Valley Splitting in Silicon from the Interference Pattern of Quantum Oscillations.

We determine the energy splitting of the conduction-band valleys in two-dimensional electrons confined in silicon metal oxide semiconductor Hall-bar transistors. These silicon metal oxide semiconductor Hall bars are made by advanced semiconductor manufacturing on 300 mm silicon wafers and support a two-dimensional electron gas of high quality with a maximum mobility of 17.6×10^{3} cm^{2}/Vs and minimum percolation density of 3.45×10^{10} cm^{-2}. Because of the low disorder, we observe beatings in the Shubnikov-de Haas oscillations that arise from the energy splitting of the two low-lying conduction band valleys. From the analysis of the oscillations beating patterns up to T=1.7 K, we estimate a maximum valley splitting of ΔE_{VS}=8.2 meV at a density of 6.8×10^{12} cm^{-2}. Furthermore, the valley splitting increases with density at a rate consistent with theoretical predictions for a near-ideal semiconductor-oxide interface.

Spin polarization dependence of the coulomb drag at large r(s).

We find that the temperature dependence of the drag resistivity between two dilute two-dimensional hole systems exhibits an unusual dependence upon spin polarization. Our main observation is that near the apparent metal-insulator transition, the temperature dependence of the drag, given by Talpha, weakens significantly with the application of a parallel magnetic field (B(||)), with alpha saturating at half its zero field value for B(||)>B(*), where B(*) is the polarization field.

Role of density imbalance in an interacting bilayer hole system.

We study interacting GaAs hole bilayers in the limit of zero interlayer tunneling. When the layers have equal density, we observe a phase-coherent bilayer quantum Hall state (QHS) at a total filling factor nu=1, flanked by a reentrant insulating phase at nearby fillings which suggests the formation of a pinned, bilayer Wigner crystal. As we transfer charge from one layer to another, the phase-coherent QHS becomes stronger, evincing its robustness against charge imbalance, but the insulating phase disappears, suggesting that its stability requires the commensurability of the two layers.

In-plane magnetodrag between dilute two-dimensional systems.

We performed in-plane magnetodrag measurements on dilute double layer two-dimensional hole systems, at in-plane magnetic fields that suppress the apparent metallic behavior, and to fields well above those required to fully spin polarize the system. When compared to the single layer magnetoresistance, the magnetodrag exhibits exactly the same qualitative behavior. In addition, we have found that the enhancement to the drag from the in-plane field exhibits a strong maximum when both layer densities are matched.

Chondrocyte apoptosis following intraarticular fracture in humans.

OBJECTIVE: The primary objective of the present study was to establish the degree to which chondrocyte apoptosis occurs in vivo following intraarticular fractures in humans. DESIGN: Fracture cartilage specimens were obtained from patients undergoing surgical intervention for fractures of the articular surface of the proximal tibia. Normal proximal tibia cartilage specimens served as controls. Apoptotic chondrocytes were identified and quantified using TUNEL analysis. RESULTS: The percentage of TUNEL positive chondrocytes in the fractured articular cartilage specimens (mean 18.5%, range 1-44%) was found to be an order of magnitude higher than the percentage observed in control specimens (mean 1.9%, range 0-4%). CONCLUSIONS: The percentage of TUNEL positive chondrocytes following intraarticular fracture is much higher than that reported for chronic degenerative conditions such as osteoarthritis and rheumatoid arthritis. These data provide strong evidence that chondrocyte apoptosis is a consequence of intraarticular fracture and suggest that chondrocyte apoptosis may play a particularly significant role in the subsequent development of post-traumatic arthritis.

Frictional drag between two dilute two-dimensional hole layers.

We report drag measurements on dilute double layer two-dimensional hole systems in the regime of r(s) = 19-39. We observed a strong enhancement of the drag over the simple Boltzmann calculations of Coulomb interaction, and deviations from the T2 dependence which cannot be explained by phonon-mediated, plasmon-enhanced, or disorder-related processes. We suggest that this deviation results from interaction effects in the dilute regime.

Possible molecular mechanisms of cryoablation-induced impotence in a rat model.

OBJECTIVES: Cryoablation of the prostate has been reported to induce impotence as a consequence of cavernosal nerve injury. This study is designed to investigate the early and late effects of cavernosal nerve cryoablation on growth factor expression and erectile function in a rat model. METHODS: Forty male rats were divided into two groups (n=20 each). The first group underwent unilateral cavernosal nerve freezing (experimental group). Before their euthanization at 1 and 3 months (10 rats each), erectile function was assessed by electrostimulation of the cavernous nerves. The second group served as the control and was killed at the same time points. Western blot and reverse transcriptase-polymerase chain reaction (RT-PCR) techniques were used to identify protein and gene expression of nerve growth factor (NGF), transforming growth factor-alpha (TGF-alpha), epidermal growth factor (EGF), and insulin-like growth factor-1 (IGF-1) in the rat penis and pelvic ganglia. RESULTS: Electrostimulation of the frozen nerve after 3 months revealed a significantly higher maximal intracavernosal pressure and a shorter latency period than in the 1-month group. At 3 months, immunoblot showed upregulation of NGF, TGF-alpha, and the precursor form of IGF-1 protein expression in the penile tissue; RT-PCR showed downregulation of NGF gene expression in the pelvic ganglia of the frozen side. CONCLUSIONS: The results show that erectile function decreased at 1 month and then partially recovered 3 months after cavernosal nerve freezing. This alteration in erectile function was associated with differential gene and protein expression of the growth factors (NGF, TGF-alpha, EGF, and IGF-1). Further studies are required to elucidate the potential role of these growth factors in the prevention and treatment of cryoablation-induced impotence.

Peyronie's disease is associated with an increase in transforming growth factor-beta protein expression.

PURPOSE: Transforming growth factor-beta (TGF-beta) has been implicated in many chronic fibrotic conditions such as pulmonary and hepatic fibrosis. We postulated that TGF-beta may play a role in the pathogenesis of Peyronie's disease. MATERIALS AND METHODS: Tissues from the tunica albuginea of 30 Peyronie's disease patients (study group) and from 6 patients without Peyronie's disease, who had undergone penile prosthesis surgery for organic impotence (control group), were subjected to histological examination using Hart and trichrome stains and Western blotting for the detection of TGF-beta protein expression. RESULTS: The results of these experiments demonstrate that all tissue from Peyronie's disease patients showed a variety of histological changes of the tunica, ranging from chronic inflammatory cellular infiltration to complete calcification and ossification of the tissues. The most prominent changes observed in the majority of patients were focal or diffused elastosis, fenestration and disorganization of the collagen bundles. TGF-beta1 protein expression was detected in 26 patients (86%), while only 7 (23%) and 5 (17%) patients showed TGF-beta2 and TGF-beta3 protein expression, respectively. One patient in the control group showed fibrosis of the tunica albuginea and protein expression of TGF-beta1 and TGF-beta2. This patient had undergone surgery for the revision of his prosthesis twice. Five patients from the control group showed normal histological patterns of the tunica albuginea and no protein expression for TGF-beta1, TGF-beta2 and TGF-beta3. CONCLUSIONS: TGF-beta1 protein expression is significantly associated with Peyronie's disease, which may provide a new insight and the potential for the prevention and treatment of this disease.

Discordant distribution of IgM and IgG antibodies to DNA and RNA in monozygotic twins with systemic lupus erythematosus.

Sera from six sets of twins (five monozygotic and one dyzygotic) in whom one or both has systemic lupus erythematosus (SLE) were evaluated for antibodies to DNA and RNA. Sera from three monozygotic twin sets were further studied to determine the distribution of 19S and 7S antibodies to DNA and RNA. The presence of significant binding of polyriboadenylic acid and of native DNA correlated with the presence of clinical SLE in this study. Sucrose density gradient fractionation studies of the sera revealed that the clinically normal twins had some binding of Poly A and DNA limited to the 19S region, whereas the twins with SLE generally had significant levels of 19S and 7S antibodies to DNA and/or Poly A. On the other hand, concordance for presence or absence of antibodies to doublestranded RNA was demonstrated within each twin set irrespective of concordance or discordance for clinical SLE. These results suggest that genetic factors may be important in determining which nucleic acids antigens become immunogenic, but genetic factors alone do not determine the immunoglobulin class distribution of antibodies to nucleic acids.

Lymphocytes binding polyriboadenylic acid and synthesizing antibodies to nucleic acids in autoimmune and normal mice.

Splenic lymphocytes from both normal and autoimmune mice bind significant quantities of polyriboadenylic acid (poly rA) when incubated with radiolabeled poly rA for 40 min at 37 degrees C. This poly rA binding is specifically inhibited by an excess of nonradioactive poly rA and by anti-mouse immunoglobulin. Poly rA binding is decreased by exposing spleen cells to Pronase and is restored by subsequent culture for 18 to 72 hr. Poly rA-binding activity is associated more with bone marrow-derived than with thymus-derived lymphocytes. These results suggest the presence of autoantigen-binding lymphocytes in normal as well as autoimmune mice. Furthermore, spleen cells from normal and autoimmune mice cultured for 72 hr synthesize and secrete antibodies to poly rA and DNA. These antibodies can be recovered from the culture supernatants by a solid immunoadsorbent technique and antibody immunoprecipitation. The synthesis of antibodies to nucleic acids by normal spleen cells suggests that autoreactive lymphocytes may be released from normal immunoregulatory control during in vitro culture conditions.

Immunological regulation of spontaneous antibodies to DNA and RNA. II. Sequential switch from IgM to IgG in NZB/NZW F1 mice.

Serial serum samples from NZB/NZW F1 mice were studied by sucrose density gradient ultracentrifugation and filter radioimmunoassay for the immunoglobulin class of antibodies to double-stranded DNA and single-stranded RNA (Poly A). These antibodies occur spontaneously during the course of an autoimmune disease resembling systemic lupus erythematosus. Study of serum samples at 2-week intervals showed the sequential appearance of 19S followed by 7S anti-nucleic acid antibodies, an earlier commitment to 7S antibodies in female compared to male mice, and an independent and unrelated switching mechanism (19S-7S) for antibodies to DNA and Poly A. The more severe disease in female mice is correlated with an earlier appearance of 7S anti-DNA antibodies. This sequential and ordered appearance of antibodies to nucleic acids is discussed in relation to possible immunologic regulatory mechanisms.

Immunologic regulation of spontaneous antibodies to DNA and RNA I. Significance of IgM and IgG antibodies in SLE patients and asymptomatic relatives.

Nine individuals from four families of patients with systemic lupus erythematosus (SLE) were studied by sucrose density gradient fractionation and filter radioimmunoassay for the presence of 19S IgM and 7S IgG antibodies to DNA, poly rA, and poly rA-poly rU. One individual in each family was totally asymptomatic, and at least one had actively systemic lupus erythematosus (SLE). The results indicate: (1) a correlation between 7S antibody to DNA and RNA and active SLE, and (2) the presence of 19S antibody to RNA in the asymptomatic relatives. These findings suggest that SLE may be a disorder of immunological regulation. The distribution of antibodies between IgM and IgG is closely related to disease severity. the asymptomatic relatives may have a partial regulatory abnormality resulting in the limited production of IgM antibodies to RNA. SLE patients may have a more complex failure of regulation permitting the additional synthesis of IgG antibodies to DNA and RNA.