Enhancements in laser-generated hot-electron production via focusing cone targets at short pulse and high contrast.

We report on the increase in the accelerated electron number and energy using compound parabolic concentrator (CPC) targets from a short-pulse (∼150 fs), high-intensity (>10^{18} W/cm^{2}), and high-contrast (∼10^{8}) laser-solid interaction. We report on experimental measurements using CPC targets where the hot-electron temperature is enhanced up to ∼9 times when compared to planar targets. The temperature measured from the CPC target is 〈T_{e}〉=4.4±1.3 MeV. Using hydrodynamic and particle in cell simulations, we identify the primary source of this temperature enhancement is the intensity increase caused by the CPC geometry that focuses the laser, reducing the focal spot and therefore increasing the intensity of the laser-solid interaction, which is also consistent with analytic expectations for the geometrical focusing.

Experiment and simulation of novel liquid crystal plasma mirrors for high contrast, intense laser pulses.

We describe the first demonstration of plasma mirrors made using freely suspended, ultra-thin films formed dynamically and in-situ. We also present novel particle-in-cell simulations that for the first time incorporate multiphoton ionization and dielectric models that are necessary for describing plasma mirrors. Dielectric plasma mirrors are a crucial component for high intensity laser applications such as ion acceleration and solid target high harmonic generation because they greatly improve pulse contrast. We use the liquid crystal 8CB and introduce an innovative dynamic film formation device that can tune the film thickness so that it acts as its own antireflection coating. Films can be formed at a prolonged, high repetition rate without the need for subsequent realignment. High intensity reflectance above 75% and low-field reflectance below 0.2% are demonstrated, as well as initial ion acceleration experimental results that demonstrate increased ion energy and yield on shots cleaned with these plasma mirrors.

Chlamydia pneumoniae and cardiovascular disease: an evolutionary perspective on infectious causation and antibiotic treatment.

Evolutionary considerations implicate infectious causation of atherosclerosis and help to resolve different risk factors as parts of an overall process of disease causation. An evolutionary approach also provides insight for the timing of research efforts to provide better control of pathogen evolution. In particular, evolutionary considerations emphasize the need to understand the transmissibility of Chlamydia pneumoniae from systemic infections in order to control the evolution of antibiotic resistance.

Streaming potentials in gap osteotomy callus and adjacent cortex. A pilot study.

This study documented streaming potentials generated in vivo by maturing osteotomy calluses in 10 canine tibiae. Gap osteotomies were allowed to heal for 6 or 12 weeks and were stabilized by an external fixator. Then, with the dogs under anesthesia, electrical measurements were made from 3 silver-silver chloride electrodes placed surgically in direct contact with the callus, with adjacent cortical bone, and with the medullary canal (reference electrode). Streaming potentials were recorded during step loading and sinusoidal bending (0.1-30 Hertz) as the tibia was deformed by 2 threaded pins coupled to a servohydraulic device. Streaming potentials were generated at callus and adjacent cortical sites, but the magnitude was greater on the immature, flexible callus, where bending strain was concentrated; as the callus became increasingly rigid, strain and streaming potential magnitude were distributed more evenly over the callus and adjacent cortical fragments. When normalized to surface strain, mean streaming potential per strain was less dependent on the microscopic structure, although on individual specimens streaming potential per strain at callus and adjacent cortical bone sites tended to increase with decreasing porosity. Despite a wide variation in data in this pilot series, these observations are consistent with the natural history of callus maturation: the maximum magnitude of streaming potentials in callus appears to decrease as the strain gradient across the site decreases, whereas streaming potentials normalized to strain increase as bone matures and becomes more dense.

Comparison of molecular cytokeratin 19 reverse transcriptase polymerase chain reaction (CK19 RT-PCR) and immunocytochemical detection of micrometastatic breast cancer cells in hematopoietic harvests.

Detection of small numbers of breast cancer cells in patient blood, aphereses, and bone marrow has become increasingly important as data have accumulated showing immunocytochemically (ICC) positive tumor cells in up to 50% of women with stage I and II breast cancer, who were initially thought to be cured of their disease but later relapsed. The ability to rule out the presence of micrometastatic disease at any stage of the clinical management protocol, whether before, during, or after therapy, would provide a useful monitoring and diagnostic tool for both the clinician and the scientist. Monitoring for the presence of minimal residual disease (MRD) is traditionally performed using ICC. A more recently established RT-PCR technique uses a molecular marker (the presence of the cytokeratin 19, CK19, transcript) to identify MRD in patient samples, with a level of sensitivity reported to be one tumor cell in 10(6) nucleated cells. This level of sensitivity is generally higher than that claimed for ICC. Based on the discriminating results of this first study, a number of laboratories have evaluated this technique for its diagnostic potential. Results from several laboratories showed a higher than expected false positive rate due to a variety of identified and unidentified sources. Therefore, the current study was designed to achieve two aims: to establish the level of sensitivity and specificity of the RT-PCR technique and to dissect out the possible variables that may contribute to a false positive result using this molecular approach. To accomplish the first goal, two simulation strategies were used, limited dilution of tumor cells into apheresis harvests and semi-quantitative PCR using stepwise dilutions of extracted RNA from tumor cells in apheresis harvests. The second goal was accomplished by performing sequential blood drawings with variably timed sample processing to identify some of the more common variables (time, anticoagulant, sample sequence) that may contribute to false positive results. Of three variables investigated, including type of blood preservative, sequence of blood tube collection, and time point of sample processing, each may contribute to a false positive result. In addition to these problems, known events involving illegitimate transcription of specific genes nonspecifically in tissue is also a potential source of false positive results. These issues may be further compounded by lack of attention to the more common methodologic problems encountered in any laboratory using the PCR technique. However, recommendations can be developed for the effective application of this technique, whose greatest strength is the demonstration of tumor negativity of the sample.

Characterization of a new lectin of soybean vegetative tissues.

Lectins are carbohydrate-binding proteins that occur widely among plants. Lectins of plant vegetative tissues are less well characterized than those of seeds. Previously, a protein of soybean (Glycine max [L.] Merr.) leaves was shown to possess properties similar to the seed lectin. Here we show that the N-terminal amino acid sequence of this protein shares 63% identity with the seed lectin. Immunoblot analysis indicated that the protein occurs in leaves, petioles, stems, and cotyledons of seedlings but not in seeds. These observations prompted designation of the protein as a soybean vegetative lectin (SVL). Immunohistochemical localization in leaves indicated that SVL was localized to the vacuoles of bundle-sheath and paraveinal mesophyll cells. Removal of sink tissues or exposure to atmospheric methyl jasmonate caused increased levels of SVL in leaves and cotyledons. Co-precipitation of SVL and the soybean vegetative storage protein (VSP) during purification suggested an interaction between these proteins. SVL-horseradish peroxidase conjugate bound to dot blots of VSP or SVL, and binding was inhibited by porcine stomach mucin and heparin but not simple carbohydrates. Binding between SVL and VSP and similarities in localization and regulation support a possible in vivo interaction between these proteins.

Inflatable brace-related streaming potentials in living canine tibias.

In a canine osteotomy model, application of a pressurized brace increased the density of periosteal bone and, at 12 weeks postfracture, yielded a stronger union compared with fractures treated by conventional cast, as determined by biomechanical testing. Pulsatile transcortical electric potentials were caused by the fluctuations in intramedullary pressure that result from active circulation. This report describes a collaborative effort designed to determine whether pressure fluctuations within an inflatable brace, placed over a canine calf, can affect endogenous transcortical electric potentials. Pressure within a brace placed over a canine hindlimb was observed to oscillate between 20 and 52 mm Hg during normal ambulation in 3 dogs. Manual pulsatile inflation of a similar brace, causing brace pressure fluctuations between 12 mm Hg and 130 mm Hg, produced fluctuating transcortical electric potentials ranging from 1.2 microvolts to 87 microvolts in anesthetized canines. These electric potentials were proportional to intramedullary pressures between 3.4 mm Hg and 59 mm Hg. Transcortical electric potentials resulting from the application of a pressurized brace, rather than conventional casting, may be part of the mechanism by which the changes in fracture healing are achieved.

Streaming potential measurements at low ionic concentrations reflect bone microstructure.

Streaming potentials (SPs) have been proposed as one transduction pathway for mechanically driven bone remodeling. The fluid spaces in which SPs are generated will determine, in part, the structural information that they can provide to bone cells. Streaming potential measurements across cortical bone strips soaked in a range of saline concentrations were used to estimate the mean radii of fluid spaces that contribute to generation of electrokinetic fields. Using a cylindrical pore model, a pore radius of less than 200 A fit SP magnitude as a function of concentration. This pore size was shown to be consistent with estimates obtained from data reported earlier for SP as a function of concentration using a non-specific model, but was smaller than previously reported estimates for pore radius. A pore size in this range indicates that flow either in bone microporosity, or canaliculi that are substantially occluded by cellular material, must generate streaming potentials. Further, the fact that such small pores generate SPs in bone indicates that SPs could provide information regarding local matrix structure to bone cells.

Aramid-epoxy composite internal fixation plates: a pilot study.

Mechanical tests were conducted on an aramid-epoxy composite laminate in vitro and in vivo to determine its suitability for internal fixation plates. This material, fashioned into blank test coupons the size of the standard 4-hole AO-ASIF plates, had a tensile modulus of elasticity significantly lower than bone. In three-point bending, blank test coupons exhibited a low yield strength that would limit utility in significant load-bearing situations, but changes in the layer configuration of the composite could be expected to improve this characteristic. Under destructive loads, these specimens appeared to be less subject to catastrophic failure than carbon fibre composites. Using 4-hole test coupons fastened to a plastic tube simulating bone, four-point bending tests showed that strain-shielding was significantly reduced by aramid composite relative to carbon fibre composite or metal plates. Finally, in-vivo tests on canine femora demonstrated that aramid composite plates were well tolerated and caused less strain shielding during weightbearing, but significant differences in cortical atrophy and porosity beneath steel versus aramid plates were not apparent. Although the plates were relatively flexible, they could not be preformed during surgery like a metal plate.

Intraarterial protamine sulfate reduces the magnitude of streaming potentials in living canine tibia.

Using previously described techniques, transcortical streaming potentials were measured at two middiaphyseal sites on one tibia of each of nine anesthetized canines during sinusoidal bending (approximately 0 to -200 mu epsilon periosteal surface strain) at 2 Hz. Measurements were made for 60 minutes prior to and up to 180 minutes following bolus injection of protamine sulfate (42-126 mg/kg) dissolved in Hanks Balanced Salt Solution, directly into the femoral artery without interrupting circulation. Shortly after injection, the protamine sulfate caused a clear reduction in the magnitude of streaming potentials. Subsequent injections of additional protamine sulfate resulted in further reductions, and in several instances, voltage sign reversals. This study represents the first observation that circulating proteins may alter electromechanical transduction in living bone, and suggests the possibility that specific agents, which are known to affect bone remodeling, may do so, in part, by altering these endogenous electrical potentials.

Streaming potentials in healing, remodeling, and intact cortical bone.

Electrical fields have been implicated in accelerated bone healing and as a transduction mechanism for mechanically driven bone remodeling. Applied mechanical or electrical stimulation of bone remodeling suggests that this depends on the magnitude, frequency, and duration of the stimulus. The magnitude of endogenous electrical fields, manifest by streaming potentials (SPs) across canine cortical bone, were measured as a function of bending frequency in vivo and then in vitro at healing drill holes and at remodeling (ipsilateral) and normal, intact (contralateral) control sites in canine tibia. SP magnitudes normalized to periosteal strain were smaller for drill holes at 2 and 4 weeks postsurgery relative to either remodeling (P < 0.05 at 10 Hz) or normal intact (P < 0.001 at 10 Hz) controls both in vivo and in vitro. SPs of 12 week drill holes were similar to SPs of remodeling controls and tended to be smaller than SPs of normal intact controls. Mean SP normalized to bone impedance was approximately the same for all sites, suggesting that the smaller SPs during healing and remodeling relate to smaller bone impedance and/or larger porosity. SP as a function of bending frequency for normal sites was similar to that observed previously. SP versus frequency for drill holes and remodeling controls was more variable, probably because of variations in bone microstructure, and displayed a higher frequency content. The observed differences in SP magnitude and frequency response to loading associated with stages of healing indicate that endogenous electrical fields do indeed respond to the structural changes in healing and remodeling and are therefore capable of providing structural feedback information for the repair and remodeling process.

Relationships between bone structure in the iliac crest and bone structure and strength in the lumbar spine.

The purpose of this study was to examine the relationship between histomorphometric variables of cancellous bone structure and ultimate compressive strength (UCS) in the second lumbar vertebra (L2) and to determine whether structural variables in the iliac crest are predictive of the same variables and of UCS in L2. At autopsy, 7.5 mm diameter cores were removed from the iliac crest and from L2 of 29 subjects who had died suddenly without bone disease. Cancellous bone volume (BV/TV, %) was significantly lower in L2 than in iliac crest due to lower trabecular number (Tb.N, per mm) and thickness (Tb.Th, microns). There were significant correlations between iliac crest and L2 for BV/TV, Tb.N and trabecular separation (Tb.Sp, microns), but not for Tb.Th. BV/TV was negatively correlated, and Tb.Sp was positively correlated with age at both sites. Tb.Th was not significantly correlated with age in the iliac crest, but a significant negative correlation was observed in L2. The UCS of vertebral cores was negatively correlated with age. BV/TV and Tb.Th in L2 were positively correlated with UCS in L2.(ABSTRACT TRUNCATED AT 250 WORDS)

A comparative analysis of streaming potentials in vivo and in vitro.

Streaming potentials (SPs) measured in vivo at a specific site on intact cortical bone (canine tibia) have been compared with measurements from the same site in vitro, tested as an excised bone strip soaked in Hank's balanced salt solution. The amplitude of SPs per periosteal strain in vitro was larger in 13 tibias than in vivo (by an average x6.5 at 1 Hz), but values per transcortical strain difference were similar. In vitro, SP magnitudes rose more sharply to an asymptotic value as a function of bending frequency than did in vivo signals, possibly because of a difference in the internal state of canaliculi and/or Haversian systems. Similarly, SP response to step-loading decreased to zero more slowly with time in vitro than in vivo. Difficulties encountered in preliminary measurements due to electrical shunting through electrolyte and soft tissues suggest the need for caution in using both in vivo and in vitro SP measurements to extrapolate to electric field strengths on the cellular level.

Leptospira interrogans serovar bratislava infection in two dogs.

Two dogs with clinical histories suggestive of leptospirosis were examined serologically and culturally for evidence of leptospiral infection. Antibodies to Leptospira interrogans serovar bratislava were detected in serum from one dog, and the organism was isolated from urine of that dog. In a serologic survey of dogs in the state of Illinois, reactor rates to bratislava were higher than those to canicola or icterohaemorrhagiae. In cases of suspect canine leptospirosis, serovars such as bratislava, not contained in canine vaccines, should be considered in a differential diagnosis.

A new manual method for assessing two-dimensional cancellous bone structure: comparison between iliac crest and lumbar vertebra.

We have developed a simple method for the direct analysis of two-dimensional trabecular structure. Using this method, we have compared the structure of the left and right iliac crest and the second lumbar vertebra and studied the relationship between two-dimensional trabecular structure and the ultimate compressive stress of bone samples from the second lumbar vertebra. Transverse cores were taken from the left and right iliac crests and second lumbar vertebrae of 35 subjects (12 females) who died suddenly. The trabecular structure was subdivided into nodes (node count) and free ends (free end count), which were expressed per square millimeter of cancellous space. A node was defined as the point of junction between two or more trabeculae; a free end was defined as the end of a trabecula that was unconnected in the plane of the section to any other trabecular element. The following struts were defined by drawing a line between the nodes and the free ends: node to node, node to free end, free end to free end, and cortex-derived struts. Strut lengths were measured and expressed as a percentage of the total strut length and per square millimeter of cancellous space. Intraobserver variation was generally low, with coefficients of variation for repeat measurements in the range 3.9-17.8%. There was no statistically significant difference between left and right iliac crests for any of the variables measured. With the exception of cortex-derived struts, there was no statistically significant correlation between crests for any variable.(ABSTRACT TRUNCATED AT 250 WORDS)

Dynamic electromyography. I. Numerical representation using principal component analysis.

A complete description of human gait requires consideration of linear and temporal gait parameters such as velocity, cadence, and stride length, as well as graphic waveforms such as limb rotations, forces, and moments at the joints and phasic activity of muscles. This results in a large number of interactive parameters, making interpretation of gait data extremely difficult. Statistical pattern recognition techniques can simplify this problem. For this approach to be successful, first it is necessary to reduce the number of interactive parameters to a manageable set. In this study, we present an application of principal component analysis as a means for representing graphic waveforms in a parsimonious manner. In particular, we concentrate on representing the phasic muscle activity recorded using surface electrodes from ten major muscles of the lower extremity of 35 normal subjects during level walking. A 32 point vector is created in which each point of the vector represents the normalized area under the curve of a portion of rectified and smoothed electromyographic signal, expressed as a function of gait cycle. Principal components are computed and the first few weighting coefficients are retained as features to represent the original EMG data. We show that the corresponding basis vectors span parts of the gait cycle where the most variability between individual subjects exists. We also show that the basis vectors can be used to represent the EMG data of subjects not originally used to generate the basis vectors.

Dynamic electromyography. II. Normal patterns during gait.

Human gait is a complex phenomenon. Many descriptors are needed to completely describe gait in terms of the biomechanics involved. The descriptors, when expressed as a function of the gait cycle, are complex waveforms. For each of these variables, a single "normal" pattern with bands of deviation has generally been accepted as a reference in clinical/research use to explain the abnormalities in a patient's walking pattern. In fact, one observes many "normal" patterns, and a body of research has been devoted to explaining the differences between these patterns in terms of walking speed, age, cadence, sex, etc. It would be simpler in one sense to start with the fact that different people walk with different patterns, not one pattern with bands of deviation. Numerical representation of the waveforms simplifies the analysis and interpretation of waveform data and facilitates comparison between subjects or groups of subjects. When combined with pattern recognition techniques, it also is useful for identifying subpatterns within a group. In this article, the numerical representation of electromyographic data by Karhunen-Loeve expansion are combined with cluster analysis to obtain patterns of dynamic phasic activity of 10 muscles of the lower extremity. From the 35 normal subjects walking at self-selected speed, two to four patterns are developed for each of the muscles and the physiological significance of the patterns are discussed.

Transcortical streaming potentials are generated by circulatory pressure gradients in living canine tibia.

Electrical potentials associated with the pulse pressure have been observed in a canine tibia model in vivo. As the medullary pressure rises during pulsing, the periosteal bone surface becomes positive with respect to the endosteal surface. This pattern is consistent with streaming potentials generated by outward flow of fluid through bone with a negatively charged matrix (negative zeta potential). Both the medullary pressure and electric potential oscillations are halted by occlusion of the femoral artery. Furthermore, systemic administration of epinephrine decreases the amplitude of the medullary pressure and the electric potential by the same fraction. Streaming potentials generated by blood flow are distinct from those generated by mechanical deformation and may have additional significance in relation to fracture healing and/or etiology of osteoporosis.