Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Data Compression”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,261 records · Page 70Linked to original sources
PubMed2007

Reconstruction domain compression of phase-shifting digital holograms.

Phase-shifting digital hologram compression has been mainly studied in the recording domain, where data possess a rather randomlike appearance, yielding reduced compression efficiency. We carry out the compression of such data in the reconstruction domain, which benefits from the spatial correlation of the data yielding, increased efficiency. Real holographic data are used to demonstrate the performance of the new approach. It is also shown that the reconstruction is not limited to the initially obtained view, as additional views can still be obtained with appropriate postprocessing.

Journal Article↗
PubMed1991

Low-cost, high-sensitivity laser-induced fluorescence detection for DNA sequencing by capillary gel electrophoresis.

A low cost, 0.75-mW helium neon laser, operating in the green region at 534.5 nm, is used to excite fluorescence from tetramethylrhodamine isothiocyanate-labelled DNA fragments that have been separated by capillary gel electrophoresis. The detection limit (3 sigma) for the dye is 500 ymol [1 yoctomole (1 ymol) = 10(-24) mol] or 300 analyte molecules in capillary zone electrophoresis; the detection limit for labeled primer separated by capillary gel electrophoresis is 2 zmol [1 zeptomole (1 zmol) = 10(-21) mol]. The Richardson-Tabor peak-height encoded sequencing technique is used to prepare DNA sequencing samples. In 6% T, 5% C acrylamide, 7 M urea gels, sequencing rates of 300 bases/hour are produced at an electric field strength of 200 V/cm; unfortunately, the data are plagued by compressions. These compressions are eliminated with addition of 20% formamide to the sequencing gel; the gel runs slowly and sequencing data are generated at a rate of about 70 bases/hour.

Base Sequence↗
PubMed2006

Wavelet-based low-delay ECG compression algorithm for continuous ECG transmission.

The delay performance of compression algorithms is particularly important when time-critical data transmission is required. In this paper, we propose a wavelet-based electrocardiogram (ECG) compression algorithm with a low delay property for instantaneous, continuous ECG transmission suitable for telecardiology applications over a wireless network. The proposed algorithm reduces the frame size as much as possible to achieve a low delay, while maintaining reconstructed signal quality. To attain both low delay and high quality, it employs waveform partitioning, adaptive frame size adjustment, wavelet compression, flexible bit allocation, and header compression. The performances of the proposed algorithm in terms of reconstructed signal quality, processing delay, and error resilience were evaluated using the Massachusetts Institute of Technology University and Beth Israel Hospital (MIT-BIH) and Creighton University Ventricular Tachyarrhythmia (CU) databases and a code division multiple access-based simulation model with mobile channel noise.

Algorithms↗
PubMed2004

Modelling the mechanical properties of single suspension-cultured tomato cells.

BACKGROUND AND AIMS: The relationship between composition and structure of plant primary cell walls, and cell mechanical properties is not fully understood, partly because intrinsic properties of walls such as Young's modulus cannot be obtained readily. The aim of this work is to show that Young's modulus of walls of single suspension-cultured tomato cells can be determined by modelling force-deformation data. METHODS: The model simulates the compression of a cell between two flat surfaces, with the cell treated as a liquid-filled sphere with thin compressible walls. The cell wall and membrane were taken to be permeable, but the compression was so fast that water loss could be neglected in the simulations. Force-deformation data were obtained by compressing the cells in micromanipulation experiments. RESULTS: Good fits were obtained between the model and low-strain experimental data, using the modulus and initial inflation of the cell as adjustable parameters. The mean Young's modulus for 2-week-old cells was found to be 2.3 +/- 0.2 GPa at pH 5. This corresponds to an instantaneous bulk modulus of elasticity of approx. 7 MPa, similar to a value found by the pressure probe method. However, Young's modulus is a better parameter, as it should depend only on the composition and structure of the cell wall, not on bulk cell behaviour. This new method has been used to show that Young's modulus of cultured tomato cell walls is at its lowest at pH 4.5, the pH optimum for expansin activity. CONCLUSIONS: The linear elastic model is very suitable for estimating wall Young's modulus from micromanipulation experiments on single tomato cells. This is a powerful method for determining cell wall material properties.

Biomechanical Phenomena↗
PubMed2001

Visualization and interactive analysis of blood parameters with InfoZoom.

This paper describes the application of the data analysis tool InfoZoom to a database containing the results of blood examinations for about 400 patients with a suspect of thrombosis. The main goal was to find correlations between the measurements and the occurrence of a thrombosis. No automatic method for data mining is used. Instead, InfoZoom uses a novel technique to display data sets as highly compressed tables which always fit completely onto the screen. The user can interactively explore animated tabular views of the data. In this way, the user gets a feeling of the data, detects interesting knowledge, and gains a deep understanding of the data set.

Databases, Factual↗
PubMed1995

Intermittent cauda equina compression. An experimental study of the porcine cauda equina with analyses of nerve impulse conduction properties.

STUDY DESIGN: Neurophysiologic reactions of cauda equina nerve roots to intermittently applied compression were assessed for two different modes of compression using a porcine model. OBJECTIVE: To assess the neurophysiologic reactions of cauda equina nerve roots to intermittently applied compression. SUMMARY OF BACKGROUND DATA: A number of experimental studies have been presented recently regarding the reaction pattern of spinal nerve roots to compression. These studies have used a continuous pressure level. For studies of pathophysiologic mechanisms behind neurogenic claudication, however, it would be more relevant to study the effects of intermittently applied compression. METHODS: The cauda equina was exposed and compression was applied by two inflatable balloons. Two different modes of compression were used. Either the two balloons were inflated and deflated simultaneously (intermittent compression), or just the caudal balloon was inflated and deflated while the cranial balloon was kept continuously inflated (continuous/intermittent compression). The experimental series were: intermittent compression at 10 mm Hg (n = 5) and 50 mm Hg (n = 5), and continuous/intermittent compression at 10 mm Hg (n = 5) and 50 mm Hg (n = 5). For both modes of compression the pressure in the balloons with intermittent inflation was maintained for 10 minutes and deflated for 5 minutes. This procedure was repeated in 8 cycles for 2 hours. Muscle action potentials were recorded in the tail muscles. RESULTS: Compression at 10 mm Hg induced similar reductions of muscle action potentials for both compression modes. At 50 mm Hg, the effects were more pronounced at continuous/intermittent compression than at intermittent compression. The reduction of muscle action potentials was slightly more pronounced for 50 than for 10 mm Hg at intermittent compression. However, a statistically significant difference in the results was found only between 10 and 50 mm Hg at the continuous/intermittent compression mode. CONCLUSIONS: The established model allows investigation of the effects of intermittent cauda equina compression, which might be clinically more relevant than continuous compression regarding the pathophysiologic mechanisms behind neurogenic claudication.

Action Potentials↗
PubMed1989

[Value of hemodynamics in the surgical indications of emphysema].

The authors present the results of a preliminary study designed to define the surgical indications in diffuse pulmonary emphysema based on the data of haemodynamic investigations. This series consists of 10 patients identified for disabling dyspnoea, diffuse emphysema and dynamic expiratory compression documented by the data of right micro-catheterisation by a DEP/DIP ratio greater than 2. The surgical operation consisted of reduction in the lung volume, the results of which were defined by pre- and postoperative examinations. In this way, it is possible to distinguish 3 groups of patients: one group was markedly improved, another was moderately improved and the third group continued to deteriorate analysis of the results suggests the determinant role of dynamic factors, in particular haemodynamic factors. The role of the diaphragm is demonstrated by modifications in its radius or curvature.

Diaphragm↗
PubMed2004

Biomechanical and perceptual constraints on the bandwidth requirements of sign language.

Access to telecommunication systems by deaf users of sign language can be greatly enhanced with the incorporation of video conferencing in addition to text-based adaptations. However, the communication channel bandwidth is often challenged by the spatial requirements to represent the image in each frame and temporal demands to preserve the movement trajectory with a sufficiently high frame rate. Effective systems must balance the portion of a limited channel bandwidth devoted to the quality of the individual frames and the frame rate in order to meet their intended needs. Conventional video conferencing technology generally addresses the limitations of channel capacity by drastically reducing the frame rate, while preserving image quality. This produces a jerky image that disturbs the trajectories of the hands and arms, which are essential in sign language. In contrast, a sign language communication system must provide a frame rate that is capable of representing the kinematic bandwidth of human movement. Prototype sign language communication systems often attempt to maintain a high frame rate by reducing the quality of the image with lossy spatial compression. Unfortunately, this still requires a combined spatial and temporal data rate, which exceeds the limited channel of residential and wireless telephony. While spatial compression techniques have been effective in reducing the data, there has been no comparable compression of sign language in the temporal domain. Even modest reductions in the frame rate introduce perceptually disturbing flicker that decreases intelligibility. This paper introduces a method through which temporal compression on the order of 5:1 can be achieved. This is accomplished by decoupling the biomechanical or kinematic bandwidth necessary to represent continuous movements in sign language from the perceptually determined critical flicker frequency.

Adult↗
PubMed2006

Effects of oil on the curvature elastic properties of nonionic surfactant films: thermodynamics of balanced microemulsions.

The free energy of nonionic balanced microemulsions based on nonionic surfactants are analyzed using experimental data from (i) phase behavior, (ii) osmotic compressibility of the balanced microemulsion structure, which is obtained from small angle neutron scattering (SANS) experiments, and (iii) data on interfacial tensions obtained by T. Sottmann and R. Strey [J. Chem. Phys. 106 8606 (1997)]. The balanced microemulsion, where the spontaneous curvature vanishes at equal volumes of water and oil, has a finite swelling with the solvent with a minimum surfactant volume fraction, Phi*(S). At higher surfactant concentrations the balanced microemulsion phase having the surfactant volume fraction Phi(S1) coexists with a lamellar phase of volume fraction Phi(S2). Under the constraint of Phi(W) = Phi(O), where Phi(W) and Phi(O) are the water and oil volume fractions, respectively, the free energy density can be written as an expansion in the surfactant concentration. While the phase equilibria only depend on relative values of the expansion coefficients, absolute values can be obtained from compressibility and interfacial tension data. The osmotic compressibility of the surfactant film was measured by SANS through contrast matching water and oil. The phase behavior of nonionic surfactant-water-oil systems depends strongly on the chain length of the oil, when comparing a homologous series from octane to hexadecane using the same surfactant, here being pentaethylene oxide dodecyl ether (C(12)E(5)). The three concentrations Phi*(S), Phi(S1), and Phi(S2) increase markedly as the chain length of the oil is increased. However, from the analysis of the surface tension data it is concluded that there are no major changes in the bending rigidities as the oil is changed. The data are analyzed within the model free energy densities [formula--see text] and [formula--see text]. We find that within experimental accuracy, the first of these models provides a quantitatively consistent description of the data. For the second model there is a larger discrepancy between observed and calculated values.

Journal Article↗
PubMed1999

Human growth hormone transgene expression increases the biomechanical structural properties of mouse vertebrae.

STUDY DESIGN: Caudal vertebrae were obtained from male and female mice from two transgenic lines expressing an erythroid-specific human growth hormone transgene construct, and gender-matched, age-matched, non-transgenic control mice. OBJECTIVE: To characterize the effect of human growth hormone transgene expression on the biomechanical structural properties of caudal vertebrae in compression. SUMMARY OF BACKGROUND DATA: An increase in trabecular and cortical bone deposition caused by erythroid-specific human growth hormone transgene expression was demonstrated previously. METHODS: Compression tests were performed on individual caudal vertebrae (Ca4, Ca5, Ca6) obtained from male and female mice from two transgenic lines (TG420 and TG450) and nontransgenic control mice. Two age groups were evaluated: 12 weeks old and 6 months old. The data were used to obtain axial stiffness, maximum load, and energy to failure. RESULTS: Vertebrae from male TG420 transgenic mice produced significantly larger values for maximum load, energy to failure, and axial stiffness at both 12 weeks and 6 months in comparison with their age-matched non-transgenic male controls. Vertebrae from female TG420 transgenic mice produced similar responses at 6 months. Vertebrae from male TG450 transgenic mice showed significant increases in maximum load and energy to failure at 6 months. In general, the biomechanical properties of vertebrae were significantly larger in the 6-month age group than in the 12-week age group, and this increase was significantly greater in the transgenic mice than in the gender-matched control mice during the same time span. This process was also influenced by transgenic genotype and gender. CONCLUSIONS: Erythroid-specific production of human growth hormone in transgenic mice resulted in significant increases in biomechanical properties of their caudal vertebrae in compression. The changes in the biomechanical properties were influenced by genotype, age, and gender.

Aging↗
PubMed1990

Identification of dynamic mechanical parameters of the human chest during manual cardiopulmonary resuscitation.

Survival from cardiac arrest is dependent on timely cardiopulmonary resuscitation (CPR). Since CPR is often unsuccessful, the outcome may be improved by a better understanding of the relationship between force applied to the sternum and the resulting hemodynamic effects. The first step in this complex chain of interactions is the mechanical response of the chest wall to cyclical compression. We formulated a dynamic mechanical model of the chest response and developed a method of identification of the model parameters based on force, displacement, and acceleration data acquired during cyclical compressions. The elasticity, damping, and equivalent mass of the human chest were estimated with a constrained nonlinear least-mean-square identification technique. The method was validated on data acquired from a test apparatus built for this purpose. The model fit was measured with the normalized chi-square statistic on residuals obtained between recorded force and force predicted by the model. In the analysis of one human chest, the elasticity was found to be nonlinear and statistically different during compression and release. A considerable amount of damping was found, with no significant difference between compression and release. The equivalent mass was too small to be determined accurately. This method can be used to obtain the dynamic mechanical parameters of the human chest and may lead to a better understanding of CPR.

Biomechanical Phenomena↗
PubMed2002

Modeling of gas absorption cross sections by use of principal-component-analysis model parameters.

Monitoring the amount of gaseous species in the atmosphere and exhaust gases by remote infrared spectroscopic methods calls for the use of a compilation of spectral data, which can be used to match spectra measured in a practical application. Model spectra are based on time-consuming line-by-line calculations of absorption cross sections in databases by use of temperature as input combined with path length and partial and total pressure. It is demonstrated that principal component analysis (PCA) can be used to compress the spectrum of absorption cross sections, which depend strongly on temperature, into a reduced representation of score values and loading vectors. The temperature range from 300 to 1000 K is studied. This range is divided into two subranges (300-650 K and 650-1000K), and separate PCA models are constructed for each. The relationship between the scores and the temperature values is highly nonlinear. It is shown, however, that because the score-temperature relationships are smooth and continuous, they can be modeled by polynomials of varying degrees. The accuracy of the data compression method is validated with line-by-line-calculated absorption data of carbon monoxide and water vapor. Relative deviations between the absorption cross sections reconstructed from the PCA model parameters and the line-by-line-calculated values are found to be smaller than 0.15% for cross sections exceeding 1.27 x 10(-21) cm(-1) atm(-1) (CO) and 0.20% for cross sections exceeding 4.03 x 10(-21) cm(-1) atm(-1) (H2O). The computing time is reduced by a factor of 10(4).

Journal Article↗
PubMed2003

Potential margin distortion in breast tissue by specimen mammography.

HYPOTHESIS: There is a potential for margin distortion associated with the use of a compression plate in specimen mammography (SM) devices. DESIGN: Prospective observational study. SETTING: Two tertiary care teaching hospitals. PATIENTS: Breast biopsy tissue dimensions were recorded in 15 patients undergoing 18 operations before and after SM (group 1). After review of these data, we supervised the positioning of tissue for SM and obtained measurements for 12 breast biopsy specimens from 12 additional patients before and after SM (group 2). MAIN OUTCOME MEASURES: Breast biopsy specimen dimensions recorded before and after SM, including length, width, and depth (the specimen depth along the axis of compression); data on age, menopausal status, hormone therapy, and the presence or absence of calcifications or tumor; and a national telephone survey on technique and understanding of SM at 21 institutions. RESULTS: The specimen depth in group 1 was markedly decreased (P<.001) along the axis of compression. The mean length and width of the specimens were marginally increased by the effect of the SM device. Specimen depth in group 2 was unchanged when minimal pressure was used on the compression plate. Tissue was adequately immobilized in both groups, and all lesions were identified by SM. Our survey revealed that 71% of hospitals reported using firm compression in SM, and diverse techniques were employed. CONCLUSIONS: This study demonstrates the potential for specimen margin distortion with compression SM. Undue specimen compression is common in routine SM. Surgeon oversight in the method of securing the specimen within the SM container will minimize or avoid the potential for margin distortion.

Biopsy↗
PubMed1994

Thermocycling--the effects upon the compressive strength and abrasion resistance of three composite resins.

The purpose of this investigation was to examine the effects of thermocycling upon the compressive strength and abrasive wear resistance of three commercial composites Fulfil, P-50 and Herculite-XR. Specimens of each material were divided into five treatment groups comprising a control, and four different cycling and storage regimes. Tests for compressive strength and wear resistance were carried out. Prior to testing all specimens were stored in distilled water for 1 week. Three groups were stored at a temperature of 37 degrees C and the remaining two at 60 degrees C. Thereafter all groups that were thermocycled were subjected to 750 cycles of a thermocycling regime consisting of the cycle ACAB where A and B represent the fixed temperatures of 37 degrees C and 5 degrees C, and C, depending upon the treatment group, either 50 degrees C or 60 degrees C. One-way analyses of variance upon the compressive strength and wear factor data following the treatments highlighted significant differences in the mean compressive strength for all materials (Fulfil (P < 0.05), P-50 and Herculite-XR (P < 0.01)) and in the wear factor values for only Fulfil and P-50 (P < 0.001). Surprisingly, thermocycling P-50 with an upper temperature limit of 50 degrees C had catastrophic consequences upon the measured properties. It is concluded that some of the observed behaviour may have potentially detrimental consequences upon the long-term clinical durability of the materials tested.

Analysis of Variance↗
PubMed1988

Gray level transforms and lesion detectability in echographic images.

In search of the optimal display of echographic information for the detection of focal lesions, a systematic study was performed considering a wide range of gray level transforms (i.e., lookup tables). This range comprised power functions of the echo envelope signal (1/8 less than or equal to n less than or equal to 8), power functions of the logarithmic transform and a sigmoid function. The implications of the transforms on the first order statistics (histogram, "point signal-to-noise ratio" SNRp) and on the second order statistics (autocorrelation function) could be derived both analytically, and from the analysis of simulated and experimentally obtained echograms of homogeneously scattering tissue models. These results were employed to estimate the lesion signal-to-noise ratio SNRl, which specifies the detectability of a lesion by an ideal observer. It was found, both theoretically and practically, that the intensity display corresponds to the optimal transform (i.e., n = 2) for a low contrast lesion. When the data were first logarithmically compressed, the lesion SNR appeared to increase with increasing power (1/8 less than or equal to n less than or equal to 8). A logarithmic transform followed by a sigmoid compression did not produce much improvement. These effects of gray level transforms on the SNRl were shown to be relatively small, with the exception of powers n greater than 2 when applied to linear (i.e. amplitude) data. In the case of high lesion contrast, the sequence of log compression, followed by a square law produced the optimum SNRl. This sequence is equivalent to the processing within echographic equipment, where the TV monitor has a gamma of the order of 2.

Computer Simulation↗
PubMed2006

Recent changes in the spatial pattern of prostate cancer in the U.S.

INTRODUCTION: Spatial-temporal trends in prostate cancer mortality are of interest because of the introduction and increasing use of the prostate-specific antigen (PSA) screening test after 1986. This article describes spatial-temporal changes in U.S. prostate cancer mortality from 1968 to 1998. METHODS: Prostate cancer mortality data were obtained from Compressed Mortality Files available from the National Center for Health Statistics. To minimize potential problems such as small numbers or missing data, the analysis was limited to white males aged 25 and over, and located in 2970 counties with complete data. Statistical analyses included the global distance between observed and expected multinomial probabilities, Hoover's Index of Concentration, and a retrospective test for change in spatial patterns. RESULTS: Fairly steady declines were observed in prostate cancer mortality from 1968 until 1993, with an increasing tendency toward spatial uniformity. Spatial concentration increased from 1994 to 1998, and by 1998 the level of spatial concentration had returned to levels that prevailed during the early to mid-1980s. Comparing 1991-1998 to 1968-1990, the observed number of prostate deaths increased the most rapidly with respect to the expected number in western Appalachia and the south central U.S. Recent relative declines in mortality were observed in southern California and parts of Florida. CONCLUSIONS: The observed results are generally consistent with prior evaluations of prostate cancer spatial-temporal patterns. However, the current study identified a heretofore unnoticed recent pattern of change in western Appalachia and the south central U.S. Recent declines in Florida and southern California may have contributed to recent increases in spatial concentration of prostate cancer mortality, and may possibly be associated with realized benefits from screening programs.

Aged↗
PubMed2001

Time-resolved X-ray diffraction by skinned skeletal muscle fibers during activation and shortening.

Force, sarcomere length, and equatorial x-ray reflections (using synchrotron radiation) were studied in chemically skinned bundles of fibers from Rana temporaria sartorius muscle, activated by UV flash photolysis of a new photolabile calcium chelator, NP-EGTA. Experiments were performed with or without compression by 3% dextran at 4 degrees C. Isometric tension developed at a similar rate (t(1/2) = 40 +/- 5 ms) to the development of tetanic tension measured in other studies (Cecchi et al., 1991). Changes in intensity of equatorial reflections (I(11) t(1/2), 15-19 ms; I(10) t(1/2), 24-26 ms) led isometric tension development and were faster than for tetanus. During shortening at 0.14P(o), I(10) and I(11) changes were partially reversed (18% and 30%, respectively, compressed lattice), in agreement with intact cell data. In zero dextran, activation caused a compression of A-band lattice spacing by 0.7 nm. In 3% dextran, activation caused an expansion of 1.4 nm, consistent with an equilibrium spacing of 45 nm. But, in both cases, discharge of isometric tension by shortening caused a rapid lattice expansion of 1.0-1.1 nm, suggesting discharge of a compressive cross-bridge force, with or without compression by dextran, and the development of an additional expansive force during activation. In contrast to I(10) and I(11) data, these findings for lattice spacing did not resemble intact fiber data.

Animals↗
PubMed1981

Effect of external pressure on axillofemoral bypass grafts.

External compression of axillofemoral grafts has been suggested many times as a cause for graft thrombosis. Thrombosis during sleep is the most common presentation of axillofemoral graft failure. Therefore, external compression of the graft by the body weight has been implicated in graft thrombosis. Six consecutive patients with axillofemoral bypass grafts for aortoiliac disease were studied on routine clinic visits. Pulsatile flow characteristics were studied by pulse volume recordings (PVR) and segmental Doppler pressure measurements in calf and ankle, prior to and during attempted graft compression, by having the patient lay on the graft. External compression by body weight did not alter the PVR and segmental Doppler pressure (P = NS) in the distal circulation. Therefore, these data suggest that external compression by the body weight may not be the primary cause of graft failure.

Axillary Artery↗