assured for spin-1/2 chains.Comment: 5 pages, 3 figures. To appear in Physical Review
Phase transitions in the two-dimensional super-antiferromagnetic Ising model with next-nearest-neighbor interactions
We use Monte Carlo and Transfer Matrix methods in combination with
extrapolation schemes to determine the phase diagram of the 2D
super-antiferromagnetic (SAF) Ising model with next-nearest-neighbor (nnn)
interactions in a magnetic field. The interactions between nearest-neighbor
(nn) spins are ferromagnetic along x, and antiferromagnetic along y. We find
that for sufficiently low temperatures and fields, there exists a region
limited by a critical line of 2nd-order transitions separating a SAF phase from
a magnetically induced paramagnetic phase. We did not find any region with
either first-order transition or with re-entrant behavior. The nnn couplings
produce either an expansion or a contraction of the SAF phase. Expansion occurs
when the interactions are antiferromagnetic, and contraction when they are
ferromagnetic. There is a critical ratio R_c = 1/2 between nnn- and
nn-couplings, beyond which the SAF phase no longer exists.Comment: 12 pages, 10 figure
Bacterial colonization of seston particles in brackish waters (Ria de Aveiro, Portugal)
The frequency of attached bacteria, as percentage of total bacteria, in estuarine water of
the Ria de Aveiro was determined over a seasonal range of temperature, seston, BOD, salinity and
water depth. The frequency was inversely related to temperature only in the marine zone of the lagoon.
No other associations could be established with environmental factors The broad spring-summer peak
of total bacteria was not apparent in attached bacteria which showed an erratic temporal profile with an average frequency of 9 % (range 1 to 49 %] of total planktonic bacteria The bacterial coverage per unit area of particle surface was densest in small particles The density of coverage decreased sharply to values corresponding to 22,5 and 2 % in particles > 3 to 10, > l0 to 40 and > 40 to 140 pm in diameter respecitvely compared to the density of coverage of the > 1 to 3 pm size-class Colonized seston and sediment particles exhibited similar bacterial numbers per particle of each size-class and did not show tidal spatial 01 seasonal patterns of variation it is suggested that bacteria only seldom attach to particles in the water column of this lagoon and that resuspension of bottom sediments is the main factor governing the frequency of colonized particles in surface water
The Economy and Demographics of Lea County and the Larger Region: Report to the Lea County Community Improvement Corporation
This set of reports examines economic and demographic developments in Lea County, New Mexico, and the larger region of southeastern New Mexico and west Texas. The major objective was to develop a new forecast for the economy of Lea County within the context of the larger region and to develop new population estimates and projections that reflect the changes occurring within the region. There are four documents in the series: Executive Summary; the Economy of Lea County and the Larger Region; Survey of Lea County Employers; and Population, Housing and Education in Lea County
Variability of nutrients and chlorophyll a in Ancao Inlet during a spring tidal cycle in April 2009
Sao Luis or Ancao Inlet is the most western of the six inlets of the Ria Formosa lagoon, in southern Portugal. This inlet contributes relatively little to the water volume exchange over a tidal cycle (similar to 10%). Temperature, salinity, pH, dissolved oxygen, and chlorophyll a and nutrient concentrations were measured hourly at the surface, at an intermediate level, and near the bottom over a complete spring tidal cycle, at a sampling point in the middle of the inlet. Current velocity was also measured hourly over the entire cross-section of the inlet using an acoustic Doppler current meter. From these parameters, the flow rate and the transport of nutrients and chlorophyll a were calculated and integrated over the complete tidal cycle providing the net transport. The results show that this is a well-mixed dynamic inlet where, during spring tide, the tidal signal is evident particularly for the nutrient and chlorophyll a concentrations. The nutrient concentrations were low (almost depleted), while the chlorophyll a concentrations were high (4-6 mg m(-3)). The estimated transports through Ancao Inlet revealed that there was a net import of chlorophyll a, nitrate, and phosphate to the Ria Formosa lagoon, while silicate was exported to the adjacent coastal area.Center for Marine and Environmental Research (CIMA, Portugal)info:eu-repo/semantics/publishedVersio
Master Operators Govern Multifractality in Percolation
Using renormalization group methods we study multifractality in percolation
at the instance of noisy random resistor networks. We introduce the concept of
master operators. The multifractal moments of the current distribution (which
are proportional to the noise cumulants of the
resistance between two sites x and located on the same cluster) are
related to such master operators. The scaling behavior of the multifractal
moments is governed exclusively by the master operators, even though a myriad
of servant operators is involved in the renormalization procedure. We calculate
the family of multifractal exponents for the scaling behavior of the
noise cumulants, ,
where is the correlation length exponent for percolation, to two-loop
order.Comment: 6 page
Yield and Quality Parameters of an Interspecific Hybrid \u3cem\u3ePennisetum Purpureum\u3c/em\u3e Schum. (Elephant-Grass) \u3cem\u3eX Pennisetum Glaucum\u3c/em\u3e (L.) R. Br. Stuntz (Pearl Millet)
Elephant-grass is a tropical forage grass used either as a supplement fodder or for direct grazing. It usually shows regular nutritive value (6-13% crude protein, CP, and 55-60% forage digestibility) (Alcantara et al., 1981). Most of the available cultivars produce no viable seeds. On the other hand, pearl millet has high seed yielding potential along with high quality forage (\u3e15% CP and 70% forage digestibility). However, it shows poor forage production, low field persistence under grazing and low regrowth potential after cutting or grazing. During the 90\u27s, an interspecific hybrid between the two species was developed, trying to combine the elephant-grass adaaptability and forage yielding potential with the pearl millet forage quality and seed yielding potential (Schank et al., 1993; Schank, 1996). The new genetic material was able to produce viable seeds in variable amounts (Diz et al., 1995). The main aim of this research was to produce selected populations with high phenotypic uniformities, showing high average forage production and quality
Critical Analysis of Tropical Forage Breeding in Brazil
Forage grasses account for 90% of the Brazilian forage seed market while the genera Brachiaria, Panicum and others are responsible for 85, 10 and 5% of the traded grass seeds, respectively. Most of the forage grass and legume cultivars available for sowing in Brazil were selected in germplasm banks during the last 20 years, while few of them were derived from artificial crossings, followed by selection for desirable forage traits. The selection of new genetic materials in germplasm banks (exploitation of naturally-occurring genetic variability) is still feasible but the chances of success are decreasing through time. From now on, a clear trend is becoming quite evident: the exploitation of new genetic variation, to be accomplished through artificial crossings between selected parentals, in each forage species, aiming at the synthesis, selection and releasing of new hybrids showing high field performance
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