bluuebunny/crossref_metadata_2025_split huggingface dataset:
Magnetic properties of pure deuteronium and diamagnetically-doped hydronium iron jarosite
Authors: Pettigrew K G , Visser D , Harrison A , Nicholson D H , Kilcoyne S H , Manuel P , Murani A P 
Published: April 2011

D3OFe3(SO4)2(OD)6 is a model example of an S = 5/2 Kagome anti-ferromagnet that exhibits unconventional two-dimensional spin-glass properties. We report quasi-elastic neutron-scattering data on D3OFe3(SO4)2(OD)6 derived from three-directional neutron spin-polarization analysis in combination with time-of-flight analysis (Δ E [Formula: see text] 1 meV). At 1.5 K, within the time window of the experiment, only 45% of the total elastic magnetic moment is frozen  a broad magnetic response in Q is still observed at temperatures in excess of ten times the spin-glass freezing temperature. The dc-magnetization measurements on H3OFe3xAlx(SO4)2(OD)6 show that dilution of the magnetic lattice with Al3+ disrupts the spin-glass state. Mössbauer measurements indicate that the Al replaces the Fe ions on the magnetic sites of the Kagome lattice, giving rise to two distinct iron sites with equal occupation levels but different hyperfine fields. PACS Nos.: 75.10N, 75.30C, 75.30H, 75.50L
SrCu2(BO3)2  a two-dimensional spin liquid
Authors: Knetter C , Bühler A , Singh R RP , Müller-Hartmann E , Uhrig G S 
Published: April 2011

We study an extended ShastrySutherland model for SrCu2(BO3)2 and analyze the low-lying parts of the energy spectrum by means of a perturbative unitary transformation based on flow equations. The derivation of the one-magnon dispersion (elementary triplets) is discussed. Additionally, we give a quantitative description (symmetries and energies) of bound states made from two elementary triplets. Our high-order results allow us to fix the model parameters for SrCu2(BO3)2 precisely: J1 = 6.16(10) meV, x := J2/J1 = 0.603(3), J[Formula: see text] =1.3(2) meV. To our knowledge this is the first quantitative treatment of bound states in a true 2D model. PACS Nos.: 75.40Gb, 75.30Kz, 75.50Ee, 75.10Jm
Chiral order of spin-1/2 frustrated quantum spin chains
Authors: Hikihara T , Kaburagi M , Kawamura H 
Published: April 2011

The ordering of the frustrated S = 1/2 XY spin chain with the competing nearest- and next-nearest-neighbor anti-ferromagnetic couplings, J1 and J2, is studied by using the density-matrix renormalization-group method. It is found that besides the well-known spin-fluid and dimer phases the chain exhibits a gapless "chiral" phase characterized by the spontaneous breaking of parity, in which the long-range order parameter is a chirality, κl =SxlSyl+1  Syl Sxl+1, whereas the spin correlation decays algebraically. The dimer phase is realized for 0.33 [Formula: see text] j = J2/J1 [Formula: see text] 1.26 while the chiral phase is realized for j [Formula: see text] 1.26. PACS No.: 75.25
Frustrated order by disorder: The pyrochlore anti-ferromagnet with bond disorder
Authors: Bellier-Castella L , Gingras M JP , Holdsworth P CW , Moessner R 
Published: April 2011

The classical Heisenberg anti-ferromagnet on the pyrochlore lattice is macroscopically and continuously degenerate and the system remains disordered at all temperatures, even in the presence of weak dilution with nonmagnetic ions. We show that, in contrast, weak-bond disorder lifts the ground-state degeneracy in favour of locally collinear spin configurations. We present a proof that for a single tetrahedron the ground state is perfectly collinear but identify two mechanisms that preclude the establishment of a globally collinear state; one due to frustration and the other due to higher order effects. We thus obtain a rugged energy landscape, which is necessary to account for the glassy phenomena found in real systems such as the pyrochlore Y2Mo2O7 recently reported by Booth et al. (Phys. Rev. B: Condens. Matter Mater. Phys. 62, R755 (2000).) to contain a substantial degree of bond disorder. PACS Nos.: 75.10.Hk, 75.40.Mg, 75.40.Gb
Geometric frustration in the mixed layer pnictide oxides
Authors: Enjalran M , Scalettar R T , Kauzlarich S M 
Published: April 2011

We present results from a Monte Carlo investigation of a simple bilayer model with geometrically frustrated interactions similar to those found in the mixed layer pnictide oxides (Sr2Mn3Pn2O2, Pn = As, Sb). Our model is composed of two inequivalent square lattices with nearest-neighbor intralayer and interlayer interactions. We find a ground state composed of two independent Néel-ordered layers when the interlayer exchange is an order of magnitude weaker than the intralayer exchange, as suggested by experiment. We observe this result independent of the number of layers in our model. We find evidence for local orthogonal order between the layers, but it occurs in regions of parameter space that are not experimentally realized. We conclude that frustration caused by nearest-neighbor interactions in the mixed layer pnictide oxides is not sufficient to explain the long-range orthogonal order that is observed experimentally, and that it is likely that other terms (e.g., local anisotropies) in the Hamiltonian are required to explain the magnetic behavior. PACS Nos.: 75.10Hk, 75.40Mg, 75.50-y, 75.25+z
Magnetic ordering and fluctuation in Kagome lattice anti-ferromagnets, Fe and Cr jarosites
Authors: Nishiyama M , Morimoto T , Maegawa S , Inami T , Oka Y 
Published: April 2011

Jarosite family compounds, KFe3(OH)6(SO4)2 (abbreviated to Fe jarosite) and KCr3(OH)6(SO4)2 (Cr jarosite) are typical examples of Heisenberg anti-ferromagnets on the Kagome lattice and have been investigated by means of magnetization and NMR experiments. The susceptibility of Cr jarosite deviates from the CurieWeiss law due to the short-range spin correlation below about 150 K and shows the magnetic transition at 4.2 K, while Fe jarosite has the transition at 65 K. The measured susceptibility fits well with the calculated one on the high-temperature expansion for the Heisenberg anti-ferromagnet on the Kagome lattice. The values of the exchange interactions of Cr jarosite and Fe jarosite are derived to be JCr = 4.9 K and JFe = 23 K, respectively. The 1H-NMR spectra of Fe jarosite suggest that the ordered spin structure is the q = 0 type 120° configuration with +1 chirality. The transition is considered to be caused by a weak single-ion type anisotropy. The spin-lattice relaxation rate, 1/T1, of Fe jarosite in the ordered phase decreases sharply with decreasing temperature and can be well explained by the two-magnon process of spin wave with the anisotropy. PACS No.: 75.25+z
Heavy-fermion behavior of itinerant frustrated systems: β-Mn, Y(Sc)Mn2, and LiV2O4
Authors: Lacroix C 
Published: April 2011

These three metallic systems do not exhibit any magnetic ordering despite experiments showing the existence of localized moments with large anti-ferromagnetic exchange: we propose that this is a direct consequence of the strong geometric frustration since Y(Sc)Mn2 and LiV2O4 have the pyrochlore structure, while β-Mn has a more complicated frustrated structure. Another similarity between these compounds is their very large specific-heat coefficient γ = C/T (420 mJ mol1 K2 for LiV2O4). Several explanations have been proposed for this "3d heavy-fermion behavior", including a 3d-Kondo effect. However, the similarities between the three compounds indicate that frustration plays a big role. We describe a new model in which we take into account the existence of two types of 3d-electrons (localized and itinerant) and a frustrated anti-ferromagnetic exchange between the localized 3d electrons. PACS Nos.: 75.10Hk, 75.50Ee, 75.40Cx, 75.40-s
The foam geometry "paradox"
Authors: Grassia P S , Cilliers J J , Neethling S J 
Published: April 2011

Plateau's rule states that bubble lamellae in a foam meet at equal angles. Attempts to rationalize this rule via a naive "force along a tangent line" argument employing vertex variables are shown to fail, since they do not properly account for bubble volume constraints. Indeed Plateau's rule appears to make a foam system overdetermined, in the sense that there seem to be more constraints than available variables. The resolution of this paradox is that the angle constraints of Plateau's rule cannot be regarded as all independent. This is explained in detail for the two-bubble system in two dimensions. By exploiting just pressure-curvature relations and geometry, it is shown that the lamella joining the two bubbles is obliged to subtend precisely the angle needed to satisfy Plateau's rule and minimize energy. Speculations are offered for a many bubble foam. PACS Nos.: 68.10Cr, 68.15+e
Laser-assisted elastic electron scattering from helium
Authors: Wallbank B , Holmes J K 
Published: April 2011

We report measurements of the differential cross section for scattering of electrons, from helium, with energies in the range 120 eV through scattering angles of 14°140° in the presence of a high-intensity carbon dioxide laser. These results were obtained with beam geometries for which the KrollWatson approximation, normally applied to these types of measurements, predicts zero cross sections. The cross sections reported are not zero but confirm similar experiments with argon as the scattering centre. PACS No.: 34.80Qb
Possible gapless chiral phase in a frustrated S = 1 1D anti-ferromagnet, CaV2O4
Authors: Kikuchi H , Chiba M , Kubo T 
Published: April 2011

We have measured magnetic susceptibility and 51V NMR of CaV2O4, a model substance for a frustrated S = 1 spin chain with competing first- and second-neighbor anti-ferromagnetic interactions. Both the low-temperature magnetic susceptibility and the NMR Knight shift did not go down to zero as the temperature was lowered, suggesting that a spin gap is not present in CaV2O4. The absence of a spin gap gives us a clear contrast to the case of the nonfrustrated spin chains, which should have the Haldane gap. Recently published theoretical results for S = 1 XY or XXZ spin chain indicate that the gapless chiral phase could appear in a relatively broad region. Experimental results are discussed in terms of these theoretical predictions. A spin-freezing anomaly was observed at 20 K, reflecting the spin-frustrating nature of the system. PACS Nos.: 75.30, 75.50
Magnetic susceptibility study of the heavy rare-earth stannate pyrochlores
Authors: Bondah-Jagalu V , Bramwell S T 
Published: April 2011

The series of magnetic rare-earth pyrochlore stannates R2Sn2O7 (R = rare earth, except Ce and Pm) have been investigated by powder susceptibility measurements down to T = 1.8 K. The results are compared with results for the analogous titanate series, which are well known frustrated magnets. Unlike the titanates, the whole series can be formed in the cubic pyrochlore structure. Possible experimental advantages of studying the stannates are discussed. PACS Nos.: 75.10Nr, 75.50Ee, 75.50Lk
The E2 admixtures in mixed multipole lines 459.7 and 564.0 nm of Bi IThis paper was presented at the International Conference on Precision Physics of Simple Atomic Systems, held at University of Windsor, Windsor, Ontario, Canada on 21–26 July 2008.
Authors: Werbowy S. , Kwela J. 
Published: April 2011

Studies of the M1-E2 interference effect in the Zeeman spectra of forbidden lines 459.7 and 564.0 nm of Bi I are reported. By the use of computer modelling techniques, the simulated contours were fitted to the recorded spectra to determine the electric-quadrupole admixture in forbidden lines. The E2 admixtures found are: (3.49 ± 0.35)% and (37.1 ± 1.8)% for 459.7 and 564.0 nm lines, respectively. Our results are compared with recent theories and other experiments.
Critical examination of isotope shift and fine structure measurements for optical transitions in 6,7LiThis paper was presented at the International Conference on Precision Physics of Simple Atomic Systems, held at University of Windsor, Windsor, Ontario, Canada on 21–26 July 2008.
Authors: Noble George A. , van Wijngaarden William A. 
Published: April 2011

Precise isotope shift and fine structure measurements are critically reviewed. Each experiment was checked for whether the data found for different transitions yielded consistent values for the difference in mean-square nuclear charge radius Δr2 of 6,7Li. Experiments that passed this test found Δr2 = 0.735 ± 0.036, 0.755 ± 0.023, and 0.739 ± 0.013 fm2 by studying the Li+ 1s2s 3S→1s2p 3P transition, the Li D lines and the Li 2S1/2→3S1/2 transition, respectively. These data determine the difference in mean-square nuclear charge radius 25 times more accurately than electron scattering. Similarly, averaging the fine structure data from the same experiments gives 62 678.75 ± 0.55 MHz for the 7Li+ 1s2p 3P1–2 interval, in good agreement with theory. The results for the 6,7Li 2P fine structure intervals, 10 0.52.954 ± 0.049 and 10 053.154 ± 0.040 MHz, exceed computed values by 2 MHz and yield a splitting isotope shift, which is nearly a factor of 2 lower than a theoretical estimate.
Features of relativistic charged particles produced in catastrophic destruction of heavy emulsion nuclei at 4.5 A GeV
Authors: Singh P , Khan M S , Khushnood H 
Published: April 2011

Total disintegration events produced in 4.5 A GeV/c 12C--AgBr reactions are analysed to investigate the characteristics of secondary charged particles produced in such collisions. The results reveal that multiplicity distributions of grey, black, and relativistic charged particles agree with the Poisson distribution. The average multiplicity of grey particles is found to increase with the increasing mass of projectile, while the average value of black particles is found to decrease with the increasing mass of projectile. This result is in good agreement with the prediction of fireball model. Finally, the linear dependence of grey and compound multiplicities on black, heavy, and relativistic charged particles is also observed. PACS No.: 25.70
Effect of rainfall on matric suctions in a residual soil slope
Authors: Lim T T , Rahardjo H , Chang M F , Fredlund D G 
Published: April 2011

A slope stability study involving shallow slip surfaces should include the effect of negative pore-water pressures in a slope. A field instrumentation program was carried out to monitor negative pore-water pressure (i.e., in situ matric suction) in a residual soil slope in Singapore. Variations in matric suction and the matric suction profiles under (1) a canvas-convered grassed surface, (2) a grassed surface, and (3) a bare ground surface, in response to rainfalls were investigated. Changes in matric suction due to changes in climatic conditions decrease rapidly with depth. The change was found to be most significant in the bare slope and least significant under the canvas-covered slope. The amount of decrease in matric suction after a rainstorm was observed to be a function of the initial matric suction just prior to the rainstorm. Positive pore-water pressures were observed above the groundwater table, suggesting the development of a perched water table within the slope. These observations are also typical of other regions experiencing high seasonal rainfalls. The field monitoring program presented can be adopted for investigating rainfall-induced landslides in other parts of the world. Key words: matric suction, negative pore-water pressure, field instrumentation, rainfall, residual soil, slope stability.
Isolation and characterization of ACC deaminase genes from two different plant growth-promoting rhizobacteria
Authors: Shah Salehuzzaman , Li Jiping , Moffatt Barbara A , Glick Bernard R 
Published: April 2011

We have recently proposed that one way that plant growth-promoting rhizobacteria (PGPR) stimulate plant growth is through the activity of the enzyme 1-aminocyclopropane-1-carboxylate (ACC) deaminase, which causes a lowering of plant ethylene levels resulting in longer roots. As part of an effort to understand the role of this enzyme in PGPR, the genes for ACC deaminase from two PGPR, Enterobacter cloacae CAL2 and UW4, have been isolated. These genes are highly homologous to the ACC deaminase genes from Pseudomonas strains 6G5 and F17 and similar to the ACC deaminase gene from Pseudomonas sp. strain ACP. The region downstream (i.e., at the 3'-terminal end) of the strain UW4 ACC deaminase gene has a potential hairpin-like transcription termination site. The regions upstream of the strains UW4 and CAL2 ACC deaminase genes contain putative ribosome-binding sites; however, the promoter sequences have not yet been identified. Southern hybridization experiments suggest that there is a single copy of the ACC deaminase gene in Enterobacter cloacae strains UW4 and CAL2 and that there may be several different types of ACC deaminase genes in different microbes. The cloned ACC deaminase gene can be expressed in Escherichia coli enabling this bacterium to grow on ACC as a sole source of nitrogen and confers upon both Escherichia coli and Pseudomonas spp. strains that are transformed with this gene the ability to promote the elongation of the roots of canola seedlings.Key words: plant growth-promoting rhizobacteria, PGPR, 1-aminocyclopropane-1-carboxylate, ACC, ACC deaminase, ethylene, soil bacteria.
Increased nitric oxide production in platelets from severe chronic renal failure patients
Authors: Alves de Sá Siqueira Mariana , Brunini Tatiana M.C. , Rodrigues Pereira Natália , Martins Marcela Anjos , Bandeira Moss Monique , Santos Sérgio F. , Lugon Jocemir R. , Mendes-Ribeiro Antônio C. 
Published: April 2011

Nitric oxide (NO) production occurs through oxidation of the amino acid l-arginine by NO synthase (NOS). NO inhibits platelet activation by increasing the levels of cyclic guanosine monophosphate (cGMP), thus maintaining vascular homeostasis. Our group previously demonstrated ( da Silva et al. 2005 ) an enhancement of the l-arginine–NO–cGMP pathway in platelets taken from chronic renal failure (CRF) patients on haemodialysis associated with reduced platelet aggregation. We investigate the platelet l-arginine–NO–cGMP pathway, platelet function, and inflammation from patients in CRF on conservative treatment. A total of 42 CRF patients and 42 controls (creatinine clearance = 27 ± 3 vs. 93 ± 1 mL per min per 1.73 m2, respectively) participated in this study. NOS activity and expression and cGMP concentration were measured in platelets. Platelet aggregation induced by collagen or ADP was evaluated and plasma levels of fibrinogen were determined by the Clauss method. A marked increase in basal NOS activity was seen in undialysed CRF patients compared with controls, accompanied by an elevation of fibrinogen plasma levels. There were no differences in expression of NOS and in cGMP levels. In this context, platelet aggregation was not affected. We provide the first evidence of increased intraplatelet NO biosynthesis in undialysed CRF patients, which can be an early marker of future haemostatic abnormalities during dialysis treatment.
Fenofibrate lowers blood pressure in two genetic models of hypertension
Authors: Shatara Raied Khaled , Quest Dale W , Wilson Thomas W 
Published: April 2011

Fenofibrate, a commonly used lipid lowering drug, induces the expression of the gene coding for cytochrome P450-4A, whose major product is 20-hydroxyeicosatetraenoic acid (20-HETE). 20-HETE, a potassium channel antagonist, could increase or decrease blood pressure (BP). We studied the effects of four weeks of oral fenofibrate on BP, urine output (UVol), plasma renin activity (PRA), and urine protein excretion in young (4-5 weeks) stroke prone spontaneously hypertensive rats (SHRSP), older (25 weeks) SHRSP, Dahl salt sensitive rats (Dahl S) on a high salt diet, Dahl S rats on a normal salt diet, and normotensive Sprague-Dawley (SD) rats. Fenofibrate prevented the increase in BP in 4-5 week old SHRSP, reduced BP in 25 week old SHRSP, but had no effect on BP in normotensive SD rats. Similarly, fenofibrate prevented the increase in BP in Dahl S rats on a high salt diet, but had no effect in Dahl S rats on a low salt diet. Fenofibrate increased UVol (and reduced weight gain) in young SHRSP and tended to increase it in other groups. It also increased PRA 2 to 5-fold in all groups except older SHRSP. Young SHRSP receiving fenofibrate excreted significantly less urine protein than control rats. The drug reduced proteinuria in Dahl S rats on high salt diet, but had no significant effect on proteinuria in other groups. In summary, fenofibrate reduced blood pressure and weight gain, increased UVol and PRA, and reduced urine protein excretion in young SHRSP. Other groups of animals showed these changes to a variable, but directionally similar extent. These findings are consistent with a natriuretic effect of fenofibrate.Key words: hypertension, animal models, natriuresis, fenfibrate, lipid lowering agents.
Endovascular Treatment of Tandem Extracranial/Intracranial Anterior Circulation Occlusions
Authors: Malik Amer M. , Vora Nirav A. , Lin Ridwan , Zaidi Syed F. , Aleu Aitziber , Jankowitz Brian T. , Jumaa Mouhammad A. , Reddy Vivek K. , Hammer Maxim D. , Wechsler Lawrence R. , Horowitz Michael B. , Jovin Tudor G. 
Published: April 2011

Background and Purpose—
Acute ischemic stroke due to tandem occlusions of the extracranial internal carotid artery and intracranial arteries has a poor natural history. We aimed to evaluate our single-center experience with endovascular treatment of this unique stroke population.

Methods—
Consecutive patients with tandem occlusions of the internal carotid artery origin and an intracranial artery (ie, internal carotid artery terminus, M1 middle cerebral artery, or M2 middle cerebral artery) were studied retrospectively. Treatment consisted of proximal revascularization with angioplasty and stenting followed by intracranial intervention. Endpoints were recanalization of both extracranial and intracranial vessels (Thrombolysis In Myocardial Ischemia ≥2), parenchymal hematoma, and good clinical outcome (modified Rankin Scale ≤2) at 3 months.

Results—
We identified 77 patients with tandem occlusions. Recanalization occurred in 58 cases (75.3%) and parenchymal hematoma occurred in 8 cases (10.4%). Distal embolization occurred in 3 cases (3.9%). In 18 of 77 patients (23.4%), distal (ie, intracranial) recanalization was observed after proximal recanalization, obviating the need for distal intervention. Good clinical outcomes were achieved in 32 patients (41.6%). In multivariate analysis, Thrombolysis In Myocardial Ischemia ≥2 recanalization, baseline National Institutes of Health Stroke Scale score, baseline Alberta Stroke Programme Early CT score, and age were significantly associated with good outcome.

Conclusions—
Endovascular therapy of tandem occlusions using extracranial internal carotid artery revascularization as the first step is technically feasible, has a high recanalization rate, and results in an acceptable rate of good clinical outcome. Future randomized, prospective studies should clarify the role of this approach.