Singlet-triplet excitations in the unconventional spin-Peierls TiOBr compound.

We have performed time-of-flight neutron scattering measurements on powder samples of the unconventional spin-Peierls compound TiOBr using the fine-resolution Fermi chopper spectrometer (SEQUOIA) at the Spallation Neutron Source at Oak Ridge National Laboratory. These measurements reveal two branches of magnetic excitations within the commensurate and incommensurate spin-Peierls phases, which we associate with n=1 and n=2 triplet excitations out of the singlet ground state. These results represent the first direct measurement of the singlet-triplet energy gap in TiOBr, which has a value of E(g)=21.2±1.0 meV.

Two-dimensional kagome correlations and field induced order in the ferromagnetic XY pyrochlore Yb2Ti2O7.

Neutron scattering measurements show the ferromagnetic XY pyrochlore Yb2Ti2O7 to display strong quasi-two-dimensional (2D) spin correlations at low temperature, which give way to long range order (LRO) under the application of modest magnetic fields. Rods of scattering along 111 directions due to these 2D spin correlations imply a magnetic decomposition of the cubic pyrochlore system into decoupled kagome planes. A magnetic field of approximately 0.5 T applied along the [110] direction induces a transition to a 3D LRO state characterized by long-lived, dispersive spin waves. Our measurements map out a complex low temperature-field phase diagram for this exotic pyrochlore magnet.

A fiber-optic DNA biosensor microarray for the analysis of gene expression.

A fiber-optic biosensor array is described for the simultaneous analysis of multiple DNA sequences. A bundle of optical fibers was assembled with each fiber carrying a different oligonucleotide probe immobilized on its distal end. Hybridization of fluorescently labeled complementary oligonucleotides to the array was monitored by observing the increase in fluorescence that accompanied binding. The approach enables fast (< 10 min) and sensitive (10 nM) detection to multiple DNA sequences simultaneously, with the potential for quantitative hybridization analysis.

Corneal ulcers associated with contact lens wear.

We reviewed the experience with ulcerative keratitis associated with contact lens wear at Wills Eye Hospital, Philadelphia, from Jan 1, 1978 through July 1, 1983. Of the 322 cases of ulcerative keratitis, 56 cases (17%) were associated with the use of contact lenses. Twenty-nine (52%) of the 56 cases of contact lens-associated ulcers were culture positive. Pseudomonas was the most common isolate, occurring in 13 (23%) of the 56 cases. Staphylococcus species were the second most common, occurring in 11 (20%) of the 56 cases. In this series, contact lens-associated ulcers were seen frequently in those wearing soft lenses (48/56 cases or 86%) and in those wearing aphakic lenses (32/56 cases or 57%). Contact lens use is an increasingly important risk factor for the development of corneal ulcers. Prompt, appropriate, and intensive treatment is necessary to prevent visual loss.

Interferon treatment of adenoviral conjunctivitis.

We conducted a randomized, double-masked, placebo-controlled study to evaluate the efficacy of topical interferon in the treatment of adenoviral conjunctivitis. The study was designed to determine the efficacy of plasmid-derived alpha-2 interferon treatment with regard to the duration of clinical disease, virus shedding, and the occurrence of bilateral infection and subepithelial infiltrates. Interferon therapy was not found to have a statistically significant effect with regard to these factors in the 14 patients who completed 14 days of treatment in the study with interferon or a placebo. Interferon therapy was, however, associated with a tendency toward asymptomatic infection in the second eye when compared to the controls.

Corneal ulcers in patients with cosmetic extended-wear contact lenses.

Although cosmetic extended-wear contact lenses are generally safe, they can be associated with a number of complications. A review of 124 cases of corneal ulcers treated between Jan. 1, 1982, and June 1, 1983, disclosed six cases in otherwise healthy patients (four women and two men, ranging in age from 15 to 41 years) who wore extended-wear contact lenses for correction of myopia. In five of the six, the contact lenses had undergone recent manipulation. Two patients had changed their contact lenses without proper disinfection procedures. Five of the six had been treated with antibiotics before corneal scrapings were cultured and three had been treated with corticosteroids. The cultures grew gram-negative rods (in three cases Pseudomonas organisms and in one case Serratia organisms); both patients whose cultures grew no organisms had received antibiotics. Vigorous treatment with tobramycin and cefazolin eyedrops and cycloplegics produced final corrected visual acuities of 20/20, 20/30, 20/60, 20/20, and 20/50. In the sixth case, the final uncorrected visual acuity was counting fingers at 1 foot.

Diagnosis and management of Acanthamoeba keratitis.

Diagnosis and management of Acanthamoeba chronic ulcerative keratitis is difficult. Two cases of Acanthamoeba keratitis at Wills Eye Hospital were diagnosed within several months of each other during 1983. Corneal transplantation was necessary for diagnosis and therapy in these cases. Another two cases were diagnosed when histopathologic specimens from penetrating keratoplasties done between 1974 and 1983 were reviewed retrospectively. There has been no evidence of recurrent disease in any of our cases during follow-up periods averaging two years (range, 12 to 40 months). The diagnosis of Acanthamoeba keratitis must be considered in cases of chronic progressive corneal ulceration unresponsive to medical therapy.

Hemodynamics of interposed abdominal compression during human cardiopulmonary resuscitation.

OBJECTIVE: Clinical studies of interposed abdominal compression CPR (IAC-CPR) have had diverse outcomes. This study compared the hemodynamics of standard CPR and IAC-CPR in humans. METHODS: A 24-month prospective nonrandomized analysis of hemodynamic parameters was performed in a convenience cohort of 20 adults who had out-of-hospital, nontraumatic, normothermic cardiac arrests. The study took place in the resuscitation unit of a large urban hospital. Thoracic aortic and right atrial catheters were inserted and pressures were recorded during standard CPR and IAC-CPR. Coronary perfusion pressures (CPPs) were determined during standard CPR and IAC-CPR. The patients were separated into two groups based upon their responses to IAC-CPR. Responders had increases in CPP during IAC-CPR; nonresponders had decreases or no change in CPP during IAC-CPR. Aortic relaxation, right atrial relaxation, aortic compression, and right atrial compression phase pressures were compared between the two groups. RESULTS: CPPs increased in 13 patients and decreased in seven patients. The mean change in CPP with IAC-CPR was an increase of 5.8 +/- 15.1 torr. An elevated right atrial compression phase pressure (RaComp) during standard CPR was predictive of an increase in CPP during IAC-CPR (p = 0.047). In those patients who showed improvements in CPP during IAC-CPR, mean aortic relaxation phase pressures (AoRelax) increased by 9.5 +/- 14.2 torr (p = 0.026) and mean right atrial relaxation phase pressures (RaRelax) decreased by 2.6 +/- 6.2 torr (p = 0.099) during IAC-CPR. CONCLUSIONS: The variable effects of IAC-CPR on CPP appear to be multifactorial. The improvement in CPP that occurred in responders to IAC-CPR was secondary to an increase in AoRelax as well as a decrease in RaRelax.

A comparison of 15 year old children with excellent occlusion and with crowding of the teeth, Angle Class I malocclusion, in respect of face size and shape and tooth size.

The biological conflict that manifests itself in crowding of the teeth in man has fascinated orthodontists for generations. Correlations between tooth size and tooth arrangement can be shown, but such correlations tend to leave much unexplained in practical terms. The present report presents data from a preliminary examination of face size and shape and tooth size in boys and girls of 15-16 years, of which 47 had excellently arranged teeth and 91 showed crowding. Measurements were taken from lateral and posteroanterior cephalometric X-ray films and from dental casts. The statistical test used was the standard student t-test. Girls' faces were found to be on average significantly smaller than boys' whether the teeth were well arranged or were crowded. The comparisons of face size and shape of boys and girls with well arranged teeth with the faces of those with crowded teeth was less definite in its outcome. Girls' total tooth substance was on average significantly smaller than boys' whether the teeth were well arranged or crowded. Boys and girls with crowded teeth had a larger mean total tooth size than boys and girls with well arranged teeth.

The physical characteristics of the stabilized canine retractor.

The design, construction and a brief indication of the advantages of the stabilized canine retractor have already been explained (Adams, 1983). It is the purpose of the present investigation to clarify and evaluate the physical characteristics of the new form and to ascertain the precise nature and degree of the differences between it and the hitherto widely used standard form of this spring.

Cranial base and jaw relationship.

The lateral skull radiographs of 124 boys aged approximately 10 years divided equally between the four angle classes were digitized in an effort to establish the relationship between cranial base size and shape and jaw relationship. Comparison of the means for occlusal groups showed a trend from class II to class III as cranial base dimensions and angle decreased. The condyle was also more distally positioned with respect to nasion, point A and the Pterygomaxillary vertical in the class II groups. Cranial base length correlated strongly with maxillary length but weakly with mandibular length. Nevertheless, the size of the maxilla did not influence its prognathism. The cranial base angle was strongly correlated (-0.7) with angle sella-nasion-point B. It is concluded that cranial base size and shape influence mandibular prognathism by determining the anteroposterior position of the condyle relative to the facial profile.

Meralgia paresthetica: a complication of laparoscopic herniorrhaphy.

Laparoscopic herniorrhaphy is a new and presently evolving technique applied to the repair of inguinal defects. Many different authors have described various methods by which this can be achieved. Some of these include the transabdominal preperitoneal approach, the plug technique, the intraperitoneal onlay of mesh, and the extraperitoneal approach. The authors have performed 252 laparoscopic hernia repairs utilizing a form of the transabdominal preperitoneal procedure that is referred to as the "transperitoneal anatomic approach." The development of new procedures or the modification of existing procedures can create new problems or alter the pattern of traditional complications. These problems must be thoroughly evaluated and reported if repetition of these errors is to be avoided. Five cases of meralgia paresthetica are reported that resulted from staple entrapment of the lateral femoral cutaneous nerve during laparoscopic herniorrhaphy. An understanding of the preperitoneal inguinal anatomy and precise placement of staples will allow avoidance of this complication.

Isolation and chromosomal assignment of 100 highly informative human simple sequence repeat polymorphisms.

One hundred highly informative simple sequence repeat (SSR) polymorphisms have been isolated and mapped to specific human chromosomes by somatic cell hybrid analysis. These markers include 97 (CA)n, 2 (AGAT)n, and a single (AACT)n repeat. All the SSRs have heterozygosities greater than 0.50 and can be amplified using identical PCR conditions. At least one SSR was detected on every chromosome, except for chromosomes 22 and Y. The frequency of (CA)n repeats on each chromosome was proportional to the relative chromosomal length, except for chromosome 15, on which a substantial excess of markers was identified.