Photonic crystals as topological high-Q resonators.

It is well known that defects, such as holes, inside an infinite photonic crystal can sustain localized resonant modes whose frequencies fall within a forbidden band. Here we prove that finite, defect-free photonic crystals behave as mirrorless resonant cavities for frequencies within but near the edges of an allowed band, regardless of the shape of their outer boundary. The resonant modes are extended, surface-avoiding (nearly-Dirichlet) states that may lie inside or outside the light cone. Independent of the dimensionality, quality factors and finesses are on the order of, respectively, (L/λ)3 and L/λ, where λ is the vacuum wavelength and L >> λ is a typical size of the crystal. Similar topological modes exist in conventional Fabry-Pérot resonators, and in plasmonic media at frequencies just above those at which the refractive index vanishes.

Observation of standing waves of electron-hole sound in a photoexcited semiconductor.

Three-dimensional multicomponent plasmas composed of species with very different masses support a new branch of charge-density fluctuations known as acoustic plasmons. Here, we report on an ultrafast optical method to generate and probe coherent states of acoustic plasmons in a slab of GaAs, which relies on strong photoexcitation to create a large population of light electrons and heavy holes. Consistent with the random-phase-approximation theory, the data reveal standing plasma waves confined to these slabs, similar to those of conventional sound but with associated velocities that are significantly larger.

Dirac semimetal in three dimensions.

We show that the pseudorelativistic physics of graphene near the Fermi level can be extended to three dimensional (3D) materials. Unlike in phase transitions from inversion symmetric topological to normal insulators, we show that particular space groups also allow 3D Dirac points as symmetry protected degeneracies. We provide criteria necessary to identify these groups and, as an example, present ab initio calculations of ß-cristobalite BiO(2) which exhibits three Dirac points at the Fermi level. We find that ß-cristobalite BiO(2) is metastable, so it can be physically realized as a 3D analog to graphene.

A comparative study of high-resolution cone beam computed tomography and charge-coupled device sensors for detecting caries.

OBJECTIVES: Conventional radiographic imaging of teeth underestimates the presence of caries. The objective of this study was to compare the efficacy of high-resolution cone beam CT (CBCT) images and conventional charge-coupled device (CCD) images for detecting proximal and occlusal caries. METHODS: Non-restored, extracted human permanent premolar and molar teeth were mounted and then imaged with a 3DX Accuitomo and a CCD. We selected 92 occlusal and 100 proximal surfaces for raters to score. Of these, 36 and 25, respectively, had lesions extending into dentin. Using a five-step confidence scale, eight practising dentists evaluated the images for the presence of caries in dentin using both modalities. Actual presence and extent of caries was established with microCT imaging. RESULTS: For proximal surface lesions extending into dentin, the average sensitivity score using 3DX images (0.61) was almost twice that of CCD images (0.33) and the difference was significant. The specificity values for both systems were high and not significantly different from each other. For occlusal surfaces, raters detected significantly more lesions in the enamel or dentin when using the 3DX images than when using CCD images. However, the raters also had significantly lower average specificity scores for the 3DX images compared with the CCD images for lesions at both depths. CONCLUSIONS: Practising dentists were able to improve their detection of proximal-surface caries extending into the dentin, but not occlusal caries, using 3DX high-resolution cone beam CT images compared with CCD images.

Detection of perchlorate and the soluble chemistry of martian soil at the Phoenix lander site.

The Wet Chemistry Laboratory on the Phoenix Mars Lander performed aqueous chemical analyses of martian soil from the polygon-patterned northern plains of the Vastitas Borealis. The solutions contained approximately 10 mM of dissolved salts with 0.4 to 0.6% perchlorate (ClO4) by mass leached from each sample. The remaining anions included small concentrations of chloride, bicarbonate, and possibly sulfate. Cations were dominated by Mg2+ and Na+, with small contributions from K+ and Ca2+. A moderately alkaline pH of 7.7 +/- 0.5 was measured, consistent with a carbonate-buffered solution. Samples analyzed from the surface and the excavated boundary of the approximately 5-centimeter-deep ice table showed no significant difference in soluble chemistry.

Evidence for calcium carbonate at the Mars Phoenix landing site.

Carbonates are generally products of aqueous processes and may hold important clues about the history of liquid water on the surface of Mars. Calcium carbonate (approximately 3 to 5 weight percent) has been identified in the soils around the Phoenix landing site by scanning calorimetry showing an endothermic transition beginning around 725 degrees C accompanied by evolution of carbon dioxide and by the ability of the soil to buffer pH against acid addition. Based on empirical kinetics, the amount of calcium carbonate is most consistent with formation in the past by the interaction of atmospheric carbon dioxide with liquid water films on particle surfaces.

Repression of Gadd45alpha by activated FLT3 and GM-CSF receptor mutants contributes to growth, survival and blocked differentiation.

The tumor suppressor Gadd45alpha was earlier shown to be a repressed target of sustained receptor-mediated ERK1/2 signaling. We have identified Gadd45alpha as a downregulated gene in response to constitutive signaling from two FLT3 mutants (FLT3-ITD and FLT3-TKD) commonly found in AML, and a leukemogenic GM-CSF receptor trans-membrane mutant (GMR-V449E). GADD45A mRNA downregulation is also associated with FLT3-ITD(+) AML. Sustained ERK1/2 signaling contributes significantly to receptor-mediated downregulation of Gadd45alpha mRNA in FDB1 cells expressing activated receptor mutants, and in the FLT3-ITD(+) cell line MV4;11. Knockdown of Gadd45alpha with shRNA led to increased growth and survival of FDB1 cells and enforced expression of Gadd45alpha in FDB1 cells expressing FLT3-ITD or GMR-V449E resulted in reduced growth and viability. Gadd45alpha overexpression in FLT3-ITD(+) AML cell lines also resulted in reduced growth associated with increased apoptosis and G(1)/S cell cycle arrest. Overexpression of Gadd45alpha in FDB1 cells expressing GMR-V449E was sufficient to induce changes associated with myeloid differentiation suggesting Gadd45alpha downregulation contributes to the maintenance of receptor-induced myeloid differentiation block. Thus, we show that ERK1/2-mediated downregulation of Gadd45alpha by sustained receptor signaling contributes to growth, survival and arrested differentiation in AML.

The detection of small relative simulated field defects using multifocal VEPs.

INTRODUCTION: The multifocal visual-evoked potential (mfVEP) has been widely used in the study of diseases of the visual system. However, the sensitivity of the mfVEP in the objective detection of relative field defects has not been determined. This study investigates variations in mfVEP responses while simulating relative field defects by using different luminous transmission masks [neutral density (ND) filters] on the stimulus pattern. METHODS: Simulated relative field defects with four different luminous transmissions were obtained by using 0.2, 0.4, 0.6, and 0.8 ND filters, 5 degrees in size, at two different retinal eccentricities (10 and 16 degrees) on a standard mfVEP dartboard stimulus. Eleven normal subjects were recruited for mfVEP measurements. The response amplitudes and latencies of the N1 and P1 of the mfVEP, with and without small simulated relative field defects, were compared. RESULTS: The mfVEP amplitudes of N1 and P1 decreased substantially when 0.6 and 0.8 ND filters were introduced. The effects were similar at both the 10- and 16-degree eccentricities but there was no change in latency with simulated field defects at either location. CONCLUSIONS: The mfVEP can detect a simulated relative field defect 5 degrees in size starting with 0.6 log unit reduction in luminance at both 10-degree and 16-degree eccentricities. This illustrates that the sensitivity of the mfVEP measurement is nearly comparable with that of the Humphrey Visual Field Analyser.

Adeno-associated virus (AAV) site-specific recombination does not require a Rep-dependent origin of replication within the AAV terminal repeat.

Adeno-associated virus (AAV) is the only known eukaryotic virus capable of targeted integration in human cells. An AAV Rep binding element (RBE) and terminal resolution site (trs) identical to the viral terminal repeats required for AAV DNA replication are located on chromosome (ch) 19. Both ch-19 RBE and trs elements have been shown to be essential for viral targeting to this locus. To characterize the role of the AAV inverted terminal repeat (ITR) cis-acting sequences in targeted integration an AAV trs mutant incapable of supporting viral replication was tested. Wild-type and mutant substrates were assayed for targeted integration after cotransfection in the presence or absence of Rep. Our results demonstrated that, in the presence of Rep78, both ITR substrates targeted to ch-19 with similar frequency. Molecular characterization of the mutant ITR integrants confirmed the presence of the trs mutation in the majority of samples tested. Complementation analysis confirmed that the mutant targeted viral genomes were unable to rescue and replicate. In addition, Rep78 induced extensive rearrangement and amplification of ch-19 sequences independent of wild-type or mutant targeting substrate. These studies demonstrate that Rep-dependent nicking of the viral cis-acting trs sequence is not a prerequisite for site-specific recombination and suggests AAV targeting is mediated by Rep78/68-dependent replication from the ch-19 origin of replication (ori). These studies have significant impact toward the understanding of AAV site-specific recombination and the development of targeting vectors.

Acute rejection-associated tubular basement membrane defects and chronic allograft nephropathy.

BACKGROUND: Acute rejection is a major risk factor for chronic allograft nephropathy, although the link(s) between these events is not understood. The hypothesis of this study is that alterations in tubular basement membranes (TBMs) that occur during acute rejection may be irreversible and thereby play a role in the development of chronic allograft nephropathy. METHODS: Fourteen renal transplant patients were selected, each having had two or more biopsies performed (42 total). All biopsies were scored for acute and chronic rejection using Banff 1997 criteria. The initial biopsy showed only acute interstitial rejection (type I rejection). No biopsies contained significant chronic arterial lesions of chronic vascular rejection. The entire cortex was examined on Jones methenamine silver-stained sections at x400 for interruption in TBM staining. The number of tubules with TBM abnormalities was counted, and the renal cortical area was measured by image analysis. Periodic acid-Schiff/immunoperoxidase stain was performed on 12 acute rejection biopsies stained for laminin, cytokeratin 7, CD3, CD20, and CD68. Controls consisted of 11 biopsies (8 negative for rejection and 3 acute tubular necrosis). RESULTS: Numerous TBM alterations in silver staining were identified as being associated with acute rejection and tubulitis, consisting of abrupt TBM discontinuities and/or extreme attenuation with segmental or complete absence of TBM. A loss of TBM matrix proteins was confirmed by absent laminin staining in areas of acute rejection and tubulitis. There was herniation of tubular cells into the interstitium through TBM defects confirmed by cytokeratin staining. The TBM defects were spatially associated with inflammatory cells, particularly macrophages. When the biopsies were divided into two groups, <10 and> 10 TBM breaks/mm2, there were statistically significant morphologic and clinical correlations. The number of TBM disruptions correlated with the serum creatinine at the time of biopsy, a combined Banff t + i score, the difference in tubular atrophy between the initial and most recent biopsy and the difference between the nadir creatinine and most recent creatinine. CONCLUSION: Damage to TBM develops in acute rejection as a consequence of interstitial inflammation and tubulitis. These lytic events correlate with the later development of clinical and morphologic evidence of chronic injury in the absence of arterial injury of chronic rejection. We suggest that chronic allograft nephropathy may have an inflammatory interstitial origin.

Roles of adeno-associated virus Rep protein and human chromosome 19 in site-specific recombination.

Adeno-associated virus type 2 (AAV) is the only known eucaryotic virus capable of targeted integration in human cells. AAV integrates preferentially into human chromosome (ch) 19q13.3qter. The nonstructural proteins of AAV-2, Rep78 and Rep68, are essential for targeted integration. Rep78 and Rep68 are multifunctional proteins with diverse biochemical activities, including site-specific binding to AAV and ch-19 target sequences, helicase activity, and strand-specific, site-specific endonuclease activities. Both a Rep DNA binding element (RBE) and a nicking site essential for AAV replication present within the viral terminal repeats are also located on ch-19. Recently, identical RBE sequences have been identified at other locations in the human genome. This fact raises numerous questions concerning AAV targeted integration; specifically, how many RBE sequences are in the human genome? How does Rep discriminate between these and the ch-19 RBE sequence? Does Rep interact with all sites and, if so, how is targeted integration within a fixed time frame facilitated? To better characterize the role of Rep in targeted integration, we established a Rep-dependent filter DNA binding assay using a highly purified Rep-68 fusion protein. Electron microscopy (EM) analysis was also performed to determine the characteristics of the Rep-RBE interaction. Our results determined that the Rep affinity for ch-19 is not distinct compared to other RBEs in the human genome when utilizing naked DNA. In fact, a minimum-binding site (GAGYGAGC) efficiently associated with Rep, suggesting that as many as 2 x 10(5) sites may exist. In addition, such sites also exist frequently in nonprimate mammalian genomes, although AAV integrates site specifically into primate genomes. EM analysis demonstrated that only one Rep-DNA complex was formed on ch-19 target DNA. Surprisingly, identically sized complexes were observed on all substrates containing a RBE sequence, but never on DNA lacking an RBE. Rep-DNA complexes involved a multimeric protein structure that spanned ca. 60 bp. Immunoprecipitation of AAV latently infected cells determined that 1,000 to 4,000 copies of Rep78 and Rep68 protein are expressed per cell. Comparison of the Rep association constant with those of established DNA binding proteins indicates that sufficient molecules of Rep are present to interact with all potential RBE sites. Moreover, Rep expression in the absence of AAV cis-acting substrate resulted in Rep-dependent amplification and rearrangement of the target sequence in ch-19. This result suggests that this locus is a hot spot for Rep-dependent recombination. Finally, we engineered mice to carry a single 2.7-kb human ch-19 insertion containing the AAV ch-19 target locus. Using cells derived from these mice, we demonstrated that this sequence was sufficient for site-specific recombination after infection with transducing vectors expressing Rep. This result indicates that any host factors required for targeting are conserved between human and mouse. Furthermore, the human ch-19 cis sequences and chromatin structure required for site-specific recombination are contained within this fragment. Overall, these results indicate that the specificity of targeted recombination to human ch-19 is not dictated by differential Rep affinities for RBE sites. Instead, specificity is likely dictated by human ch-19 sequences that serve as a Rep protein-mediated origin of replication, thus facilitating viral targeting through Rep-Rep interactions and host enzymes, resulting in site-specific recombination. Control of specificity is clearly dictated by the ch-19 sequences, since transfer of these sequences into the mouse genome are sufficient to achieve Rep-dependent site-specific integration.

Charge-to-alanine mutagenesis of the adeno-associated virus type 2 Rep78/68 proteins yields temperature-sensitive and magnesium-dependent variants.

The adeno-associated virus type 2 (AAV) replication (Rep) proteins Rep78 and 68 (Rep78/68) exhibit a number of biochemical activities required for AAV replication, including specific binding to a 22-bp region of the terminal repeat, site-specific endonuclease activity, and helicase activity. Individual and clusters of charged amino acids were converted to alanines in an effort to generate a collection of conditionally defective Rep78/68 proteins. Rep78 variants were expressed in human 293 cells and analyzed for their ability to mediate replication of recombinant AAV vectors at various temperatures. The biochemical activities of Rep variants were further characterized in vitro by using Rep68 His-tagged proteins purified from bacteria. The results of these analyses identified a temperature-sensitive (ts) Rep protein (D40,42,44A-78) that exhibited a delayed replication phenotype at 32 degrees C, which exceeded wild-type activity by 48 h. Replication activity was reduced by more than threefold at 37 degrees C and was undetectable at 39 degrees C. Stability of the Rep78 protein paralleled replication levels at each temperature, further supporting a ts phenotype. Replication differences resulted in a 3-log-unit difference in virus yields between the permissive and nonpermissive temperatures (2.2 x 10(6) and 3 x 10(3), respectively), demonstrating that this is a relatively tight mutant. In addition to the ts Rep mutant, we identified a nonconditional mutant with a reduced ability to support viral replication in vivo. Additional characterization of this mutant demonstrated an Mg(2+)-dependent phenotype that was specific to Rep endonuclease activity and did not affect helicase activity. The two mutants described here are unique, in that Rep ts mutants have not previously been described and the D412A Rep mutant represents the first mutant in which the helicase and endonuclease functions can be distinguished biochemically. Further understanding of these mutants should facilitate our understanding of AAV replication and integration, as well as provide novel strategies for production of viral vectors.

Medial prefrontal cortical output neurons to the ventral tegmental area (VTA) and their responses to burst-patterned stimulation of the VTA: neuroanatomical and in vivo electrophysiological analyses.

During a delayed period in a delayed-response task, prefrontal cortical neurons show a change in neuronal firing rate that is dependent on a functional mesocortical dopamine input. This change in firing rate has been attributed to be part of the cellular processes underlying working memory. However, it is unclear what neural mechanisms activate mesocortical dopamine neurons to provide an optimal level of dopamine to modulate the firing of the medial prefrontal cortical (mPFC) neurons. This study examined the possibility of whether mPFC neurons that project to the ventral tegmental area (VTA) might activate the ascending mesocortical dopamine neurons. To determine the locations of the mPFC-->VTA neurons, cholera toxin subunit B was microinjected into the VTA. Retrogradely labeled mPFC neurons mainly reside in the deep lamina V and VI. In vivo single unit recording in urethane-anesthetized rats were also used to determine the responses of some of these neurons to burst-patterned stimulation of the VTA. Single-pulse stimulation (1 Hz) of the VTA antidromically activated burst firing mPFC-->VTA neurons. In response to burst-patterned stimulation of the VTA, which mimicked burst firing of VTA dopamine neurons (4-10 pulses at 10-15 Hz cycled at 0.5-3 Hz), the temporal structure of spontaneous burst firing patterns of these neurons but not their mean firing rate were changed. However, the mean firing rate of the non-VTA projecting neurons (i.e., no antidromic response to VTA stimulations) was either increased or decreased by similar burst-patterned stimulation of the VTA. These data suggest that burst-patterned stimulation of the ascending VTA-->mPFC or putative mesocortical dopamine neurons might have released dopamine and/or other neuromodulators to modulate the temporal code, rather than the rate code, of mPFC-->VTA neurons. Medial PFC neurons that project elsewhere (e.g., nucleus accumbens or mediodorsal thalamus) may mediate the sustained firing rate changes during, e.g., short-term working memory.

The prevalence of previous sexual assault among routine female attenders at a department of genitourinary medicine.

One hundred and fifty women who attended the routine genitourinary medicine (GUM) clinic at the Leicester Royal Infirmary (LRI) between August 1993 and February 1994 completed a questionnaire enquiring into a past history of sexual assault. Of these, 52 (34.7%) confirmed that they had been assaulted previously, 18 below the age of 16, 22 after this age and 12 in both age groups. Non penetrative abuse was most common in those violated as minors and vaginal penetration in women assaulted over the age of 16. The strongest demographic indicator for sexual abuse among this study group was that of a current divorced/separated marital status. Assailants of minors were most likely to be someone known to the family whereas male intimates accounted for a third of assaults on older women. Sexual dysfunction was acknowledged by approximately half of those previously assaulted as a sequelae of abuse. It is important that GUM physicians remain alert for sequelae of sexual abuse and offer services appropriate to the victim's needs.

Cell cycle gene expression and E2F transcription factor complexes in human melanoma cells induced to terminally differentiate.

Defects in cellular differentiation are a common occurrence in human cancers. The combination of recombinant human fibroblast interferon (IFN-beta) and the antileukemic compound mezerein (MEZ) results in an irreversible loss of proliferative capacity and terminal cell differentiation in H0-1 human melanoma cells. In contrast, either agent alone induces reversible growth arrest and/or specific components of the differentiation process without inducing terminal differentiation. The current study investigates changes in cell cycle, cell cycle gene expression and E2F transcription factor complex formation during the processes of reversible and irreversible (terminal) differentiation. Induction of both terminal differentiation and reversible differentiation (MEZ treatment) results in a temporal decrease in DNA synthesis and the percentage of cells in S phase and a decrease in the expression of cell cycle and growth regulated genes, including cdc2, cyclin A, cyclin B, histone H1, histone H4, nm23-H1, p53 and c-myc. Persistent gene expression changes occur in terminally differentiated cells, but not in reversibly differentiated cells. H0-1 cells contain several E2F binding activities, including uncomplexed E2F, an E2F-p107-cyclin A-cdk2 kinase complex and an Rb-E2F complex. Induction of growth arrest by MEZ results in a slow migrating gelshift band that contains E2F associated with the pRb2/p130 protein. There is also a loss of the Rb-E2F complex. Induction of terminal differentiation after treatment with IFN-beta + MEZ generates a second pRb2/p130-E2F complex that migrates considerably faster than the pRb2/p130-E2F complex resulting from growth arrest. The slower migrating complex may contribute to growth arrest, whereas the faster migrating complex may play a role in terminal differentiation. Our results demonstrate that terminal cell differentiation involves a co-ordinate and continuous suppression of a number of cell cycle and growth related genes and results in the development of a novel E2F transcription factor complex not apparent in growth arrested and reversibly differentiated human melanoma cells.

Disseminated candidal infections and intravenous hydrocortisone in preterm infants.

BACKGROUND: Intravenous (i.v.) hydrocortisone (HC) has been used recently in selected preterm infants for hypotension soon after birth. During the same time period that HC was used, there was a marked increase in the incidence of disseminated candidal infections (DCIs). OBJECTIVE: To determine whether there is an association between DCI in the first 35 days of life and i.v. HC in preterm infants. RESEARCH DESIGN: A hospital case-control study comparing the exposure of HC between preterm infants with DCI and matched infants without DCI. SETTING: A tertiary level intensive care nursery in a major teaching hospital in San Francisco, CA. PATIENTS: Seventeen preterm infants with DCI and 25 infants without DCI, with gestational age younger than 28 weeks and birth weight less than 1000 g, inborn and outborn admitted to the intensive care nursery between January 1992 and September 1993. METHODS: All preterm infants diagnosed with DCI at younger than 35 days of age were identified using a perinatal and neonatal database. DCI was defined as a blood, cerebrospinal fluid, or two urine cultures positive for Candida requiring antifungal therapy. A control group of uninfected infants matched for the major risk factors for DCI (gestational age, birth weight, duration of intubation, broad-spectrum antibiotics, and i.v. alimentation, including lipids and central venous catheters) admitted during the same period was identified using the same database. Postmatching comparison was performed for several other factors to detect any other differences between the groups. RESULTS: The infants with DCI (n = 17) and control infants (n = 25) had no statistical difference in exposure to the major risk factors for DCI or in postmatching comparison. Ten (59%) of the infants with DCI were receiving HC at the time of infection, whereas four (16%) of the control infants received HC during the first 35 days of life. Infants with DCI were 7.5 times as likely as control infants (95% confidence interval, 5 to 11) to have received IV HC before the onset of fungal infection. CONCLUSION: We conclude that the administration of i.v. HC significantly increases the risk of DCI in susceptible preterm infants younger than 35 days of age. The potentially serious risks of DCI should be considered particularly in the patient selection process for administration of i.v. HC.