High-resolution x-ray scattering from epitaxial thin films of Y/Nb on Al2O3.

During the 1990s, Roger Cowley had a strong interest in the crystal and magnetic structures of rare-earth superlattices as a means to understand the rich and exotic magnetic properties of the rare-earth metals. High-quality samples can be grown by molecular beam epitaxy on sapphire substrates by first depositing a thin epitaxial layer of niobium, then a layer of yttrium or lutetium as a seed. High-resolution x-ray scattering is an excellent probe to characterise the crystal quality and was used to study the structure of the niobium layer. However, relatively little attention was paid to the seed layer. This article summarises some of the x-ray experiments performed by the Cowley group to study the structure of epitaxial [Formula: see text] niobium on [Formula: see text] sapphire, and extends the work to report some results on the structure of thin [Formula: see text] yttrium seed layers. The structure of the yttrium films is shown to have a strong dependence on the thickness of the niobium buffer, with the buffer needing to be thicker than a critical value of ∼80 [Formula: see text] for the formation of misfit dislocations at the Nb/Al2O3 interface before highly coherent Y films can be grown. Yttrium films grown on Nb buffers thinner than ∼500 [Formula: see text] show a similar two-peak line shape in [Formula: see text] scans through their specular Bragg peaks to that seen in the specular Nb Bragg peaks, with a resolution-limited feature on a broader diffuse peak. The resolution-limited feature depends on the thickness of the yttrium film, becoming weaker and having a stronger decay with increasing [Formula: see text] as the film thickness increases, while the width of the yttrium broad peak evolves as the square root of the width of the niobium Bragg peak. The data are discussed within the context of theories describing the scattering from films with misfit dislocations.

Phase transition of chemically doped uniaxial relaxor ferroelectric.

We report a neutron scattering study of the ferroelectric phase transition in Sr0.585Ce0.025Ba0.39Nb2O6 (SBN-61:Ce). We find no evidence for a soft transverse optic phonon. We do, however, observe anisotropic diffuse scattering. This scattering has inelastic and elastic contributions. In the paraelectric phase the susceptibility associated with the elastic diffuse scattering from SBN-61:Ce increases on approaching the transition temperature. In the ferroelectric phase the lineshape of the elastic scattering is consistent with the form expected for the ferroelectric domain walls. In contrast to the macroscopic observations, the scattering properties of Ce-doped crystal do not exhibit important changes with respect to those of pure Sr0.61Ba0.39Nb2O6.

Phase transition of the uniaxial disordered ferroelectric Sr(0.61)Ba(0.39)Nb(2)O(6).

We report a neutron scattering study of a ferroelectric phase transition in Sr0.61Ba0.39Nb2O6 (SBN-61). The ferroelectric polarization is along the crystallographic c-axis but the transverse acoustic branch propagating along the 〈1, 1, 0〉 direction does not show any anomaly associated with this transition. We find no evidence for a soft transverse optic phonon. We do, however, observe elastic diffuse scattering. The intensity of this scattering increases as the sample is cooled from a temperature well above the phase transition. The susceptibility associated with this diffuse scattering follows the anomaly of the dielectric permittivity of SBN-61 well. Below Tc the shape of this scattering is consistent with the scattering expected from ferroelectric domain walls. Our results suggest that despite apparent chemical disorder SBN-61 behaves as a classic order-disorder uniaxial ferroelectric with critical fluctuations in the range <10(-11) s.

Strain and tilt during epitaxial growth of highly ordered In2O3 nanorods.

Precise control over the morphology of one-dimensional (1D) nanostructures is an essential step in the effort to develop nano-devices with exotic properties. Here we demonstrate the formation of highly aligned In2O3 nanorod arrays on Y-stabilised ZrO2(110) grown by oxygen plasma assisted molecular beam epitaxy. The evolution of morphologies, strain and tilt in the In2O3 nanorods are studied by atomic force microscopy and high resolution synchrotron-based X-ray diffraction. It is shown that the preferential 1D growth is driven by minimization of the total surface and interface energies. The mismatch of ca. 1.7% between the substrate and the epilayer is accommodated by strain along the [110] direction coupled with tilting of the rods along [001] and [001] directions and contraction in the [110] direction. The present highly ordered In2O3 nanorod arrays supported on an insulating substrate are of potential interest for large-scale fabrication of nano-devices.

The structure and low-energy phonons of the nonferroelectric mixed perovskite: BaMg1/3Ta2/3O3.

The structure of BaMg(1/3)Ta(2/3)O(3) (BMT) has been studied using x-ray scattering. The phonons have been measured and the results are similar to those of other materials with a perovskite structure such as PbMg(1/3)Nb(2/3)O(3) (PMN). The acoustic and lowest energy optic branches were measured but it was not possible to measure the branches of higher energy, possibly this is because they largely consist of oxygen motions. High-resolution inelastic measurements also showed that the diffuse scattering was strictly elastic and not directly related to the phonon spectra. Diffuse scattering was observed in BMT near the (H ± 1/2, K ± 1/2, L ± 1/2) points in the Brillouin zone and these had a characteristic cube shape. This arises from ordering of the B-site ions in BMT. Additional experiments revealed the diffuse scattering in BMT similar in shape to Bragg reflections at wavevectors of the form (H ± 1/3, K ± 1/3, L ± 1/3). Such reflections were also observed by Lufaso (2004 Chem. Mater. 16 2148) from powders and suggest that this structure of BMT consists of four differently oriented domains of a trigonal structure and results from a different ordering of the B-site ions from that responsible for the scattering at the (H ± 1/2, K ± 1/2, L ± 1/2) points. The results lead us to suggest that for BMT single crystals the bulk has the properties of a cubic perovskite, whereas the surface may have quite different structure from that of the bulk. This difference resembles the behaviour of cubic relaxors like PMN and PMN doped by PbTiO(3), where significant surface effects have been reported.

Multiparticle states in the S = 1 chain system CsNiCl3.

A continuum of magnetic states has been observed by neutron scattering from the spin-1 chain compound CsNiCl3 in its disordered gapped one-dimensional phase. Results using both triple-axis and time-of-flight spectrometers show that around the antiferromagnetic point Qc = pi, the continuum lies higher in energy than the Haldane gapped excitations. At 6 K the integrated intensity of the continuum is about 12(2)% of the total spectral weight. This result is considerably larger than the 1%-3% weight predicted by the nonlinear sigma model for the three-particle continuum.

Trauma center closures: a national assessment.

A 1990 national survey of 66 closed trauma centers across 14 states was conducted to ascertain the factors that prompted closure. Data from 44 facilities, or 67% of the centers identified, indicate that inadequate financing and physician participation were commonplace. The findings support the work of other investigators and demonstrate that uncompensated care, inadequate reimbursement, high operating costs, and lack of physician support all adversely affect trauma care in both urban and suburban settings.

Blunt traumatic rupture of the heart and pericardium: a ten-year experience (1979-1989).

Blunt traumatic rupture of the heart and pericardium, rarely diagnosed preoperatively, carries a high mortality rate. From 1979 to 1989, more than 20,000 patients were admitted to a Level I trauma center. A retrospective review identified 59 patients requiring emergency surgery for this condition. Injuries resulted from vehicular accidents (68%), motorcycle crashes (10%), pedestrians being struck by vehicles (7%), falls (5%), crushing (7%), and being struck by a horse (2%) or crane (2%). Seventeen patients (29%) had isolated rupture of the pericardium; 37 (63%) had ruptures of one or more cardiac chambers. All patients had signs of life at the scene or during transportation, but only 29 (49%) had vital signs on admission: 15 with chamber injury, 12 with pericardial rupture, and two with combined injuries. Diagnosis was established by emergency thoracotomy in the 30 patients who arrived in cardiac arrest. In the remaining 29 patients, diagnosis was made by urgent thoracotomy (41%), by subxiphoid pericardial window (34%), during laparotomy (21%), or by chest radiography (3%). The overall mortality rate was 76% (45 patients), but only 52% for those with vital signs on admission. Rapid transportation and expeditious surgical treatment can save many patients with these injuries.

Seatbelt effectiveness and cost of noncompliance among drivers admitted to a trauma center.

Enactment of seatbelt legislation in Maryland presented the opportunity to compare seatbelt compliance among seriously injured drivers admitted to a Level I trauma center and to establish levels of severity, length of stay, and hospital cost differences among the study population. Fifty-five randomly selected drivers were examined from a total surgical population of 689. Seatbelt compliance rate was 41.8%, reflecting the rate in the community. Seatbelts reduced the total number of injuries by 34%, major injuries by 57%, and minor injuries by 20%. No deaths occurred among the belted group. The unbelted group had a mean Injury Severity Score two times as great as the belted group and were hospitalized 1.6 times longer at double the cost. Major injuries to the face, chest, and pelvic regions were prevented by the seatbelt. Among the belted group, severe injuries did occur to the head, neck, and abdominal regions. It is recommended that both air bags and automatic restraining devices be required for all drivers if the trauma occurring daily on highways is to be eliminated and acute hospital cost minimized.

Rupture of thoracic aorta caused by blunt trauma. A fifteen-year experience.

During the 15 years from 1971 through 1985, 114 patients with rupture of the thoracic aorta caused by blunt trauma were admitted to the Shock Trauma Center of the Maryland Institute for Emergency Medical Services Systems. Mean age was 31.3 years (range, 15 to 80). Ninety were male and 24 were female, a 3.75:1 ratio. Of the 114, 89 (78.1%) survived initial resuscitation in the admitting area. Twenty five of the 89 initial survivors (28.1%) died during or after surgical repair. Paraplegia occurred in 11 of the 78 operating room survivors (14.1%). Further analysis was done of the 83 patients admitted in the 10-year period from 1976 through 1985. Mean Injury Severity Score, excluding aortic injury, was 18.2. Twenty-five of the 83 (30.1%) died during resuscitation in the admitting area or operating room. Seven others died during surgical repair and 12 died postoperatively, leaving 39 survivors (39/83 [47%] of total admissions and 39/58 [67.2%] of survivors of resuscitation). Paraplegia/paresis developed postoperatively in six of 34 (17.6%) cases involving shunt and four of 17 (23.5%) without shunt. Other major complications occurred in 21 of the operating room survivors. Statistically significant risk of death or major complication was associated with female sex, higher Injury Severity Score, lower admission blood pressure, larger hemothorax on admission, less qualified surgeon, major operation before aortic repair, use of shunt, and transfer directly from scene of injury. There was no advantage in this series to using or not using a shunt in preventing paraplegia. Mortality rates are realistic for a highly developed trauma system. Better techniques are needed to manage exsanguination and prevent paraplegia.

Blunt traumatic pericardial rupture. A ten-year experience 1979 to 1989.

Blunt traumatic pericardial rupture is rarely diagnosed preoperatively and is associated with high mortality. During a ten-year period from 1979 to 1989 over 20,000 patients were admitted to a major trauma center and 22 were found to have blunt traumatic pericardial rupture. Sixteen of the 22 (72.7%) were injured in vehicle accidents, 3 (13.6%) in motorcycle crashes, and 2 (9.1%) in falls; 1 (4.5%) was crushed. Eighteen (81.8%) were diagnosed intraoperatively during resuscitation or surgery for associated injuries, and four (18.1%) were diagnosed preoperatively with pericardial window. Eighteen were males and four were females. The median age was 40.14 years (range, 17 to 68). The tears were found at the following sites: left pleuropericardial (14/22 [64%]), diaphragmatic (4/22 [18%]), right pleuropericardial (2/22 [9%]), and superior mediastinal (2/22 [9%]). Associated cardiac injuries were found in only 5 of the 22 (22.7%); all of those patients died. The overall mortality rate was 63.6% (14/22). A high index of suspicion should alert the trauma surgeon to make the diagnosis intraoperatively during emergency surgical resuscitation in the hemodynamically unstable patient and by pericardial window in the stable patient.

HIV infection rates in a trauma center treating predominantly rural blunt trauma victims.

Human immunodeficiency virus (HIV) infection rates among 1,497 consecutive adult trauma victims triaged from rural and urban sectors to a statewide trauma center in Baltimore were studied. Those studied were 71.7% men, 77.4% whites, 63.2% vehicular trauma victims, 11.2% assault victims, and 25.7% other trauma victims. Non-Baltimoreans predominated (86.0%) and 32.7% were 25 to 39 years of age. Overall, 1.67% of the victims were HIV antibody positive. Significantly higher infection rates were seen in men (1.96% vs. 0.95%; p less than 0.02), non-whites (4.13% vs. 0.95; p less than 0.005), assault victims compared with vehicular and other trauma victims (5.99% vs. 1.06% vs. 1.30%, respectively; p less than 0.001), and Baltimore City residents (3.81% vs. 1.32%; p less than 0.03). Among those 25 to 39 years of age, 68.0% of the HIV infections were noted. Results suggest that HIV infection rates among trauma center patients are a reflection of the patient population served.

Blunt chest trauma in the elderly.

Significant differences were identified between a group of elderly patients (65 years and older) and a nonelderly group both with blunt thoracic trauma. There was a lower incidence of elderly patients presenting in shock; however, cardiopulmonary arrest at arrival was more frequent in this group. Although the types of complications were similar in both populations, the morbidity and mortality rates were higher in the elderly. A high index of suspicion must be generated for an elderly patient who has sustained blunt chest trauma. An aggressive diagnostic and therapeutic approach may lead to a decrease in the high morbidity and mortality rates in the elderly.

Marijuana and alcohol use among 1023 trauma patients. A prospective study.

Marijuana use prior to injury was determined prospectively in 1023 patients injured as the result of vehicular (67.6%) and nonvehicular (32.4%) trauma. Most were men (72.8%); most were 30 years of age or younger (58.4%). All were admitted directly from the scene of injury. Serum delta-9-tetrahydrocannabinol activity was ascertained using a radioimmunoassay. Activity of 2 ng/mL or more was detected in 34.7% of subjects. Blood alcohol determinations were made in 1006 patients; 33.5% were positive. Marijuana use among vehicular and nonvehicular trauma victims was not significantly different. Marijuana use was higher among those 30 years of age or younger and among men. Vehicular crash victims consumed alcohol more frequently. Use of marijuana and alcohol in combination (16.5%) was highly significant compared with marijuana alone (18.3%), alcohol alone (16.1%), or neither drug (49.1%).

A national alcohol and trauma center survey. Missed opportunities, failures of responsibility.

The results of a national survey of trauma centers concerning their assessment and response to the problem of alcohol and trauma are reported. Surveys were returned from 154 trauma centers located in 43 states and the District of Columbia. The profile of the 125,000 patients treated at the centers is a 30-year-old man sustaining blunt trauma, usually in a vehicular crash. Two-thirds of centers estimated that the majority of their patients had abused alcohol. While acknowledging alcohol as a significant cause of trauma, only 55.2% of centers routinely obtain admitting blood alcohol levels. Less than a third of the centers employ alcoholism counselors. Most trauma centers are not providing services that allow them to fulfill their responsibility to detect and initiate treatment of alcohol abuse, a major cause of traumatic injury.