Moiré pattern of interference dislocations in condensate of indirect excitons.

Interference patterns provide direct measurement of coherent propagation of matter waves in quantum systems. Superfluidity in Bose-Einstein condensates of excitons can enable long-range ballistic exciton propagation and can lead to emerging long-scale interference patterns. Indirect excitons (IXs) are formed by electrons and holes in separated layers. The theory predicts that the reduced IX recombination enables IX superfluid propagation over macroscopic distances. Here, we present dislocation-like phase singularities in interference patterns produced by condensate of IXs. We analyze how exciton vortices and skyrmions should appear in the interference experiments and show that the observed interference dislocations are not associated with these phase defects. We show that the observed interference dislocations originate from the moiré effect in combined interference patterns of propagating condensate matter waves. The interference dislocations are formed by the IX matter waves ballistically propagating over macroscopic distances. The long-range ballistic IX propagation is the evidence for IX condensate superfluidity.

Pancharatnam-Berry phase in condensate of indirect excitons.

The Pancharatnam-Berry phase is a geometric phase acquired over a cycle of parameters in the Hamiltonian governing the evolution of the system. Here, we report on the observation of the Pancharatnam-Berry phase in a condensate of indirect excitons (IXs) in a GaAs-coupled quantum well structure. The Pancharatnam-Berry phase is directly measured by detecting phase shifts of interference fringes in IX interference patterns. Correlations are found between the phase shifts, polarization pattern of IX emission, and onset of IX spontaneous coherence. The evolving Pancharatnam-Berry phase is acquired due to coherent spin precession in IX condensate and is observed with no decay over lengths exceeding 10 µm indicating long-range coherent spin transport.

Comparison of spinal deformity in children with Chiari I malformation with and without syringomyelia: matched cohort study.

PURPOSE: To describe curve patterns in patients with Chiari malformation I (CIM) without syringomyelia, and compare to patients with Chiari malformation with syringomyelia (CIM + SM). METHODS: Review of medical records from 2000 to 2013 at a single institution was performed to identify CIM patients with scoliosis. Patients with CIM were matched (1:1) by age and gender to CIM + SM. Radiographic curve patterns, MRI-based craniovertebral junction parameters, and associated neurological signs were compared between the two cohorts. RESULTS: Eighteen patients with CIM-associated scoliosis in the absence of syringomyelia were identified; 14 (78 %) were female, with mean age of 11.5 ± 4.5 years. Mean tonsillar descent was 9.9 ± 4.1 mm in the CIM group and 9.1 ± 3.0 mm in the CIM + SM group (p = 0.57). Average syrinx diameter in the CIM + SM group was 9.0 ± 2.7 mm. CIM patients demonstrated less severe scoliotic curves (32.1° vs. 46.1°, p = 0.04), despite comparable thoracic kyphosis (43.7° vs. 49.6°, p = 0.85). Two (11 %) patients with CIM demonstrated thoracic apex left deformities compared to 9/18 (50 %) in the CIM + SM cohort (p = 0.01). Neurological abnormalities were only observed in the group with syringomyelia (6/18, or 33 %; p = 0.007). CONCLUSION: In the largest series specifically evaluating CIM and scoliosis, we found that these patients appear to present with fewer atypical curve features, with less severe scoliotic curves, fewer apex left curves, and fewer related neurological abnormalities than CIM + SM. Notably, equivalent thoracic kyphosis was observed in both groups. Future studies are needed to better understand pathogenesis of spinal deformity in CIM with and without SM.

Two-dimensional snowflake trap for indirect excitons.

We present experimental proof of principle for two-dimensional electrostatic traps for indirect excitons. A confining trap potential for indirect excitons is created by a snowflake-shaped electrode pattern. We demonstrate collection of indirect excitons from all directions to the trap center and control of the trap potential by voltage.

Spin currents in a coherent exciton gas.

We report the observation of spin currents in a coherent gas of indirect excitons. The realized long-range spin currents originate from the formation of a coherent gas of bosonic pairs--a new mechanism to suppress the spin relaxation. The spin currents result in the appearance of a variety of polarization patterns, including helical patterns, four-leaf patterns, spiral patterns, bell patterns, and periodic patterns. We demonstrate control of the spin currents by a magnetic field. We also present a theory of coherent exciton spin transport that describes the observed exciton polarization patterns and indicates the trajectories of the spin currents.

Condensation of excitons in a trap.

Condensation is observed in a gas of indirect excitons confined in an electrostatic trap. Imaging and interferometric measurements detect that excitons condense at the trap bottom and exciton spontaneous coherence emerges with lowering temperature. Below a temperature of about 1 K, the direct signature of Bose-Einstein condensation, the extension of coherence over the entire cloud, is observed.

Spontaneous coherence in a cold exciton gas.

If bosonic particles are cooled down below the temperature of quantum degeneracy, they can spontaneously form a coherent state in which individual matter waves synchronize and combine. Spontaneous coherence of matter waves forms the basis of a number of fundamental phenomena in physics, including superconductivity, superfluidity and Bose-Einstein condensation. Spontaneous coherence is the key characteristic of condensation in momentum space. Excitons--bound pairs of electrons and holes--form a model system to explore the quantum physics of cold bosons in solids. Cold exciton gases can be realized in a system of indirect excitons, which can cool down below the temperature of quantum degeneracy owing to their long lifetimes. Here we report measurements of spontaneous coherence in a gas of indirect excitons. We found that spontaneous coherence of excitons emerges in the region of the macroscopically ordered exciton state and in the region of vortices of linear polarization. The coherence length in these regions is much larger than in a classical gas, indicating a coherent state with a much narrower than classical exciton distribution in momentum space, characteristic of a condensate. A pattern of extended spontaneous coherence is correlated with a pattern of spontaneous polarization, revealing the properties of a multicomponent coherent state. We also observed phase singularities in the coherent exciton gas. All these phenomena emerge when the exciton gas is cooled below a few kelvin.

Electrostatic conveyer for excitons.

We report on the study of indirect excitons in moving lattices-conveyers created by a set of ac voltages applied to the electrodes on the sample surface. The wavelength of this moving lattice is set by the electrode periodicity, the amplitude is controlled by the applied voltage, and the velocity is controlled by the ac frequency. We found the dynamical localization-delocalization transition for excitons in the conveyers and determined its dependence on exciton density and conveyer amplitude and velocity.

Spin transport of excitons.

We report on observation of the spin transport of spatially indirect excitons in GaAs/AlGaAs coupled quantum wells (CQW). Exciton spin transport over substantial distances, up to several micrometers in the present work, is achieved due to orders of magnitude enhancement of the exciton spin relaxation time in CQW with respect to conventional quantum wells.

High-resolution, dual-platform aCGH analysis reveals frequent HIPK2 amplification and increased expression in pilocytic astrocytomas.

Pilocytic astrocytomas (PAs, WHO grade I) are the most common brain tumors in the pediatric and adolescent population, accounting for approximately one-fifth of central nervous system tumors. Because few consistent molecular alterations have been identified in PAs compared to higher grade gliomas, we performed array comparative genomic hybridization using two independent commercial array platforms. Although whole chromosomal gains and losses were not observed, a 1-Mb amplified region of 7q34 was detected in multiple patient samples using both array platforms. Copy-number gain was confirmed in an independent tumor sample set by quantitative PCR, and this amplification was correlated to both increased mRNA and protein expression of HIPK2, a homeobox-interacting protein kinase associated with malignancy, contained within this locus. Furthermore, overexpression of wild-type HIPK2, but not a kinase-inactive mutant, in a glioma cell line conferred a growth advantage in vitro. Collectively, these results illustrate the power and necessity of implementing high-resolution, multiple-platform genomic analyses to discover small and subtle, but functionally significant, genomic alterations associated with low-grade tumor formation and growth.

Cervical cord compression from plexiform neurofibromas in neurofibromatosis 1.

Cervical cord compression from cervical root neurofibromas represents an important clinical problem in patients with neurofibromatosis type 1 (NF1), but is rarely reported. The aim of this study was to describe the clinical presentation and follow-up of children and adults with NF1 and cervical cord compression. A retrospective review of clinical records and neuroimaging studies from two large tertiary care centres between 1996 and 2006 was performed. 13 patients with NF1 and cervical cord compression were identified. Age at presentation ranged from 9 to 61 years. The most common presentation was progressive quadriparesis. 11 of 13 patients underwent cervical decompression and subtotal resection of the associated neurofibroma. The majority of patients had recovery of neurological function and no further clinical progression. Progressive neurological deficit (typically quadriparesis), rather than neuroimaging appearances, should dictate the need for surgery.

Multifocal Langerhans cell histiocytosis of the pediatric spine: a case report and literature review.

CASE REPORT: An 11-month-old boy presented with a 3-month history of lower extremity weakness. CT and MRI of the spine revealed an enhancing epidural mass, extending from T1 through T5 and exiting through multiple foramina. The largest extraspinal extent was located at the T3 vertebral level and was accompanied by complete T3 vertebral collapse. A second lytic lesion at the L2 vertebral body without an obvious enhancing mass was also noted. Open biopsy and decompression of the spinal cord were performed, and histopathological analysis revealed a mixed inflammatory lesion with abundant S-100 and CD1a immunoreactive Langerhans cells consistent with the diagnosis of Langerhans cell histiocytosis (LCH). DISCUSSION: The authors present a very rare pediatric case of spinal LCH causing spinal cord compression. Possible clues to early detection, consideration of differential diagnoses, and a brief literature review are presented.

The role of surgical biopsy in the diagnosis of glioma in individuals with neurofibromatosis-1.

Most gliomas in neurofibromatosis type 1 (NF1) are pilocytic astrocytomas (PAs) of the optic pathway occurring in young children. However, some individuals develop gliomas that lack the typical NF1-associated clinical features or radiographic appearance. We identified 17 atypical presentations from a review of 100 patients with NF1-associated gliomas. Biopsy showed that 9 were not classic PAs. These data highlight the value of biopsy in NF1-associated gliomas with unusual clinical or radiographic presentations.

Rapid enlargement of a posterior communicating artery aneurysm after Guglielmi detachable coil treatment of ipsilateral carotid artery aneurysms.

This case illustrates rapid aneurysm enlargement, presumably due to altered hemodynamics resulting from endovascular treatment of aneurysms on the same artery. We postulate that increased hemodynamic force directed to the inflow zone of the posterior communicating artery aneurysm was caused by the treatment of the two ophthalmic artery aneurysms. Originally, many of the flow vectors may have been directed into the larger ophthalmic segment aneurysm, located on the outside of the curve of the internal carotid artery. After treatment, flow may have been directed more smoothly around the carotid siphon and into the posterior communicating artery aneurysm.

Large cell/anaplastic medulloblastomas and medullomyoblastomas: clinicopathological and genetic features.

OBJECT: Medulloblastoma is the most common malignant central nervous system neoplasm found in children. A distinct variant designated large cell/anaplastic (LC/A) medulloblastoma is characterized by frequent dissemination of cerebrospinal fluid (CSF) at presentation and a more aggressive clinical course. The authors report on their examination of the clinicopathological and genetic features of seven such cases encountered at their institution. METHODS: Eighty cases of medulloblastomas were reviewed and seven (8.8%) of these were believed to fit the histological and immunohistochemical criteria for LC/A medulloblastoma. In three cases (43%) either desmoplastic or classic medulloblastoma was the underlying subtype, and in two cases (28%) the LC/A tumor was found within the setting of medullomyoblastoma. Fluorescence in situ hybridization was used in six of the seven cases to characterize the presence of isochromosome 17q, deletion of chromosome 22q (a deletion characteristically found in atypical teratoid/rhabdoid tumors), and c-myc amplification. The patients' clinical histories revealed CSF dissemination in all cases and lymph node metastasis in one case. Isochromosome 17q was found in five (83%) of six cases. Evidence of chromosomal gains indicated aneuploidy in three tumors (50%), and amplification of c-myc was found in three tumors (50%). No 22q deletions were encountered. CONCLUSIONS: A high percentage of LC/A medulloblastomas arise within a background of typical medulloblastomas or medullomyoblastomas. As is the case in conventional medulloblastomas, the presence of 17q is a common early tumorigenic event; however, in a significant percentage of specimens there is also evidence of aneuploidy and/or amplification of c-myc. These findings indicate that LC/A morphological characteristics reflect a more advanced tumor stage than that found in pure medulloblastomas or in typical medullomyoblastomas.

Bid regulation of neuronal apoptosis.

Bid is a BH3 domain only pro-apoptotic member of the Bcl-2 family which interacts with Bax to regulate apoptosis. Bax-deficient embryos show decreased neuronal programmed cell death in vivo and resistance to cytosine arabinoside (AraC)-induced neuronal apoptosis in vitro. In this report, we demonstrate that Bid-deficient embryos show no neurodevelopmental abnormalities, and Bid-deficiency has no effect on the in vitro apoptotic response of either telencephalic neural precursor cells or neurons to AraC-induced death. We conclude that bid does not play an essential role in either naturally occurring or genotoxin-induced neuronal cell death.

Neural precursor cell apoptosis and glial tumorigenesis following transplacental ethyl-nitrosourea exposure.

Neural precursor cells (NPCs) populate the embryonic ventricular zone and persist in the subependymal zone of the adult brain. We hypothesized that hereditary and/or acquired mutations in apoptosis-associated genes, such as p53 and caspases, may protect NPCs from DNA damage-induced death and predispose them to subsequent neoplastic transformation. To test this hypothesis, we exposed NPCs from wild-type and targeted gene-disrupted mouse embryos (p53, caspase-9, caspase-3, and bax mutants) to ethyl-nitrosourea (ENU), a known DNA mutagen and neural carcinogen, and measured NPC viability. We found that ENU produced caspase-3 activation and apoptotic NPC death 6-24 h after administration both in vivo and in vitro. This effect was critically dependent on p53 and caspase-9 expression. The long-term effect of intrauterine ENU exposure was examined in control and p53-deficient mice. High grade glial tumors were found in 60% of p53(-/-) young adult mice exposed to ENU on gestational day 12.5 but not in p53(+/-) or p53(+/+) littermates or in untreated p53-deficient mice. All the tumors were located supratentorially and possessed strong immunoreactivity for glial fibrillary acidic protein and the anti-apoptotic molecule Bcl-X(L). These results suggest that intrauterine exposure of NPCs to certain DNA damaging agents may synergistically interact with specific genetic abnormalities (e.g. p53 deficiency) to produce glial neoplasms in the adult brain.

DNA damage-induced neural precursor cell apoptosis requires p53 and caspase 9 but neither Bax nor caspase 3.

Programmed cell death (apoptosis) is critical for normal brain morphogenesis and may be triggered by neurotrophic factor deprivation or irreparable DNA damage. Members of the Bcl2 and caspase families regulate neuronal responsiveness to trophic factor withdrawal; however, their involvement in DNA damage-induced neuronal apoptosis is less clear. To define the molecular pathway regulating DNA damage-induced neural precursor cell apoptosis, we have examined the effects of drug and gamma-irradiation-induced DNA damage on telencephalic neural precursor cells derived from wild-type embryos and mice with targeted disruptions of apoptosis-associated genes. We found that DNA damage-induced neural precursor cell apoptosis, both in vitro and in vivo, was critically dependent on p53 and caspase 9, but neither Bax nor caspase 3 expression. Neural precursor cell apoptosis was also unaffected by targeted disruptions of Bclx and Bcl2, and unlike neurotrophic factor-deprivation-induced neuronal apoptosis, was not associated with a detectable loss of cytochrome c from mitochondria. The apoptotic pathway regulating DNA damage-induced neural precursor cell death is different from that required for normal brain morphogenesis, which involves both caspase 9 and caspase 3 but not p53, indicating that additional apoptotic stimuli regulate neural precursor cell numbers during telencephalic development.

MR imaging of herpes simplex type 1 encephalitis in infants and young children: a separate pattern of findings.

OBJECTIVE: We sought to identify the initial MR findings of herpes simplex encephalitis in infants and young children. CONCLUSION: MR imaging findings of herpes encephalitis in infants and young children appear to differ from those seen in neonates, older children, and adults. Appreciation of this MR imaging pattern coupled with a strong clinical suspicion of herpes helps to ensure the correct diagnosis is made.