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Non-Gaussian random-matrix ensembles with banded spectra.

Non-Gaussian random-matrix ensembles are important in many applications. We propose Monte Carlo and Langevin methods for generating non-Gaussian ensembles and their eigenvalue spectra. We also provide a general framework for analytic studies of the level density in these ensembles. We show that, in general, the level densities exhibit banded spectra, with important implications for mesoscopic systems and complex nuclei. The universality of energy-level fluctuations is confirmed.

Journal Article↗

Crystal-matrix interrelations in brushite and uric acid calculi.

Brushite and uric acid calculi were studied by means of scanning electron microscopy with the partial dissolution method and transmission electron microscopy. Brushite calculi consist of radially oriented columnar crystals which have sheet-like substructure. The organic matrix is identified chiefly at the outside of the crystals but partly included between the substructure. The concentric matrix bands are often dislocated between the neighbouring crystals. Uric acid calculi also consist of radially oriented columnar crystals, and a fine meshwork of the organic matrix is incorporated within the crystals. The concentric matrix layers of different density are angled according to the crystal lattice. These findings indicate that the organic matrix arose from a mucinous surface coat, at least in the radially striated calculi. The crystals continued to grow in this gel-state milieu, either thrusting the matrix aside or incorporating it within the crystals.

Calcium Oxalate↗

Bone chemical structure response to mechanical stress studied by high pressure Raman spectroscopy.

While the biomechanical properties of bone are reasonably well understood at many levels of structural hierarchy, surprisingly little is known about the response of bone to loading at the ultrastructural and crystal lattice levels. In this study, our aim was to examine the response (i.e., rate of change of the vibrational frequency of mineral and matrix bands as a function of applied pressure) of murine cortical bone subjected to hydrostatic compression. We determined the relative response during loading and unloading of mineral vs. matrix, and within the mineral, phosphate vs. carbonate, as well as proteinated vs. deproteinated bone. For all mineral species, shifts to higher wave numbers were observed as pressure increased. However, the change in vibrational frequency with pressure for the more rigid carbonate was less than for phosphate, and caused primarily by movement of ions within the unit cell. Deformation of phosphate on the other hand, results from both ionic movement as well as distortion. Changes in vibrational frequencies of organic species with pressure are greater than for mineral species, and are consistent with changes in protein secondary structures such as alterations in interfibril cross-links and helix pitch. Changes in vibrational frequency with pressure are similar between loading and unloading, implying reversibility, as a result of the inability to permanently move water out of the lattice. The use of high pressure Raman microspectroscopy enables a deeper understanding of the response of tissue to mechanical stress and demonstrates that individual mineral and matrix constituents respond differently to pressure.

Animals↗

Comparison of basement membrane matrix degradation by purified proteases and by metastatic tumor cells.

We have examined the nature of biochemical degradation of an isolated basement membrane matrix (bovine lens capsule) using different methodologies. The first strategy was quantitation of the release of surface-bound 125I and a second the documentation by SDS-PAGE of the appearance of putative cleavage products and the loss of high-molecular-weight components from the matrix. Basement membrane matrix bands resolved on SDS-PAGE were identified by their protease sensitivities as well as by Western immunoblots using monoclonal antibodies developed for this study. Radioiodinated components were found predominantly at positions on the gel equivalent to 160-200 kd and 400 kd proteins. Since these labeled moieties were sensitive to bacterial collagenase digestion and stained with anticollagen type IV antibodies, they were determined to represent various configurations of collagen type IV. Several other lower-molecular-weight bands also stained with the anticollagen IV antibodies. Monoclonal antibodies reactive with laminin exhibited a complex staining pattern on the gels, which included the expected 200 and 400 kd components. We confirmed that lens capsule basement membrane contained only a single heparan sulfate glycosaminoglycan species, and tumor cell-induced glycosaminoglycan degradation within the basement membrane matrix was detected using cellulose acetate electrophoresis. Distinctive putative cleavage products were resolved on SDS-PAGE gels from matrices subjected to digestion by a variety of purified proteases as well as by metastatic tumor cells or their conditioned media. Tumor cells of different histiotypes produced different characteristic cleavage patterns, suggestive of the existence of several pathways of matrix degradation. Overall, primary tumor cells exhibited a greater degradative activity towards the basement membrane matrix than did long-term tissue culture-passaged cells. The same tumor cell line could exhibit considerably different patterns of both protein and glycosaminoglycan degradation depending on recent culture history. The relevance of these biochemical studies to the pathogenesis of malignant neoplasms is shown by: 1) the evaluation of degradative activities of B16 tumor cell populations exhibiting enhanced lung-colonizing phenotypes, and 2) the ability of a known antimetastatic moiety with antiprotease activity (Haementeria leech species salivary gland extract) to protect matrix components from degradation by tumor cell-conditioned medium.

Animals↗

Surface hardness of light-cured composite resin cured directly or through a transparent matrix using three different light guides.

The purpose of this study was to compare the Vickers Hardness (HV) of composite resin which was light-cured by 3 different light guides, either through or without a transparent polyester matrix band. The 3 light guides, standard Demetron (SG), Turbo Tip (TT) and a standard Demetron, with obvious accidental damage (DL) were tested with both Model 100 and Cure Rite radiometers. HV tests were done on all samples both immediately and one hour after light-curing. Results were analysed using the Anova and Student t-test. The light intensity readings in mW/cm2 were SG 600 and TT 850 with both radiometers and DL tested 350 and 380. Composite resin surfaces undergo significant surface hardening in the first hour after light-curing. A 350-380 mW/cm2 intensity gives significantly lower HV than 600 + mW/cm2 but 800 mW/cm2 does not produce significantly greater HV than 600 mW/cm2. Curing through a transparent polyester matrix gives marginally greater HV than curing directly. The output of light guides is a significant factor in the surface hardness of cured composite resin.

Analysis of Variance↗

Iatrogenic damage to the adjacent surfaces of primary molars, in three different ways of cavity preparation.

AIM: A clinical study was carried out to compare three methods of preparing a cavity regarding the measure of damage to adjacent teeth: the ART method, the use of the latest version of Carisolv and as a control group the use of rotating instruments. METHODS: Preparations (217) were made by 2 Tanzanian dentists and 2 final year Dutch dental students at the Muhimbili University College of Health Science (MUCHS) in Dar es Salaam, Tanzania. Only children 7 years old, with one class II cavity in a primary molar and no dental experience were included in the study. After cavity preparation, partial impressions of the adjacent teeth were made, from which resin models were cast and later studied under a stereomicroscope. RESULTS: These showed damage of 91.7% in the Bur group, which was significantly greater than in the ART and Carisolv groups (62.7% and 59.5% respectively). CONCLUSION: Protection of the adjacent surfaces is necessary, for instance in the form of matrix band separation and by means of damage reducing techniques. More studies on the long term effect of the damage need to be conducted.

Child↗

Dental bacteremia in children.

Bacteremia resulting from dental extraction is regarded as an important cause of bacterial endocarditis, and it is therefore recommended that patients undergoing tooth extraction be given prophylactic antibiotics. As dental procedures other than extractions may also cause bacteremias, we studied a variety of dental procedures routinely used in pediatric dentistry. Blood samples for cultures were obtained 30 s after each of 13 dental operative procedures in 735 anesthetized children aged 2-16 years. Four procedures used for conservative dentistry caused bacteremias significantly more often than the baseline value of 9.4%: polishing teeth 24.5%, intraligamental injection 96.6%, rubber dam placement 29.4%, and matrix band with wedge placement 32.1%. In comparison, toothbrushing alone caused a bacteremia on 38.5% of occasions. The organisms isolated were typical of odontogenic bacteremias in that 50% of the isolates were identified as varieties of viridans streptococci. These data show that a wider variety of dental procedures than was previously documented cause bacteremia.

Adolescent↗

A technique for fabricating dies.

A technique for fabricating dies without using a die saw has been described. The technique saves the time consumed in sawing the dies and eliminates the hazards of using a die saw. It is particularly advantageous when little space exists between dies since the Zolnowski matrix band is thinner than the thinnest saw blade. The band can be easily placed in the tightest interproximal spaces and can be secured in place with a minimum amount of sticky wax. The technique can be used for crowns, fixed partial dentures, and indirect inlays.

Dental Casting Technique↗

Reinforced matrices for pin-amalgam restorations reduce microleakage.

The considerable decrease in microkeakage in the compound-reinforced restorations may be due to the tighter fit of the matrix band at the gingival wall of the preparation, which allows better condensation and marginal sealing of the restoration. The compound prevents lateral migration of the band during condensation pressures.

Dental Amalgam↗

Handling characteristics of gallium alloy for dental restoration.

The handling characteristics of a gallium alloy (Gallium Alloy GF) were compared to those of a spherical high-copper amalgam (Tytin). Ten dentists each restored four identical MO preparations in acrylic typodont teeth (no. 30), two with amalgam and two with gallium alloy. Each restoration was evaluated immediately following completion by the operator for six clinically relevant criteria. Each criterion was scored between 1 and 5, where 1 = very poor, 2 = poor, 3 = fair, 4 = good, and 5 = very good. Three two-sided Mann-Whitney tests were used to compare the median scores for significant differences (P < 0.05). The first test indicated no significant difference between scores for the first- and second-placed restorations, within criteria and within alloy type (n = 10). The second test indicated a significant difference between amalgam and gallium alloy, within criteria and within restoration sequence (n = 10), for each criterion except resistance to fracture during removal of the matrix band. The third test indicated a significant difference between amalgam and gallium alloy, within each criteria, combining scores for first- and second-placed restorations (n = 20). During simulated clinical placement, amalgam was rated significantly higher than gallium alloy in each handling characteristic evaluated.

Dental Alloys↗

Atraumatic restorative techniques could reduce discomfort in children receiving dental treatment.

DESIGN: This was a randomised controlled trial conducted in Indonesia. INTERVENTION: Children, who each had at least one multisurface cavity in a deciduous molar, were randomly allocated to two treatment groups. The test group was treated using atraumatic restorative techniques (ART) using only hand instruments. The control group received treatment using rotary instruments (operated at 750 rpm), without water cooling. Glass ionomer cement was used for restoration in both groups. OUTCOME MEASURE: The extent of discomfort was assessed by measuring the behavioural (psychological) and the physiological aspect represented by, respectively, a modified Venham score and the heart rate of the children at six fixed moments during dental treatment: (i) when the child entered the treatment room, (ii) at the start of excavation, (iii) at the moment of deepest excavation, (iv) at the moment of application of the matrix band and wedges, (v) at the moment the restoration was applied, and (vi) after completion of the treatment. RESULTS: A total of 403 children were treated. Venham scores showed a marked difference between the two groups at most timepoints. Heart rate measurements were different at deep excavation. Also, a clear relation between Venham scores and heart rate measurements could be found at all time points. Confounding could be shown for operating dentist, gender of the patient and initial anxiety, but not for age. No effect modification could be shown. CONCLUSIONS: Children treated according to the ART approach using hand instruments alone experience less discomfort than those treated using rotary instruments.

Comment↗

Spectral difference Lanczos method for efficient time propagation in quantum control theory.

Spectral difference methods represent the real-space Hamiltonian of a quantum system as a banded matrix which possesses the accuracy of the discrete variable representation (DVR) and the efficiency of finite differences. When applied to time-dependent quantum mechanics, spectral differences enhance the efficiency of propagation methods for evolving the Schrodinger equation. We develop a spectral difference Lanczos method which is computationally more economical than the sinc-DVR Lanczos method, the split-operator technique, and even the fast-Fourier-Transform Lanczos method. Application of fast propagation is made to quantum control theory where chirped laser pulses are designed to dissociate both diatomic and polyatomic molecules. The specificity of the chirped laser fields is also tested as a possible method for molecular identification and discrimination.

Journal Article↗

Numerical study of eigenvector statistics for random banded matrices.

The statistics of eigenvector amplitudes near the band center in random-banded-matrix ensembles is studied numerically. The nonlinear sigma model provides a rigorous description of the statistics in these ensembles. We are interested in the extension of the predictions of the sigma model approach to complex quantum systems. We study the validity range of the perturbation theory beginning from the well-known formulas in random matrix theory.

Journal Article↗

Fluctuations of the inverse participation ratio at the anderson transition

Statistics of the inverse participation ratio (IPR) at the critical point of the localization transition is studied numerically for the power-law random banded matrix model. It is shown that the IPR distribution function is scale invariant, with a power-law asymptotic "tail." This scale invariance implies that the fractal dimensions D(q) are nonfluctuating quantities, contrary to a recent claim in the literature. A recently proposed relation between D2 and the spectral compressibility chi is violated in the regime of strong multifractality, with chi-->1 in the limit D2-->0.

Journal Article↗

Fluctuations of the correlation dimension at metal-insulator transitions.

We investigate numerically the inverse participation ratio, P(2), of the 3D Anderson model and of the power-law random banded matrix (PRBM) model at criticality. We found that the variance of lnP(2) scales with system size L as sigma(2)(L) = sigma(2)(infinity)-AL(-D(2)/2d), with D(2) being the correlation dimension and d the system dimension. Therefore the concept of a correlation dimension is well defined in the two models considered. The 3D Anderson transition and the PRBM transition for b = 0.3 (see the text for the definition of b) are fairly similar with respect to all critical magnitudes studied.

Journal Article↗

QCD vacuum as a disordered medium: a simplified model for the QCD dirac operator.

We model the QCD Dirac operator as a power-law random banded matrix (RBM) with the appropriate chiral symmetry. Our motivation is the form of the Dirac operator in a basis of instantonic zero modes with a corresponding gauge background of instantons. We compare the spectral correlations of this model to those of an instanton liquid model (ILM) and find agreement well beyond the Thouless energy. In the bulk of the spectrum the dimensionless Thouless energy of the RBM scales with the square root of system size in agreement with the ILM and chiral perturbation theory. Near the origin the scaling in the RBM remains the same as in the bulk which agrees with chiral perturbation theory but not with the ILM. Finally we discuss how this RBM should be modified in order to describe the spectral correlations of the QCD Dirac operator at the finite temperature chiral restoration transition.

Journal Article↗

CJD: update for dental staff.

UNLABELLED: It is almost a decade since the recognition of the emergence of a new infectious disease termed variant Creutzfeldt-Jakob disease (vCJD) caused by prions (PrPTSE), abnormal variants of a normal human cell surface protein (PrP). This disease has a number of similarities to other forms of CJD--lethal disorders characterized by a prolonged incubation period, and progressive mental deterioration. In relation to oral tissues, PrPTSE have been found in neural, gingival, pulpal, lingual, lymphoreticular and salivary gland tissue in animal models. In both sporadic and variant CJD, PrPTSE is detectable in the trigeminal ganglion and, in vCJD, in lymphoreticular tissues, but infectivity has not been tested in other human oral tissues. CLINICAL RELEVANCE: PrPTSE is much more resistant to the common methods of inactivation than conventional pathogens, and it adheres avidly to steel whilst retaining its infectivity. Particular attention must be paid to cleaning and sterilizing re-usable dental instruments. Single-use devices, such as endodontic files and matrix bands, must never be re-used. Advice on the reprocessing of dental instruments used on known CJD patients must be obtained from local infection control teams. Research into effective methods of prion inactivation appears promising, although further work on the applicability to general dental practice is required.

Animals↗

Grating diffraction and Wood's anomalies at two-dimensionally periodic impedance surfaces.

We address the problem of plane-wave scattering and Wood's anomalies at two-dimensional (2-D) periodic surfaces by employing a simplified grating model given by a planar surface whose impedance varies sinusoidally along two orthogonal directions. We obtain a rigorous solution to the corresponding boundary-value problem in terms of an infinite set of coupled recurrence equations. When truncated for computational purposes, this solution is in the form of a banded matrix, which we solve by direct methods and also by a highly efficient iterated matrix procedure. Numerical results are presented for symmetric and nonsymmetric incidence cases, and we show that certain diffracted fields do not depolarize in the former case. The expected Wood's anomalies of both Rayleigh and leaky-wave types are confirmed, and their location in wavelength space is numerically demonstrated for 2-D periodic configurations.

Journal Article↗