bluuebunny/crossref_metadata_2025 huggingface dataset:
Arthroscopic Mosaic Arthroplasty in the Equine Third Carpal Bone
Authors: Hurtig Mark , Pearce Simon , Warren Stacey , Kalra Manpreet , Miniaci Anthony
Published: August 2002

Objective—To investigate survival and function of autogenous heterotopic osteochondral grafts in a site where injuries are common.

Study Design—Three osteochondral grafts were harvested arthroscopically from the femoropatellar joint and transplanted to the third carpal bone (C3). Nine months later, histologic, histomorphometric, and biochemical comparisons were made between the transplanted grafts in C3and tissue adjacent to the recipient site, the opposing radial carpal bone (Cr), the donor site in the femoropatellar joint, and the sham‐operated contralateral C3.

Animals—One mixed‐breed pony and 5 Standardbred horses aged 3 to 8 years old.

Methods—Using instruments modified for equine use, four 4.5‐mm‐diameter osteochondral grafts were harvested arthroscopically from the distal aspect of the lateral trochlea of the right femur and inserted into the radial facet of the right third carpal bone. The fourth graft was kept as a donor‐site control sample. Three months later, regular exercise was started and at 6 months, repeat arthroscopy was conducted to evaluate healing. The horses were euthanatized 9 months after transplantation, and comparisons were made between the grafts, opposing radial carpal bone, and contralateral third carpal bone. The assessment criteria included paravital staining, a modified Mankin scoring system, and biochemical analyses for collagen type, total collagen content, and sulfated glycosaminoglycan concentration.

Results—All horses were sound 21 days' postoperatively. At 6 months, all 18 grafts were intact but somewhat soft and opaque compared with surrounding carpal cartilage. Nine months' postoperatively, the bony portions of the grafts were well integrated with the recipient sites, but 6 grafts had histologic evidence of cartilage degeneration. From biochemical analysis of grafts, there was little or no new repair tissue invading the experimental sites, but sulfated glycosaminoglycan (proteoglycan) loss from the transplanted cartilage was marked.

Conclusions—Heterotopic transfer of osteochondral grafts from the distal aspect of the lateral femoral trochlea to the third carpal bone is feasible with minor modifications of human mosaic arthroplasty instruments. The bony portion of the osteochondral grafts was quickly remodeled to provide subchondral support to the transplanted articular cartilage. The loss of proteoglycan from the transplanted cartilage indicates that the grafts might have been injured during harvesting or insertion, or, more likely, did not remodel to meet the demands of a new biomechanical environment.

Clinical Relevance—These findings suggest that arthroscopic resurfacing of focal osteoarticular defects will not be successful in the long term unless donor and recipient sites can be matched with respect to cartilage thickness, biochemical constituents, and physical properties. Mosaic arthroplasty may be indicated in selected cases in which no other options exist to create a confluent cartilage‐covered surface.
Canine Pubic Symphysiodesis: Investigation of Electrocautery Dose Response by Histologic Examination and Temperature Measurement
Authors: Patricelli Alison J. , Dueland R. Tass , Lu Yan , Fialkowski James , Mathews Kyle G.
Published: August 2002

Objectives—To determine thermal necrosis zone and the maximal temperature achieved with various electrocautery doses applied to the pubic symphysis of immature dogs, and to establish the minimal electrocautery dose needed to affect thermal necrosis of the germinal chondrocytes of the immature canine pubis.

Study Design—A randomized, controlled, prospective study.

Animals—Twelve puppies, 15 to 17 weeks of age.

Methods—Each treated puppy was randomly selected to receive 3 of 33 possible doses of electrical current applied at uniform intervals along the pelvic symphysis. Three treatment sites were sham‐operated controls. All treatment zones were biopsied 7 days after application of electrocautery. Confocal laser microscopy with calcein green and ethidium homodimer red stains were used to determine cell type and viability within treatment and control zones. The physeal diameter and thermal necrosis zone were measured. Thermal necrosis zone and dose, and temperature and dose were compared using regression analysis. Prediction equation analysis was used to establish dose recommendations.

Results—Doses of 40 W produced a highly significant linear relationship (R2= .88,P< .01) with thermal necrosis zone, and a significant linear relationship (R2= .76,P< .02) with maximal temperature.

Conclusions—The thermal necrosis zone within the pelvic symphysis and maximal temperature achieved can be reliably predicted using electrocautery doses of 40 W. For application of electrocautery to induce pubic symphysiodesis, doses should be chosen based on measured or estimated physeal size. Using prediction equation analysis, the surgeon can plan mean thermal necrosis zone with acceptable variance.

Clinical Relevance—Unipolar needle electrocautery can be used to reliably achieve symphyseal necrosis. Prediction equation analysis can be used to determine 40‐W doses.
Analgesic Effect of the Transdermal Fentanyl Patch During and After Feline Ovariohysterectomy
Authors: Glerum Leigh E. , Egger Christine M. , Allen Sheila W. , Haag Michelle
Published: August 2002

Objective—To evaluate the efficacy of the transdermal fentanyl patch in relieving perioperative pain and stress associated with ovariohysterectomy in cats.

Study Design—Prospective laboratory trial.

Animals—Twenty‐four female, purpose‐bred cats.

Methods—Each cat was randomly assigned to groups 1–3. Group 1 received a 25‐μg/h transdermal fentanyl patch only. Group 2 received the patch and anesthesia. Group 3 received anesthesia only. Patches were left in place for 72 hours. Rectal temperature, heart rate, respiratory rate, indirect blood pressure, blood glucose, serum cortisol concentration, plasma fentanyl concentration, pain score, and excitement/sedation score were monitored at prescribed intervals over an 81‐hour period. Cats from groups 1–3 were reassigned to groups 4 and 5. Group 4 received the patch, anesthesia, and an ovariohysterectomy. Group 5 received anesthesia and an ovariohysterectomy only. The study period and monitored parameters were the same as for groups 1–3.

Results—Serum cortisol concentrations were significantly lower in group 4 than group 5 during the surgical and early postsurgical time periods. A similar effect was noted in blood glucose concentrations during the surgical period. Rectal temperature was significantly higher in group 2 when comparing all anesthetized groups during the early postsurgical period. Pain scores were significantly higher in groups 4 and 5 than in groups 2 and 3 during the early postsurgical period. There was no significant difference in pain scores between groups 4 and 5 during this period, however.

Conclusions—The transdermal fentanyl patch affects biochemical markers of perioperative pain and stress associated with ovariohysterectomy in cats, attenuating rises in serum cortisol and blood glucose concentrations during the surgical and early postsurgical periods.

Clinical Relevance—The transdermal fentanyl patch is effective in alleviating perioperative pain and stress associated with ovariohysterectomy in cats as evidenced by attenuated rises in cortisol and blood glucose concentrations in cats that were operated on and treated with the patch.
Sensitivity of Radiographic Evaluation of Radio‐Ulnar Incongruence in the Dog In Vitro
Authors: Mason David R. , Schulz Kurt S. , Samii Valerie F. , Fujita Yukihiro , Hornof William J. , Herrgesell Eric J. , Long Craig D. , Morgan Joe P. , Kass Phillip H.
Published: August 2002

Objective—To determine the sensitivity and specificity of radiographic evaluation of radio‐ulnar incongruence in canine elbow joints in vitro.

Study design—Radiographic evaluation of induced radio‐ulnar incongruence in canine cadaveric forelimbs by radiologists blinded to study design.

Sample population—Six cadaveric canine left forelimbs.

Methods—Extended lateral, 90° flexed lateral, and cranio‐caudal projections were taken of the elbow joint of six cadaveric canine forelimbs. A four‐pin, type I external skeletal fixator (ESF) with a linear motor side bar was attached to the medial aspect of the radius, and a 2‐cm segment of bone was removed from the mid‐diaphysis. A 3.5‐mm cortical bone screw placed from the medial to lateral styloid processes prevented relative movement between the distal radius and ulna during radial shortening. The ESF was used to progressively shorten the radius in increments of 0.5 mm to a total of 4 mm. The three radiographic projections were repeated after each incremental change of length. After the study, each elbow joint was disarticulated to confirm the presence of a step defect. The original radiographs and three copies were randomized and then evaluated by four radiologists blinded to the study design. Radiologists were asked to evaluate whether the joint was normal or abnormal and if there was evidence of radio‐ulnar incongruence. The ability of each radiologist to correctly identify congruent elbows (specificity) and incongruent elbows (sensitivity) was calculated.

Results—The median specificity was 86% using the lateral projection and 82% using the cranio‐caudal projection. The median sensitivities using the lateral and cranio‐caudal radiographic projections were 78% and 79%, respectively. The degree of radial shortening required for individual radiologists to achieve a sensitivity of 90% ranged from 1.5 mm to greater than 4 mm.

Clinical relevance—Standard radiographic evaluation for radio‐ulnar incongruence in the dog may be associated with relatively poor sensitivity and specificity. Invasive surgical procedures and screening programs that rely on radiographic diagnosis of radio‐ulnar incongruence should be discouraged until a more reliable method of diagnosis of this type of elbow joint incongruence is available.
Temporal Localization of Immunoreactive Transforming Growth Factor β1 in Normal Equine Skin and in Full‐Thickness Dermal Wounds
Authors: Theoret Christine L. , Barber Spencer M. , Gordon John R.
Published: August 2002

Objective—To describe the localization of immunoreactive transforming growth factor (TGF)‐β1 in both normal skin and full‐thickness dermal wounds of the limb and the thorax of the horse.

Study design—Six full‐thickness excisional wounds were created on the lateral aspect of one metacarpal region and on the midthoracic area of each horse. Sequentially collected tissue specimens from wound margins were assessed for TGF‐β1 expression by immunohistochemistry.

Animals—Four horses (2 to 4 years of age).

Methods—A neutralizing monoclonal anti‐human TGF‐β1 antibody was used to detect the spatial expression of TGF‐β1 protein by immunohistochemical localization in biopsies obtained before wounding and at 12 and 24 hours, and 5, 10, and 14 days.

Results—No differences in localization of immunoreactive TGF‐β1 were detected between limb and thorax, for either intact skin or wounds. Unwounded epidermis stained moderately for TGF‐β1 protein throughout all layers, whereas the dermis was relatively devoid of immunoreactivity. During the acute stage of repair, migrating epithelium lost its stain, whereas cells of epidermal appendages remained strongly immunoreactive. The epithelium recovered its TGF‐β1 immunoreactivity during wound remodeling, although cells of the stratum corneum remained negative. Macrophages of the inflammatory exudate had positive cytoplasmic staining that diminished with time. Immunoreactivity of granulation tissue fibroblasts was evident early on and increased throughout the repair process.

Conclusions—TGF‐β1 is constitutively expressed in normal, unwounded equine epithelium. Its expression is upregulated within the skin on injury and is associated with the cells involved in wound repair.

Clinical relevance—A more precise understanding of the temporal and spatial expression of TGF‐β1 during wound repair in horses should provide the groundwork for possible future manipulations of both normal and aberrant tissue repair.
A Biomechanical Comparison of Equine Third Metacarpal Condylar Bone Fragment Compression and Screw Pushout Strength between Headless Tapered Variable Pitch and AO Cortical Bone Screws
Authors: Galuppo Larry D. , Stover Susan M. , Jensen David G.
Published: August 2002

Objectives—To compare bone fragment compression and the mechanical pushout strength and stiffness of 6.5‐mm Acutrak Plus (AP) and 4.5‐mm AO cortical (AO) bone screws after stabilization of a simulated equine third metacarpal (MC3) bone complete lateral condylar fracture.

Study design—In vitro biomechanical paired study of screw insertion variables, bone fragment compression, and screw pushout tests using a bone screw stabilized simulated lateral condylar fracture model.

Sample population—Six pairs of cadaveric equine MC3s.

Methods—Metacarpi were placed in a fixture and centered on a biaxial load cell in a materials testing system to measure torque, compressive force, and time for drilling, tapping, and screw insertion. Fragment compression was measured with a pressure‐sensing device placed between the simulated fracture fragments during screw insertion for fragment stabilization. Subsequently, screws were pushed out of the stabilized bone fragments in a single cycle to failure. A pairedttest was used to assess differences between site preparation, screw insertion, fragment compression, and screw pushout variables, with significance set atP< .05.

Results—Measured drilling variables were comparable for AO and AP specimens. However, the AP tap had significantly greater insertion torque and force. Mean maximum screw insertion torque was significantly greater for AO screws. For fragment compression, AP screws generated 65% and 44% of the compressive pressure and force, respectively, of AO screws. AP screws tended to have higher overall pushout strength. Pushout stiffness was similar between both screw types.

Conclusion—The 6.5‐mm tapered AP screw generated less interfragmentary compressive pressure and force but had similar pushout stiffness. Evaluation of failure patterns demonstrated that AP screws had greater pushout strength compared with 4.5‐mm AO screws for fixation of a simulated complete lateral condylar fracture.

Clinical relevance—The 6.5‐mm tapered AP screw should provide ample holding strength but would provide less interfragmentary compression than 4.5‐mm AO screws for repair of complete lateral condylar fractures in horses.
Recombinant Equine Growth Hormone does not Affect the In Vitro Biomechanical Properties of Equine Superficial Digital Flexor Tendon
Authors: Dowling Bradley A. , Dart Andrew J. , Hodgson David R. , Rose Reuben J. , Walsh William R.
Published: August 2002

Objective—To evaluate the effect of recombinant equine growth hormone (rEGH) on the in vitro biomechanical properties of normal adult equine superficial digital flexor tendon (SDFT).

Study design—Completely randomized design.

Sample population—Nine Standardbred horses, 6 to 9 years of age with ultrasonographically normal forelimb SDFT.

Methods—Six horses were administered intramuscular (IM) rEGH at 10 μg/kg/day for 1 week, and then 20 μg/kg/day for another 5 weeks; 3 horses (control subjects) were administered an equivalent daily volume of sterile water IM. Horses were killed at the end of the 6‐week treatment period, and both forelimb SDFT were harvested and stored at −70°C. In vitro biomechanical testing was performed under uniaxial tension. Results were analyzed using a general linear model of analysis of variance; significance was set atP < .05.

Results—There were no differences in cross‐sectional area, maximal load at failure, yield load, ultimate and yield tensile strain, ultimate and yield tensile stress, or stiffness between tendons from control and treated horses.

Conclusions—Administration of rEGH to adult Standardbred horses for 6 weeks had no detectable effect on the in vitro biomechanical properties of normal SDFT.

Clinical relevance—Administration of rEGH does not modulate the in vitro biomechanical properties of SDFT from adult Standardbred horses.
The Use of Porcine Small Intestinal Submucosa as a Biomaterial for Perineal Herniorrhaphy in the Dog
Authors: Stoll Melissa R. , Cook James L. , Pope Eric R. , Carson William L. , Kreeger John M.
Published: August 2002

Objectives—To develop an in vivo perineal hernia model, to develop a technique for using small intestinal submucosa (SIS) in perineal hernia repair, to further elucidate the biological behavior of SIS, and to compare SIS herniorrhaphy with the internal obturator muscle transposition (IOT) technique.

Study design—Prospective evaluation comparing SIS herniorrhaphy with IOT.

Animals—Twelve adult castrated male, large‐breed dogs.

Methods—All dogs had bilateral pelvic diaphragm defects created by complete excision of the levator ani muscle. Each dog had one side repaired using SIS and the other by IOT. Pain and inflammation were subjectively scored. Dogs were killed 2 weeks (n =4), 12 weeks (n =4), or 16 weeks (n =4) after surgery. Each pelvic diaphragm was biomechanically tested to failure. The pelvic diaphragms from 2 normal dogs (n =4sides) were also biomechanically tested. Failure site, maximum pressure, displacement at failure, and initial linear stiffness values were determined. Histologic assessment was performed. Statistical analysis was performed with significance set atP< .05

Results—No significant postoperative complications were noted. There were no significant differences in maximum pressure to failure, displacement, or stiffness when comparing normal, SIS, and IOT at any time point. The SIS group had significantly less displacement (P=.004) at 2 weeks than at weeks 12 or 16. For all herniorrhaphy techniques, the failure site was central (n =22) or at the suture line (n =2). At 2 weeks, histologic evaluation of tissues from the IOT group showed inflammation, mineralization, and necrosis, which were not present in tissues from the SIS group. Histologic examination at 12 and 16 weeks showed no microscopic differences in cell population or tissue characteristics between the IOT and SIS groups.

Conclusions—SIS herniorrhaphy was successfully performed in this in vivo model of perineal hernia in the dog.

Clinical relevance—This study suggests that SIS can be used as a primary means of repair, as augmentation when the internal obturator muscle is thin and friable, or as a salvage procedure in cases of recurrence in dogs with perineal hernia.
The Effects of Femur and Implant Position on the Radiographic Assessment of Total Hip Femoral Implants in Dogs
Authors: Jehn Carl T. , Manley Paul A.
Published: August 2002

Objective—To determine the effect of femur positioning and femoral implant placement on the radiographic assessment of total hip femoral implants in dogs.

Study design—Cadaveric study.

Animals—Five canine femurs.

Methods—Five canine femurs were fitted with total hip implants, in predetermined locations, postmortem. Each femur was moved through a defined range of motion and radiographed at specific intervals. Radiographs were then digitized, and implant position was measured using previously described methods. Regression analysis was conducted to determine whether varied femoral position resulted in a consistent (linear) pattern of change in the value of each particular measurement.

Results—Change in the position of the femur relative to the film cassette caused significant variation in the perceived position of the implant. The placement of the implant within the femur determined which measurements were affected and to what degree.

Conclusions—The information obtained from standard clinical radiographs and conventional methods of quantitative analysis does not consistently provide an accurate assessment of the placement of the femoral implant within the femoral canal. Such data cannot be used to correlate implant position with implant failure.
Facets of cholesterol crystallization in human bile
Authors: G M Murphy
Published: August 2002

In Europe some 10% of men and some 20% of women have gallstones. In most cases these stones remain silent and do not present any problems. However, about one in five of the people with gallstones do develop symptoms which necessitate treatment. Gallstones may be classified according to their composition as being cholesterol rich, mixed or pigment. Cholesterol gallstones are the most common. About 70% of gallstones in English patients are cholesterol rich. This review of studies of the formation of gallstones focuses on the process of cholesterol crystallization from bile. In bile, cholesterol is present in mixed micelles and vesicles, and one of the major problems in this field has been the isolation of these biliary cholesterol complexes without disruption, or modification, of their content. Calcium is a major component of cholesterol gallstones and is considered to play an important role in vesicle aggregation which is believed to be an important prerequisite to cholesterol crystal deposition. Both pronucleation and antinucleation factors are found in gallbladder bile. High protein concentrations and high pH have also been implicated.
Voltage-current density characteristics of noble gas mixture discharges in the cathode region
Authors: Z Donko  , K Rozsa  , M Janossy
Published: August 2002

Voltage-current density (V-j) characteristics were studied in the cathode region of noble gas mixture glow discharges. Measurements were carried out in He-X (X=Ne,Ar,Kr,Xe) mixtures in plane cathode and hollow cathode arrangements. The partial pressure of the admixed gas was at a maximum of 2% of the total pressure. It was found that at constant voltage the current density increased by mixing Ar to He, while it decreased when Ne, Kr or Xe were added. Above a certain partial pressure value the current density was found to increase again in the case of Ne and Kr admixtures. In He-Xe it decreased, however, in the whole range investigated. These observations are explained, taking into account ionization processes and the differences in secondary electron emission coefficients.
Low-pressure gas discharge modelling
Authors: G G Lister
Published: August 2002

Low-pressure gas discharge modeling is reviewed, both from a historical perspective and for current industrial applications. An overview of the basic mathematical and physical models used to describe low-pressure discharges is given, together with a summary of the most common numerical techniques which have been adopted. Modelling of the DC glow discharge and discharges maintained by high-frequency (RF and microwave) electromagnetic fields is reviewed with illustrations of the validity of these models in predicting discharge properties and explaining and interpreting experimental results.
Optogalvanic study of a negative ion plasma in a hollow cathode discharge in oxygen
Authors: H Amemiya  , K Ogawa  , T Suzuki  , M Endou
Published: August 2002

The properties of a negative ion plasma in a hollow cathode discharge have been investigated in oxygen using optogalvanic and probe methods. In the former method, the laser photodetachment technique is applied, and data which support the existence of negative ions are obtained by using CW and pulsed lasers. Appreciable amounts of negative ions are generated between 40 and 150 Pa and at relatively lower discharge currents. It is found that O-or O3-are more dominant at medium currents while O2-is more dominant at lower currents. At high currents, negative ions disappear. The electron energy distribution is depleted in the low-energy region below 1 eV. At higher energies, the energy distribution is almost Maxwellian with an electron temperature of 2.5-3.0 eV. The electron density ranges from 109to 1010cm-3and the ratio of the negative to positive ion density is 0.2-0.6 depending on the pressure and the current.
A dialysis technique for determining aggregate concentrations in crystallizing protein solutions
Authors: L J Wilson  , L D Adcock  , M L Pusey
Published: August 2002

The authors have adapted a dialysis technique which provides aggregate concentrations of protein molecules in solutions which lead to crystal growth. In dialysis, the flux across a semipermeable membrane is directly proportional to the concentration of the diffusible solute inside the bag provided that the solute concentration in the bulk solution is infinitely dilute. Using membranes of varying porosity, the concentrations of different size solutes can be measured by measuring the flux rate across the membrane. They have used this technique to independently measure the concentrations of monomers, dimers, trimers and higher aggregates of lysozyme in both 1% NaCl and 3% NaCl (0.1 M NaAc, pH4) using 25 K and 50 K molecular weight cut-off membranes. They compare these concentration profiles with (110) face growth rate data under the same conditions.
A general theory of relativistic asymptotic aberrations of a system of combined focusing-deflection sub-systems
Authors: Yu Li
Published: August 2002

In this paper, a general theory of the relativistic asymptotic third-order geometric and first-order chromatic aberrations of a system of combined electrostatic-magnetostatic focusing-deflection sub-systems has been presented, in which relativistic asymptotic aberrations of position and slope of the sub-system, and addition formulae for these asymptotic aberrations of two successive subsystems have been derived. All their aberration coefficients contain no derivative higher than second order. The divergence in Hawkes' theory of asymptotic aberrations has been thoroughly voided. The limitation of equality of object- and image-side asymptotic focal lengths in Hawkes' theory has been erased.
An investigation of the collisionless discharge in the presence of an electron beam
Authors: N Jelic  , M Cercek  , M Stanojevic  , T Gyergyek
Published: August 2002

The properties of a plane collisionless plasma are investigated by using the Tonks-Langmuir model with the assumption of an electron beam in addition to Maxwellian bulk electrons. The case of very energetic beam electrons, as well as the case when the beam electrons acquire the greatest part of their energy in the sheath and the presheath regions, are considered under the condition that the discharge is terminated by a floating wall. In the case of a very energetic beam the plasma can be terminated by a double layer appearing close to the wall or, provided the beam density is high enough with respect to the bulk electron density, by a quasineutral double layer like structure. In the case of a beam of a small initial energy, however, the double layer and double layer like structures appear far from the wall even for very small beam densities. The last result opens a question about the relevance of the initial assumptions made on the electron velocity distribution in non-energetic and very energetic beams. The plasma flow to the boundary was calculated for the cases when the initial assumptions may be regarded as quite regular, and the results were compared with those ones obtained under the assumption of monoenergetic ions at the plasma-sheath boundary.
Ion drag and plasma-induced thermophoresis on particles in radiofrequency glow discharges
Authors: J Perrin  , P Molinas-Mata  , P Belenguer
Published: August 2002

A comparison is made of the forces governing the transport of negatively charged particles electrostatically suspended in the plasma of a symmetric parallel-plate radiofrequency glow discharge with isothermal walls. The two forces driving the particles symmetrically from the plasma centreline to the sheath edges are the ion drag force and the plasma-induced thermophoresis due to the thermal gradient appearing in the gas heated by plasma power dissipation. A general expression of the ion drag force as a function of the ratio of the ion drift velocity and thermal velocity is obtained by a proper integration over the ion energy distribution using the analytical expression for the ion orbital momentum transfer cross section derived by Kilgore et al. (J. Appl. Phys. 73 7195 (1993)). The ion drag force is then compared with the plasma-induced thermophoresis on submicrometre-size particles in well-characterized experimental discharge conditions in Ar. It appears that ion drag is usually larger than thermophoresis on an isolated particle in a pristine discharge. However, thermophoresis always dominates over ion drag in dusty discharges where plasma-particle and particle-particle interactions result in a drastic reduction of the ion drift velocity through the plasma bulk.
Optical properties of AgGaSe2 polycrystalline films prepared by flash evaporation
Authors: H S Soliman
Published: August 2002

Structural studies on AgGaSe2 films prepared in vacuum of 10-4 Pa onto glass or quartz substrates by a flash evaporation technique and annealed at 573 K for 2 h show that these films were polycrystalline and exhibited tetragonal chalcopyrite structure with a strong (112) orientation with a=0.599 nm, c=1.089 nm and (c/a)=1.816. The optical constants (the refractive index n, the absorption index k and the absorption coefficient varies as ) of polycrystalline AgGaSe2 films were determined from spectrophotometric measurements of the transmittance and reflectance carried out at normal incidence in the wavelength range 500-2000 nm. Graphical representations of surface and volume energy loss functions as well as the real optical conductivity as a function of photon energy show the existence of three possible optical transitions corresponding to 1.79, 1.95 and 2.2 eV respectively.
Early experimental proofs of the dynamical theory
Authors: G Hildebrandt
Published: August 2002

The early experimental proofs of the dynamical theory can roughly be subdivided into the periods 1914-35, 1935-40 and 1940-65. Experiments mostly performed with calcite crystals in the Bragg case in the first of these periods confirmed Darwin's theory from 1914. Later observations, however, such as the Renninger effect, Pendellosung fringes and others, needed Ewald's 1917 theory for their interpretation, founding a second period, After 1940 Borrmann's experiments and their interaction with von Laue's expansions of his 1931 form of the theory initiated a third period of deeper understanding of the properties of Ewald's wavefields, finally smoothing the way to a true 'crystal optics of X-rays' with the help of artificially grown crystals of high perfection.
Determination of fibre-resin interface strength in fibre-reinforced plastics using the acoustic emission technique
Authors: E U Okoroafor  , R Hill
Published: August 2002

The acoustic emission (AE) technique has been employed in a new way, to deduce information regarding the level of adhesion and the strength of the bond between fibres and the matrix materials used in composite manufacture using a transverse sample based on fibre bundles. When unidirectional composites of E-glass fibres/polyester and Kevlar-49 fibres/polyester respectively were subjected to transverse tension, the AE events associated with fibre-matrix interfacial failure started and eventually saturated at low strains in the materials containing Kevlar-49 when compared with those containing E-glass. This clearly indicates that E-glass adheres far better to polyester than does Kevlar-49 and, from stress measurements, the E-glass/polyester bond is stronger. These results are compared and discussed with respect to those from single-fibre composite (SFC) tests which gave similar interfacial shear strength values for the E-glass/polyester and Kevlar-49/polyester interfaces and which may be interpreted in terms of similar levels of adhesion. Further experimentation, with composites whose fibres were surface-treated prior to composite manufacture, showed that the method is a simple and convenient means of monitoring adhesion and interfacial bond strength in fibre-reinforced plastics. Acoustic emission has proved a useful technique in casting new light on the quality (and reality) of surface adhesion in composite material systems and has provided a new method for measuring the strength of resin/fibre surface adhesion in tension.
A study on the coercivity and the magnetic anisotropy of the lithium ferrite nanocrystallite
Authors: Hua Yang  , Zichen Wang  , Lizhu Song  , Muyu Zhao  , Jianping Wang  , Helie Luo
Published: August 2002

Lithium ferritenanocrystallites ranging from several nanometres to several hundreds of nanometres in size have been prepared by the polyethylene glycol gel method. These nanocrystallites were identified as pure lithium ferrite by x-ray diffraction analysis. Their magnetization and de-magnetization were measured by using a vibrating sample magnetometer at different temperatures. The specific saturation magnetization and the coercivities change with the diameter of these nanocrystallites and with temperature. The effective magnetic anisotropy constantsof these samples were deduced by using the law of approach to saturation. It is found that thevalue of a lithium ferrite nanocrystallite of diameter 9.1 nm is about ten times greater than the magnetocrystalline anisotropy constantof bulk lithium ferrite. The coercivities of these nanocrystallites at different temperatures were calculated by using the mixed coercivity model. The calculated coercivity results are consistent with the experimental ones.
The spatial hole burning effect in gain-guided vertical-cavity surface-emitting lasers
Authors: Jacek Wilk  , Robert P Sarzala  , Wlodzimierz Nakwaski
Published: August 2002

Comprehensive, three-dimensional, thermal - electrical - optical self-consistent simulation of gain-guided vertical-cavity surface-emitting lasers (VCSELs) is used to study the mutual interaction in a VCSEL resonator between the carrier-concentration distribution and the laser intensity profile, called usually the spatial hole burning (SHB) effect. In the simulation, the beam-propagation method (BPM) is applied to investigate a VCSEL optical field whereas finite-element and finite-difference techniques allow modelling of heat-flux, current-spreading and carrier diffusion phenomena. BPM turns out to be very efficient in analysing laser optical fields. The SHB effect is found to influence considerably both carrier-concentration and intensity profiles in VCSEL active regions, therefore it is proved to play an important role in many physical processes (thermal, electrical and optical phenomena) occurring during operation of a VCSEL.
Magnetism of thin epitaxial Cr films in sandwich structures and superlattices
Authors: Hartmut Zabel  , Patrick Bödeker  , Andreas Schreyer
Published: August 2002

The spin density wave (SDW) magnetism of thin epitaxial Cr films has recently become the focus of interest because of its mediating role in exchange coupled superlattices. While the incommensurate SDW and the Néel temperature,, are well established for bulk Cr, the question arises of how these properties are altered in thin films and superlattices with ferromagnetic boundary layers. We review here recent synchrotron and neutron scattering experiments to probe the commensurate and incommensurate SDWs in epitaxial Cr(100) layers and the phase diagrams which result from these measurements as a function of film thickness and temperature. Finally, we link the antiferromagnetic spin structure of Cr to the Fe layer magnetization vectors in exchange coupledsuperlattices, which provides a deeper insight for the cause of non-collinear magnetic ordering in these artificial superlattices.
New tomographic approach for deconvolution of ion velocity and temperature profiles in a plasma centrifuge
Authors: N P Poluektov  , N P Efremov
Published: August 2002

Tomographic equations for the velocity and temperature of heavy particles in plasma have been derived using the relations of the velocity distributions with the Doppler shift and broadening of the spectral lines. These equations are correct for non-Maxwellian velocity distributions and for arbitrary plasma flow. This approach was used for the computation of ion velocity and temperature radial distributions from the spectroscopic data in a highly ionized plasma centrifuge. Separation factors of 15 for Ar-Kr and 22 for Ar-Xe mixtures with a density ofare obtained.
Two-dimensional analysis of the nuclear relaxation function in the time
domain: the program CracSpin
Authors: W P Weglarz  , H Haranczyk
Published: August 2002

The analysis of the NMR relaxation function for
microheterogenous systems usually starts with the decomposition of the
relaxation function to discrete components, or finding a continuous
distribution of the components. Several approaches can be applied to do
this: linear least-squares fitting, non-linear least-squares fitting or
inversion of the data, based on the Laplace transformation. The
spin-grouping technique - a correlated analysis of the spin-lattice
relaxation function (recovery or decay) and spin-spin relaxation decay
(free induction decay or Carr-Purcell decay) - usually enables a
decomposition of relaxation data into a proper set of discrete components.
In our paper, we present CracSpin, a program for one and/or
two-dimensional analysis of the relaxation function in the time domain. It
uses Marquardt's algorithm for non-linear least-squares fitting. The
results of analyses of simulated data containing discrete as well as
continuous distributions of the components are shown. CracSpin resolves
the components of FID even if the ratio of their relaxation times is as
small as 2, for comparable component magnitudes (at least about 10% of
total signal) and for signal-to-noise ratio (S/N) >100. If the ratio of
component relaxation times is higher than ~3, the decomposition is
satisfactory for S/N >10, even for a component magnitude of about 1%.
The noise level is defined here as equal to the three standard deviations
of the normal distribution. The two-dimensional analysis significantly
improves the quality of the multicomponent decomposition, for composed
decays or in the case of close values of the relaxation time of the
components. The representative examples of the analysis, starting from
spin-lattice relaxation curves, as well as from spin-spin relaxation
curves, are presented and discussed.
Multipole
theory solution of two-dimensional unbounded eddy current
problems
Authors: Qinhong Zheng  , Jidong Yi  , Fuyao Xie  , Li Ma
Published: August 2002

A new approach, the multipole theory (MT) method, is presented for the computation of two-dimensional (2D) unbounded eddy current problems. The essential concept is to represent the solution of the governing partial differential equation by the generalized MT formulae of the 2D Helmholtz equation and the 2D Laplace equation. The least squares method reduces the problem to the solution of a set of linear equations. Ampere's law, as an additional constraint, is used to guarantee that the total net current is not changed due to the induced fields, and the radiation boundary conditions are satisfied. The eddy current problems of elliptic conductor, square conductor and a pair of circular conductors are considered as examples. The results obtained by the MT method are compared with experimental results and previously published work. It is shown that the MT method is an effective approach for computation of 2D unbounded eddy current problems.
Time
evolution of pulsed supersonic jets of argon clusters
Authors: A V Malakhovskii
Published: August 2002

The correlation between cluster decomposition and the structure of pulsed supersonic jets of argon clusters is analysed. The longitudinal and transverse space structures of short supersonic pulses (
0.5 ms) of argon clusters have been studied far from the skimmer, by a movable mass spectrometer and near the skimmer, by an electron impact ionizer, depending on the stagnation pressure. It has been found that the pulses consist of two distinct fractions of clusters, light and heavy, which are also differently localized in space. The heavy fraction is located inside the pulses and the light fraction is mainly found in the outlying area of the pulses. It has been shown that neutral clusters reveal instability for a long period of time (~0.6 ms) after condensation. This instability results in additional divergence of the cluster beam. Therefore, the change of the cluster beam cross section as a function of the pressure correlates with the corresponding change in the cluster instability.
High electric field measurement of dielectric constant and losses of ferroelectric ceramics
Authors: J E García  , R Pérez  , A Albareda
Published: August 2002

Nonlinear behaviour of power piezoceramic materials has to be studied under strong electric fields. A bridge designed for measuring it at low frequency is described. It consists basically of a capacitance comparison bridge that can be used in two different modes: balanced and unbalanced. The nonlinear electric displacement is split into dissipative and nondissipative terms. Dielectric constant is computed from the last term and related to the instantaneous field. The behaviour of soft and hard PZT ceramic materials has been tested according to this model. In both materials, the dielectric constant not only depends on the instantaneous value of the field but also on its amplitude. While the dependence of the real and imaginary parts of the dielectric constant in soft ceramics is large and practically linear to the field amplitude, in hard PZT it is low and nearly quadratic. The rate between both parts depends on the type of ceramic. Dielectric constant can be divided into two terms. One term is allied to the irreversible motion of domain walls, while the other is related to reversible motion. Balanced and unbalanced modes have been tested for both materials, and results are coherent. Accuracy and limitations of the method are discussed.
Transient high
concentrations of chain anions in hydrating
cement - indications from proton spin relaxation measurements
Authors: N Nestle  , C Zimmermann  , M Dakkouri  , J Kärger
Published: August 2002

Studies of the dynamics of liquid water in the pores of hydrating cement
materials were performed by means of various nuclear magnetic resonance
techniques, such as spin-echo T
2 relaxometry, echo-detected
saturation-recovery T
1 relaxometry and pulsed field gradient
diffusometry. While the diffusion coefficients and the transverse relaxation
times were found to decrease monotonically with hydration time, the
longitudinal relaxation time exhibits a transient minimum during the onset
of the acceleration phase. Earlier explanations of the minimum can
be ruled out on the basis of our experimental data and a new one is
suggested. The findings are corroborated by observations in cement pastes
with added fine particles.
Finite-size effects in fine particles: magnetic and transport properties
Authors: Xavier Batlle  , Amílcar Labarta
Published: August 2002

Some of the most relevant finite-size and surface effects in the magnetic and transport properties of magnetic fine particles and granular solids are reviewed. The stability of the particle magnetization, superparamagnetic regime and the magnetic relaxation are discussed. New phenomena appearing due to interparticle interactions, such as the collective state and non-equilibrium dynamics, are presented. Surface anisotropy and disorder, spin-wave excitations, as well as the enhancements of the coercive field and particle magnetization are also reviewed. The competition of surface and finite-size effects to settle the magnetic behaviour is addressed. Finally, two of the most relevant phenomena in the transport properties of granular solids are summarized namely, giant magnetoresistance in granular heterogeneous alloys and Coulomb gap in insulating granular solids.
Space and Time Coherence of Acoustic Field in Shallow Water
Authors: Guo Liang-Hao  , Gong Zai-Xiao  , Wu Li-Xin
Published: August 2002

New experimental measurements of signal coherence in shallow water are
presented. For signals with low frequencies of about 500 Hz in
iso-velocity shallow water with a silt-sand bottom and a water depth of about
45 m, the vertical coherence has no distinct depth dependence at ranges of
18.5, 55.5 and 92.5 km, but it has obvious range dependence. The horizontal
coherence lengths are all greater than 40 wavelengths, and the time
coherence lengths are all greater than 510 s at these ranges.
These experimental results show that a low-frequency acoustic
field has strong spatial coherence and temporal stability in iso-velocity
shallow water.
Isostructural Transition of MgB2Under High Pressure
Authors: Sun Li-Ling  , T. Kikegawa  , Wu Qi  , Zhan Zai-Ji  , Wang Wen-Kui
Published: August 2002

The high-pressure behaviour of the superconductor MgB2with a hexagonal structure has been investigated by thein situsynchrotron radiation x-ray diffraction method under pressures up to 42.2 GPa in a diamond anvil cell. An abrupt decrease of about 7% in the unit cell volume of this material occurs in the pressure range of 26.3-30.2 GPa. A split of the Raman spectrum was also observed. The jump of the compression curve and Raman spectrum are ascribed to an isostructural transition in MgB2at a pressure of 30.2 GPa.
Global study of a family of cubic Liénard equations
Authors: Alexander I Khibnik  , Bernd Krauskopf  , Christiane Rousseau
Published: August 2002

We derive the global bifurcation diagram of a three-parameter family of cubic Liénard systems. This family seems to have a universal character in that its bifurcation diagram (or parts of it) appears in many models from applications for which a combination of hysteretic and self-oscillatory behaviour is essential. The family emerges as a partial unfolding of a doubly degenerate Bogdanov-Takens point, that is, of the codimension-four singularity with nilpotent linear part and no quadratic terms in the normal form. We give a new presentation of a local four-parameter bifurcation diagram which is a candidate for the universal unfolding of this singularity.
Asymmetry parameters in two-photon detachment of H−below 1 eV
Authors: I Sánchez  , H Bachau  , F Martín
Published: August 2002

We present theoretical calculations for two-photon detachment rates and asymmetry parameters of H−for energies below 1 eV. The calculated asymmetry parameters compare very well with values determined in a recent experimental work. This is the first time that this kind of comparison has been made for H−, which reinforces the predictive value of previous theoretical works on the two-photon detachment of H−for which experiments are still lacking.
Two-photon double ionization of He and H−
Authors: M S Pindzola  , F Robicheaux
Published: August 2002

Two-photon absorption processes resulting in two-electron ionization of He and H−are calculated using a time-dependent close-coupling expansion on a two-dimensional radial lattice. The ground state atom or ion is subjected to a 10-cycle pulse of linearly polarized light with peak intensities ranging from 1013to 1016W cm−2. Probabilities are calculated for one-photon single ionization, two-photon single ionization and two-photon double ionization. The ratio of non-sequential double ionization to single ionization following two-photon absorption is found to be somewhat larger than the similar ratio following one-photon absorption.
The credibility of information sources in West Germany after the Chernobyl disaster
Authors: Peters Hans Peter
Published: August 2002

In West Germany the `information disaster' after Chernobyl offered an opportunity to study the credibility of different information sources. A representative survey conducted in May 1987 of the West German population showed that on average the Federal Government—although heavily criticized because of its information policy and risk management—was rated most credible while the nuclear industry was judged least credible. On the whole, mean credibility ratings differed surprisingly little between sources; ratings of competence and public interest orientation varied more. These variables, interpreted as the classical credibility factors `expertise' and `trustworthiness', were important predictors of credibility. But beliefs and expectations recipients posess about individual sources also appear to influence credibility.