95 research outputs found
On the presence of mid-gap states in CaV4O9
Using exact diagonalizations of finite clusters with up to 32 sites, we study
the model on the 1/5 depleted square lattice. Spin-spin correlation
functions are consistent with plaquette order in the spin gap phase which
exists for intermediate values of . Besides, we show that singlet
states will be present in the singlet-triplet gap if is not too small
(). We argue that this property should play a central
role in determining the exchange integrals in Comment: 4 pages, 5 postscript figure
NaV_2O_5 as a quarter-filled ladder compound
A new X-ray diffraction study of the one-dimensional spin-Peierls compound
\alpha-NaV_2O_5 reveals a centrosymmetric (Pmmn) crystal structure with one
type of V site, contrary to the previously postulated non-centrosymmetric
P2_1mn structure with two types of V sites (V^{+4} and V^{+5}). Density
functional calculations indicate that NaV_2O_5 is a quarter-filled ladder
compound with the spins carried by V-O-V molecular orbitals on the rungs of the
ladder. Estimates of the charge-transfer gap and the exchange coupling agree
well with experiment and explain the insulating behavior of NaV_2O_5 and its
magnetic properties.Comment: Final version for PRL, value of U correcte
Sr2V3O9 and Ba2V3O9: quasi one-dimensional spin-systems with an anomalous low temperature susceptibility
The magnetic behaviour of the low-dimensional Vanadium-oxides Sr2V3O9 and
Ba2V3O9 was investigated by means of magnetic susceptibility and specific heat
measurements. In both compounds, the results can be very well described by an
S=1/2 Heisenberg antiferromagnetic chain with an intrachain exchange of J = 82
K and J = 94 K in Sr2V3O9 and Ba2V3O9, respectively. In Sr2V3O9,
antiferromagnetic ordering at T_N = 5.3 K indicate a weak interchain exchange
of the order of J_perp ~ 2 K. In contrast, no evidence for magnetic order was
found in Ba2V3O9 down to 0.5 K, pointing to an even smaller interchain
coupling. In both compounds, we observe a pronounced Curie-like increase of the
susceptibility below 30 K, which we tentatively attribute to a staggered field
effect induced by the applied magnetic field. Results of LDA calculations
support the quasi one-dimensional character and indicate that in Sr2V3O9, the
magnetic chain is perpendicular to the structural one with the magnetic
exchange being transferred through VO4 tetrahedra.Comment: Submitted to Phy. Rev.
Local Government's effective community responses
Speech given at the conference 'Reducing criminality: partnerships and best practice', Perth, 31 July to 1 August 2000, by Adam Graycar, Director, Australian Institute of Criminology. This speech is made available under the CC-BY-NC-ND 4.0 license: http://creativecommons.org/licenses/by-nc-nd/4.0/The challenge before us is to find the right set of interventions to prevent criminal behaviour among young people, and prevent that behaviour becoming a lifelong activity. The two main strategies are on the one hand to reduce the supply of motivated offenders, and on the other to make crime more difficult to commit. Crime is the result of complex changes in economic, social and cultural factors such as unemployment, dysfunctional families, child abuse, poor education, community breakdown, economic inequality and substance abuse. If crime prevention is to succeed it should focus on broad social outcomes, for example reducing social exclusion. Compelling evidence suggests that those who feel excluded from participation in community life are more likely to offend against that community. Addressing this sense of exclusion can reduce the risk of offending. In simple terms the criminal justice domain plays only a small part in crime prevention and preventing the supply of motivated offenders
Dysnatremia is a predictor for morbidity and mortality in hospitalized patients with COVID-19
Context:
Dysnatremia is an independent predictor of mortality in patients with bacterial pneumonia. There is paucity of data about the incidence and prognostic impact of abnormal sodium concentration in patients with coronavirus disease 2019 (COVID-19).
Objective:
This work aimed to examine the association of serum sodium during hospitalization with key clinical outcomes, including mortality, need for advanced respiratory support and acute kidney injury (AKI), and to explore the role of serum sodium as a marker of inflammatory response in COVID-19.
Methods:
This retrospective longitudinal cohort study, including all adult patients who presented with COVID-19 to 2 hospitals in London over an 8-week period, evaluated the association of dysnatremia (serum sodium  145 mmol/L, hyponatremia, and hypernatremia, respectively) at several time points with inpatient mortality, need for advanced ventilatory support, and AKI.
Results:
The study included 488 patients (median age, 68 years). At presentation, 24.6% of patients were hyponatremic, mainly due to hypovolemia, and 5.3% hypernatremic. Hypernatremia 2 days after admission and exposure to hypernatremia at any time point during hospitalization were associated with a 2.34-fold (95% CI, 1.08-5.05; P = .0014) and 3.05-fold (95% CI, 1.69-5.49; P < .0001) increased risk of death, respectively, compared to normonatremia. Hyponatremia at admission was linked with a 2.18-fold increase in the likelihood of needing ventilatory support (95% CI, 1.34-3.45, P = .0011). Hyponatremia was not a risk factor for in-hospital mortality, except for the subgroup of patients with hypovolemic hyponatremia. Sodium values were not associated with the risk for AKI and length of hospital stay.
Conclusion:
Abnormal sodium levels during hospitalization are risk factors for poor prognosis, with hypernatremia and hyponatremia being associated with a greater risk of death and respiratory failure, respectively. Serum sodium values could be used for risk stratification in patients with COVID-19
New Method to Calculate the Sign and Relative Strength of Magnetic Interactions in Low-Dimensional Systems on the Basis of Structural Data
The connection of strength of magnetic interactions and type ordering the
magnetic moments with crystal chemical characteristics in low-dimensional
magnets is investigated. The new method to calculate the sign and relative
strength of magnetic interactions in low-dimensional systems on the basis of
the structural data is proposed. This method allows to estimate magnetic
interactions not only inside low-dimensional fragments but also between them,
and also to predict the possibility of the occurrence of magnetic phase
transitions and anomalies of the magnetic interactions. Moreover, it can be
used for search of low-dimensional magnets among the compounds whose crystal
structures are known. The possibilities of the method are illustrated in an
example of research of magnetic interactions in familiar low-dimensional
magnets SrCu2(BO3)2, CaCuGe2O6, CaV4O9, Cu2Te2O5Cl2, Cu2Te2O5Br2, BaCu2Si2O7,
BaCu2Ge2O7, BaCuSi2O6, LiCu2O2, and NaCu2O2.Comment: 18 pages, 8 figures, 2 tables, published versio
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