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PubMed2005

The difficulty in the assessment of the compression behaviour of powder mixtures: Double layer tablets versus arithmetic additivity rule.

The weighted arithmetic mean from values of a feature derived from the individual components is often used to calculate the theoretically expected compression behaviour of powder mixtures if no interparticulate interactions between the components occur. Alternatively, simulated and experimental double layer tablets are presented. The suitability of the various methods to serve as a reference for the assessment of the compression behaviour of powder mixtures shall be compared. Narrow and similar sieve fractions of maltitol and metamizol were mixed in various ratios of true volumes. Constant total true volumes of the single substances, powder mixtures, and layered powders of the same composition were compressed on an eccentric tabletting machine to a constant maximum geometric mean punch force. In addition, the compression of double layer tablets was mathematically simulated from the dynamic relative density-force data of the pure materials. At a given momentary force, the relative density of a simulated double layered powder bed is given by the harmonic mean of the relative density values of the pure materials weighted by their true volume fractions. The results show that the total, the net, and the expansion work change indeed almost linearly with the true volume fraction of the components in the double layer tablets, with the consequence that the plasticity index (=net work/total workx100) proceeds non-linearly. The slope of the Heckel plot 'at pressure' and the apparent mean yield pressure obtained from these Heckel data are non-linearly related to the true volume fraction. If the weighted arithmetic mean is used to analyse the compression behaviour of the powder mixtures, results are obtained which are incompatible or even contradictory between interrelated features. On the other hand, the double layer model provides a consistent evaluation. A good agreement between the results of the experimental and the simulated double layer tablets is found.

Algorithms↗
PubMed2005

Effect of slow-acting wide dynamic range compression on measures of intelligibility and ratings of speech quality in simulated-loss listeners.

The purpose of this study was twofold: (a) to determine the extent to which 4-channel, slow-acting wide dynamic range amplitude compression (WDRC) can counteract the perceptual effects of reduced auditory dynamic range and (b) to examine the relation between objective measures of speech intelligibility and categorical ratings of speech quality for sentences processed with slow-acting WDRC. Multiband expansion was used to simulate the effects of elevated thresholds and loudness recruitment in normal hearing listeners. While some previous studies have shown that WDRC can improve both speech intelligibility and quality, others have found no benefit. The current experiment shows that moderate amounts of compression can provide a small but significant improvement in speech intelligibility, relative to linear amplification, for simulated-loss listeners with small dynamic ranges (i.e., flat, moderate hearing loss). This benefit was found for speech at conversational levels, both in quiet and in a background of babble. Simulated-loss listeners with large dynamic ranges (i.e., sloping, mild-to-moderate hearing loss) did not show any improvement. Comparison of speech intelligibility scores and subjective ratings of intelligibility showed that listeners with simulated hearing loss could accurately judge the overall intelligibility of speech. However, in all listeners, ratings of pleasantness decreased as the compression ratio increased. These findings suggest that subjective measures of speech quality should be used in conjunction with either objective or subjective measures of speech intelligibility to ensure that participant-selected hearing aid parameters optimize both comfort and intelligibility.

Acoustic Stimulation↗
PubMed2004

New view of the high-pressure behaviour of GdFeO(3)-type perovskites.

Recent determinations of the structures of several GdFeO(3)-type orthorhombic perovskites (ABO(3)) show that the octahedra in some become more tilted with increasing pressure. In others the octahedra become less tilted and the structure evolves towards a higher-symmetry configuration. This variety of behaviour can be explained in terms of the relative compressibilities of the octahedral and dodecahedral cation sites in the perovskite structure. If the BO(6) octahedra are less compressible than the AO(12) sites then the perovskite will become more distorted with pressure, but the perovskite will become less distorted if the BO(6) site is more compressible than the AO(12) site. In this contribution we use the bond-valence concept to develop a model that predicts the relative compressibilities of the cation sites in oxide perovskites. We introduce the site parameter M(i) defined in terms of the coordination number N(i), average bond length at room pressure R(i), and the bond-valence parameters R(0) and B,M(i) = ([R(i)N(i)/B)exp](R(0) - R(i))/B].M(i) represents the variation in the bond-valence sum at the central cation in a polyhedral site because of the change of the average bond distance. Experimental data suggest that the pressure-induced changes in the bond-valence sums at the two cation sites within any given perovskite are equal. With this condition we show that the ratio of cation-site compressibilities is given by betaB/beta(A) = M(A)/M(B). This model, based only upon room-pressure bond lengths and bond-valence parameters, correctly predicts the structural behaviour and some physical properties of the oxide perovskites that have been measured at high pressure.

Algorithms↗
PubMed2006

A three-state model for DNA protein-coding regions.

It is known that the protein-coding regions of DNA are usually characterized by a three-base periodicity. In this paper, we exploit this property, studying a DNA model based on three deterministic states, where each state implements a finite-context model. The experimental results obtained confirm the appropriateness of the proposed approach, showing compression gains in relation to the single finite-context model counterpart. Additionally, and potentially more interesting than the compression gain on its own, is the observation that the entropy associated to each of the three base positions of a codon differs and that this variation is not the same among the organisms analyzed.

Algorithms↗
PubMed1989

[Adjustment of hearing aids using a computer].

There was developed the programme for the fitting of hearing-aids for minicomputer SHARP PC 1500. According to the audiometric investigation the programme enables to choose the SPPL (Saturation Sound Pressure Level), gain, compression and frequency range. The programme was proved in the fitting of hearing-aids to thirty subjects, mostly with sensorineural hearing impairment. The use of the computer is considered as the simplifying of this work to the audiological personal.

Adolescent↗
PubMed1994

Intertrigo: a practical approach.

Although the precise diagnosis of intertriginous dermatosis is hampered by the unique conditions of the skin folds, there are a few common rules to be considered in the therapeutic approach. Dryness must be reached by changing occlusive conditions, astringent compresses, and absorbing powders. To improve the primary dermatosis, superimposed infection must be treated. With rare exceptions, fluorinated steroids should not be used in occlusive areas. Finally, the skills of a dermatologist may be required to optimize the care of patients with complex dermatoses involving the flexural skin.

Algorithms↗
PubMed1988

Auto-association by multilayer perceptrons and singular value decomposition.

The multilayer perceptron, when working in auto-association mode, is sometimes considered as an interesting candidate to perform data compression or dimensionality reduction of the feature space in information processing applications. The present paper shows that, for auto-association, the nonlinearities of the hidden units are useless and that the optimal parameter values can be derived directly by purely linear techniques relying on singular value decomposition and low rank matrix approximation, similar in spirit to the well-known Karhunen-Loève transform. This approach appears thus as an efficient alternative to the general error back-propagation algorithm commonly used for training multilayer perceptrons. Moreover, it also gives a clear interpretation of the rôle of the different parameters.

Mathematics↗
PubMed2006

Configurational constant pressure molecular dynamics.

We propose two new algorithms for generating isothermal-isobaric molecular dynamics. The algorithms are based on an extended phase space dynamics where two extra degrees of freedom, representing the thermostat and the barostat, are included. These new methods adopt a totally different approach towards molecular dynamics simulation in the isothermal-isobaric ensemble. They are fully configurational in the sense that only the particle positions are required in the control of the system temperature and pressure. Following on from the works of Delhommelle and Evans [Mol. Phys., 99, 1825 (2001)] and of Braga and Travis [J. Chem. Phys., 123, 134101 (2005)] concerning configurational canonical dynamics, these new algorithms can be seen as a natural extension to the isothermal-isobaric ensemble. We have validated both of our new configurational isothermal-isobaric schemes by conducting molecular dynamics simulations of a Lennard-Jones fluid and comparing the static and dynamic properties for a single state point. We find that both schemes generate similar results compared with schemes which use kinetic temperature and pressure control. We have also monitored the response of the system to a series of isothermal compressions and isobaric quenches. We find that the configurational schemes performed at least as well as the kinetic based scheme in bringing the system temperature and pressure into line with the set point values of these variables. These new methods will potentially play a significant role in simulations where the calculation of the kinetic temperature and pressure can be problematic. A well known example resides in the field of nonequilibrium simulations where the kinetic temperature and pressure require a knowledge of the streaming velocity of the fluid in order to calculate the true peculiar velocities (or momenta) that enter into their definitions. These are completely avoided by using our configurational thermostats and barostats, since these are independent of momenta. By extending the analysis of Kusnezov et al. [Ann. Phys., 204, 155 (1990)] in order to derive a set of generalized Nose-Hoover equations of motion which can generate isothermal-isobaric dynamics in a number of different ways, we are able to show that both of our new configurational barostats and Hoover's kinetic isothermal-isobaric scheme are special cases of this more general set of equations. This generalization can be very powerful in generating constant pressure dynamics for a variety of systems.

Journal Article↗
PubMedDate not supplied

Delayed union and nonunion following closed treatment of diaphyseal pediatric forearm fractures.

Delayed unions and nonunions of diaphyseal pediatric forearm fractures are exceedingly uncommon. In the past they generally have been reported in conjunction with open fracture or initial operative management of these fractures. The authors report six cases that occurred in low-energy, closed fractures initially managed with casting. The cases all occurred in teenage patients from age 13 to 16, and all cases involved the ulna. The mid-diaphysis was the most common location, and this may represent a watershed zone of perfusion with a relatively poor intraosseous blood supply. All of these patients were managed with compression plating with or without bone grafting. Three of these patients had rapid healing in an average of 2 months, while one had an inadequate radiographic record and another was lost to follow-up. The other patient had a more prolonged course to healing after surgery.

Adolescent↗
PubMed1984

Burst fractures of the thoracic and lumbar spine.

A burst fracture may be defined as an unstable compression fracture of the posterior wall of the vertebral body that allows fragments to be retropulsed into the spinal canal. Computerized axial tomography evaluation of these injuries often reveals posterior element fracture heretofore not stressed in the literature. In surgical treatment for these injuries four important considerations must be met; (1) the coronal and sagittal alignment of the spine; (2) patency of the neural canal; (3) the two-column concept of spinal stability; and (4) bony vertebral body reconstitution. An algorithm for treatment may be developed with the aid of these principles. Distraction and the creation of spinal lordosis are necessary for reduction.

Adult↗
PubMed1998

Compression of strings with approximate repeats.

We describe a model for strings of characters that is loosely based on the Lempel Ziv model with the addition that a repeated substring can be an approximate match to the original substring; this is close to the situation of DNA, for example. Typically there are many explanations for a given string under the model, some optimal and many suboptimal. Rather than commit to one optimal explanation, we sum the probabilities over all explanations under the model because this gives the probability of the data under the model. The model has a small number of parameters and these can be estimated from the given string by an expectation-maximization (EM) algorithm. Each iteration of the EM algorithm takes O(n2) time and a few iterations are typically sufficient. O(n2) complexity is impractical for strings of more than a few tens of thousands of characters and a faster approximation algorithm is also given. The model is further extended to include approximate reverse complementary repeats when analyzing DNA strings. Tests include the recovery of parameter estimates from known sources and applications to real DNA strings.

Algorithms↗
PubMed2004

Mass spectrometry of hydrogen/deuterium exchange of Escherichia coli dihydrofolate reductase: effects of loop mutations.

To address the effects of single amino acid substitutions on the structural fluctuation of Escherichia coli dihydrofolate reductase (DHFR), hydrogen/deuterium exchange kinetics were investigated at 15 degrees C with wild-type and mutant DHFRs at Gly67 (six mutants) and Gly121 (eight mutants) located in two flexible loops, by means of electrospray ionization mass spectrometry. These mutations induced significant changes in the first-order rate constant of proton exchange, k(ex) (0.10-0.27 min(-1)), the number of fast-exchangeable protons, Delta M(o) (164-222 Da), and the number of protons protected from exchange, Delta M(infinity) (15-56 Da), relative to the corresponding values for the wild-type enzyme (k(ex) = 0.18 min(-1), Delta M(o) = 164 Da, and Delta M(infinity) = 50.5 Da). These kinetic parameters were strongly correlated with the volume of introduced amino acids, but partly correlated with adiabatic compressibility (volume fluctuation), stability, and enzymatic activity. These results indicate that the local structure change due to a single amino acid substitution in loop regions is dramatically magnified to affect the structural fluctuation of the whole DHFR molecule, resulting in complicated changes in its stability and function.

Algorithms↗
PubMed2005

Fast generation of digitally reconstructed radiographs using attenuation fields with application to 2D-3D image registration.

Generation of digitally reconstructed radiographs (DRRs) is computationally expensive and is typically the rate-limiting step in the execution time of intensity-based two-dimensional to three-dimensional (2D-3D) registration algorithms. We address this computational issue by extending the technique of light field rendering from the computer graphics community. The extension of light fields, which we call attenuation fields (AFs), allows most of the DRR computation to be performed in a preprocessing step; after this precomputation step, DRRs can be generated substantially faster than with conventional ray casting. We derive expressions for the physical sizes of the two planes of an AF necessary to generate DRRs for a given X-ray camera geometry and all possible object motion within a specified range. Because an AF is a ray-based data structure, it is substantially more memory efficient than a huge table of precomputed DRRs because it eliminates the redundancy of replicated rays. Nonetheless, an AF can require substantial memory, which we address by compressing it using vector quantization. We compare DRRs generated using AFs (AF-DRRs) to those generated using ray casting (RC-DRRs) for a typical C-arm geometry and computed tomography images of several anatomic regions. They are quantitatively very similar: the median peak signal-to-noise ratio of AF-DRRs versus RC-DRRs is greater than 43 dB in all cases. We perform intensity-based 2D-3D registration using AF-DRRs and RC-DRRs and evaluate registration accuracy using gold-standard clinical spine image data from four patients. The registration accuracy and robustness of the two methods is virtually identical whereas the execution speed using AF-DRRs is an order of magnitude faster.

Algorithms↗
PubMedDate not supplied

A virtual reality patient simulation system for teaching emergency response skills to U.S. Navy medical providers.

Rapid and effective medical intervention in response to civil and military-related disasters is crucial for saving lives and limiting long-term disability. Inexperienced providers may suffer in performance when faced with limited supplies and the demands of stabilizing casualties not generally encountered in the comparatively resource-rich hospital setting. Head trauma and multiple injury cases are particularly complex to diagnose and treat, requiring the integration and processing of complex multimodal data. In this project, collaborators adapted and merged existing technologies to produce a flexible, modular patient simulation system with both three-dimensional virtual reality and two-dimensional flat screen user interfaces for teaching cognitive assessment and treatment skills. This experiential, problem-based training approach engages the user in a stress-filled, high fidelity world, providing multiple learning opportunities within a compressed period of time and without risk. The system simulates both the dynamic state of the patient and the results of user intervention, enabling trainees to watch the virtual patient deteriorate or stabilize as a result of their decision-making speed and accuracy. Systems can be deployed to the field enabling trainees to practice repeatedly until their skills are mastered and to maintain those skills once acquired. This paper describes the technologies and the process used to develop the trainers, the clinical algorithms, and the incorporation of teaching points. We also characterize aspects of the actual simulation exercise through the lens of the trainee.

Algorithms↗
PubMed2006

Pressure derivatives in the classical molecular-dynamics ensemble.

The calculation of thermodynamic state variables, particularly derivatives of the pressure with respect to density and temperature, in conventional molecular-dynamics simulations is considered in the frame of the comprehensive treatment of the molecular-dynamics ensemble by Lustig [J. Chem. Phys. 100, 3048 (1994)]. This paper improves the work of Lustig in two aspects. In the first place, a general expression for the basic phase-space functions in the molecular-dynamics ensemble is derived, which takes into account that a mechanical quantity G is, in addition to the number of particles, the volume, the energy, and the total momentum of the system, a constant of motion. G is related to the initial position of the center of mass of the system. Secondly, the correct general expression for volume derivatives of the potential energy is derived. This latter result solves a problem reported by Lustig [J. Chem. Phys. 109, 8816 (1998)] and Meier [Computer Simulation and Interpretation of the Transport Coefficients of the Lennard-Jones Model Fluid (Shaker, Aachen, 2002)] and enables the correct calculation of the isentropic and isothermal compressibilities, the speed of sound, and, in principle, all higher pressure derivatives. The derived equations are verified by calculations of several state variables and pressure derivatives up to second order by molecular-dynamics simulations with 256 particles at two state points of the Lennard-Jones fluid in the gas and liquid regions. It is also found that it is impossible for systems of this size to calculate third- and higher-order pressure derivatives due to the limited accuracy of the algorithm employed to integrate the equations of motion.

Journal Article↗
PubMed2004

Diagnostic classification of urothelial cells in urine cytology specimens using exclusively spectral information.

BACKGROUND: Although cytologic evaluation of urine specimens is a standard procedure in the diagnosis and follow-up of bladder carcinoma, its sensitivity and specificity are low. Cytopathologic diagnoses are driven primarily by spatial relations or morphology. Although color enhances the pathologist's perception of the specimen, spectral information plays a minimal role in diagnostic processes. Recently, methods have been developed to capture and analyze spectral information from clinical specimens. In the current study, the authors determined the classification value of spectral information by testing its ability to discriminate between malignant and benign urothelial cells in cytology specimens. METHODS: Multiple images of benign urothelial cells (n = 39) and urothelial carcinoma cells (n = 35) were collected at serial wavelengths using a liquid crystal tunable optical filter and composited into a mosaic using ENVI (Environment for Visualizing Images) software. Through minimum noise fractionation and principal component analysis, the spectral information in the mosaic was compressed into a 29-dimensional scatter plot. The data generated were analyzed using visual and spectral end member extraction on both the original data set and a second independent data set (test set). RESULTS: One area of spectral clustering in the scatter plot segmented with carcinoma cells exclusively (100% specific), but was not present in every cell (approximately 50%), which may indicate that these spectral profiles are present in a subpopulation of malignant cells or at specific points of their cell cycle. Using ENVI algorithms, the authors found that a particular classification spectrum (end member 9) and its closest relatives identified malignant cell clusters, with a sensitivity and specificity that reached 82% and 81%, respectively. To validate this mechanism in a test set, a second mosaic comprised of 15 benign and 15 malignant clusters was analyzed using end member 9, resulting in a combined sensitivity and specificity of 73%. CONCLUSIONS: The results of the current study demonstrate that spectral information, in the complete absence of morphologic or spatial information, allows discrimination of benign and malignant urothelial cells in routine urine cytology specimens. The authors believe that this novel technology, combined with spatial analysis, has the potential to serve as an ancillary test for improved detection of bladder carcinoma.

Cytodiagnosis↗
PubMed2005

Carotid compression: investigation of cerebral autoregulative reserve in rats.

Easy-to-perform, reversible techniques to analyse cerebral autoregulation are still missing in animal research. The carotid compression technique has been established to investigate dynamic cerebral autoregulation in humans. Adapting the carotid compression technique, we compared data from the new application with that of a classical exsanguination method. Compressing the ipsilateral carotid artery with a non-traumatic clip device for 10s modulated cerebral perfusion pressure. After clip release, the peaking laser-Doppler flow velocity increase over the somatosensory cortex allowed calculation of the transient hyperaemic response ratio (THRR) in relation to baseline. Modulating blood-pressure levels maintenance of cerebral blood-flow velocity was compared with THRR responses. With decreasing blood-pressure levels, the THRR first increased (29+/-16% at 95+/-10 mmHg to 39+/-13% at 75+/-10 mmHg) before it returned to baseline values at 54+/-10 mmHg (27+/-14%). THRR significantly dropped to 11+/-12% at 34+/-11 mmHg when resting cerebral blood-flow velocity levels also started to decline. Based on the close correlation between blood-flow velocity levels and THRR responses, we have concluded that carotid compression is an alternative technique that can be used to assess cerebral autoregulation in rats. The technique allows less invasive and reversible testing of dynamic autoregulation to be performed, and the technique can easily be applied in conjunction with functional tests to potentially allow deeper insights into cerebral vasoregulative mechanisms.

Algorithms↗
PubMed2002

Fundamentals of capillary electrochromatography: migration behavior of ionized sample components.

The mechanism of separating charged species by capillary electrochromatography (CEC) was modeled with the conditions of ideal/linear chromatography by using a simple random walk. The most novel aspect of the work rests with the assumption that in sufficiently high electric field ionized sample components can also migrate in the adsorbed state on the ionized surface of the stationary phase. This feature of CEC leads to the introduction of three dimensionless parameters: alpha, reduced mobility of a sample component with the electrosmotic mobility as the reference; beta, the CEC retention factor; and gamma, the ratio of the electrophoretic migration velocity and the velocity of surface electrodiffusion. Since the interplay of retentive and electrophoretic forces determines the overall migration velocity, the separation mechanism in CEC is governed by the relative importance of the above parameters. The model predicts conditions under which the features of the CEC system engender migration behavior that manifests itself in a relatively narrow elution window and in a gradient like elution pattern in the separation of peptides and proteins by using pro forma isocratic CEC. It is believed that such elution patterns, which resemble those obtained by the use of external gradient of the eluent, are brought about by the formation of an internal gradient in the CEC system that gave rise to concomitant peak compression. The peculiarities of CEC are discussed in the three operational modalities of the technique: co-current, countercurrent, and co-counter CEC. The results suggest that CEC, which is often called "liquid chromatography on electrophoretic platform" is an analytical tool with great potential in the separation of peptides and proteins.

Algorithms↗