Quantum critical scaling at a Bose-glass/superfluid transition: Theory and experiment for a model quantum magnet

In this paper we investigate the quantum phase transition from magnetic Bose Glass to magnetic Bose-Einstein condensation induced by amagnetic field in NiCl2 center dot 4SC(NH2)(2) (dichloro-tetrakis-thiourea-nickel, or DTN), doped with Br (Br-DTN) or site diluted. Quantum Monte Carlo simulations for the quantum phase transition of the model Hamiltonian for Br-DTN, as well as for site-diluted DTN, are consistent with conventional scaling at the quantum critical point and with a critical exponent z verifying the prediction z = d; moreover the correlation length exponent is found to be nu = 0.75(10), and the order parameter exponent to be beta = 0.95(10). We investigate the low-temperature thermodynamics at the quantum critical field of Br-DTN both numerically and experimentally, and extract the power-law behavior of the magnetization and of the specific heat. Our results for the exponents of the power laws, as well as previous results for the scaling of the critical temperature to magnetic ordering with the applied field, are incompatible with the conventional crossover-scaling Ansatz proposed by Fisher et al. [Phys. Rev. B 40, 546 (1989)]. However they can all be reconciled within a phenomenological Ansatz in the presence of a dangerously irrelevant operator.

Low-temperature thermodynamic properties near the field-induced quantum critical point in NiCl2-4SC(NH2)(2)

We present a comprehensive experimental and theoretical investigation of the thermodynamic properties: specific heat, magnetization, and thermal expansion in the vicinity of the field-induced quantum critical point (QCP) around the lower critical field H-c1 approximate to 2 T in NiCl2-4SC(NH2)(2). A T-3/2 behavior in the specific heat and magnetization is observed at very low temperatures at H = H-c1, which is consistent with the universality class of Bose-Einstein condensation of magnons. The temperature dependence of the thermal expansion coefficient at H-c1 shows minor deviations from the expected T-1/2 behavior. Our experimental study is complemented by analytical calculations and quantum Monte Carlo simulations, which reproduce nicely the measured quantities. We analyze the thermal and the magnetic Gruneisen parameters, which are ideal quantities to identify QCPs. Both parameters diverge at H-c1 with the expected T-1 power law. By using the Ehrenfest relations at the second-order phase transition, we are able to estimate the pressure dependencies of the characteristic temperature and field scales.

Bose glass and Mott glass of quasiparticles in a doped quantum magnet

The low-temperature states of bosonic fluids exhibit fundamental quantum effects at the macroscopic scale: the best-known examples are Bose-Einstein condensation and superfluidity, which have been tested experimentally in a variety of different systems. When bosons interact, disorder can destroy condensation, leading to a 'Bose glass'. This phase has been very elusive in experiments owing to the absence of any broken symmetry and to the simultaneous absence of a finite energy gap in the spectrum. Here we report the observation of a Bose glass of field-induced magnetic quasiparticles in a doped quantum magnet (bromine-doped dichloro-tetrakis-thiourea-nickel, DTN). The physics of DTN in a magnetic field is equivalent to that of a lattice gas of bosons in the grand canonical ensemble; bromine doping introduces disorder into the hopping and interaction strength of the bosons, leading to their localization into a Bose glass down to zero field, where it becomes an incompressible Mott glass. The transition from the Bose glass (corresponding to a gapless spin liquid) to the Bose-Einstein condensate (corresponding to a magnetically ordered phase) is marked by a universal exponent that governs the scaling of the critical temperature with the applied field, in excellent agreement with theoretical predictions. Our study represents a quantitative experimental account of the universal features of disordered bosons in the grand canonical ensemble.

Terapia pulpar em dentes decíduos: possibilidades terapêuticas baseadas em evidências

Introduction: Pulpotomy of primary teeth has been the treatment of choice in cases of inflammation of the coronal pulp caused by caries or trauma with no involvement of the radicular pulp, thus avoiding the premature loss of the teeth. Not only is the diagnosis of the inflamed dental pulp required for this therapy to succeed, but also the selection of an effective and biocompatible medicament. However, none of the drugs available and recommended for pulpotomy therapy present all the requirements of an ideal pulp capping agent. Objective: Through a systematic literature review, between the years of 2000 and 2011, focusing in randomized clinical trials, systematic reviews and meta-analysis, aiming to analyze and discuss based on alternatives for the treatment of pulpotomy in human deciduous teeth. Conclusion: Scientific evidences showed that the medicaments and techniques influence were few. Thus, further and well-designed studies are suggested for clarification. The information generated in such experiments may contribute to a better understanding of the mechanisms of pulp therapy to new therapeutic approaches aimed at improving pulp therapy in deciduous teeth.

Clinical, radiographic and histologic analysis of the effects of pulp capping materials used in pulpotomies of human primary teeth

Aim: To compare the clinical, radiographic and histological responses of the pulp to mineral trioxide aggregate (MTA), calcium hydroxide (CH) and Portland cement (PC) when used as a pulpotomy agent in human primary teeth. Study design: Forty-five mandibular primary molar teeth were randomly assigned to CH, MTA or PC groups and treated by pulpotomy technique. Methods: The teeth were treated by conventional pulpotomy technique, differing only in the capping material for each group. Clinical and radiographic evaluations were recorded at 6-, 12- and 24-month follow-up. Teeth in the regular exfoliation period were further processed for histologic analysis. Statistics: The teeth were treated by conventional pulpotomy technique, differing only in the capping material for each group. Clinical and radiographic evaluations were recorded at 6-, 12- and 24-month follow-up. Teeth in the regular exfoliation period were further processed for histologic analysis. Statistics: Clinically and radiographically, the MTA and PC groups showed 100 % success rates at 6, 12 and 24 months. In CH group, several teeth presented clinical and radiographic failures detected throughout the follow-up period, and internal resorption was a frequent radiographic finding. Histologic analysis revealed the presence of dentine-like mineralised material deposition obliterating the root canal in the PC and MTA groups. CH group presented, in most of the sections, necrotic areas in the root canals. Conclusions: MTA and PC may serve as effective materials for pulpotomies of primary teeth as compared to CH. Although our results are very encouraging, further studies and longer follow-up assessments are needed in order to determine the safe clinical indication of Portland cement.

Oral antibacterial effect of chlorhexidine treatments and professional prophylaxis in children

Aim: The primary aim of this longitudinal study was to evaluate additional effects of 4-week chlorhexidine digluconate (CHX) gel treatments to control Aggregatibacter actinomycetemcomitans counts in children after professional dental prophylaxis. Porphyromonas gingivalis and Streptococcus mutans counts were also determined to evaluate the secondary effects of anti-plaque treatments on microbial shifts. Methods: Twenty-six children with A. actinomycetemcomitans counts >4 log10/ mL of saliva and/or Quigley-Hein plaque index >3.0 were enrolled in this study. Patients were randomly assigned to groups GI (placebo gel), GII (0.5% CHX gel), GIII (1% CHX gel), and GIV (2% CHX gel). Four sessions of treatment were performed during 4 weeks after a session of professional dental prophylaxis. Real-Time polymerase chain reaction (PCR) was used to determine viable microorganism counts in non-stimulated whole saliva samples collected at baseline, one week, one month and three months after interruption of treatments. Results: A reduction of all bacterial counts was detected after the 3-month follow-up in all groups. Lower counts of P. gingivalis were achieved from 1 week on after treatments. The 2% CHX concentration seemed to contribute to lower A. actinomycetemcomitans levels and increase S. mutans levels. Conclusions: Professional dental prophylaxis was effective to control salivary levels of A. actinomycetemcomitans, P. gingivalis and S. mutans. Additional antimicrobial effects, however, were not observed by the combination of professional dental prophylaxis and 4-week chlorhexidine gel treatments.