Olga Minaeva

Chronic Traumatic Encephalopathy in Blast-Exposed Military Veterans and a Blast Neurotrauma Mouse Model

Blast exposure is associated with chronic traumatic encephalopathy, impaired neuronal function, and persistent cognitive deficits in blast-exposed military veterans and experimental animals. Blast Brain: An Invisible Injury Revealed Traumatic brain injury (TBI) is the “signature” injury of the conflicts in Afghanistan and Iraq and is associated with psychiatric symptoms and long-term cognitive disability. Recent estimates indicate that TBI may affect 20% of the 2.3 million U.S. servicemen and women deployed since 2001. Chronic traumatic encephalopathy (CTE), a tau protein–linked neurodegenerative disorder reported in athletes with multiple concussions, shares clinical features with TBI in military personnel exposed to explosive blast. However, the connection between TBI and CTE has not been explored in depth. In a new study, Goldstein et al. investigate this connection in the first case series of postmortem brains from U.S. military veterans with blast exposure and/or concussive injury. They report evidence for CTE neuropathology in the military veteran brains that is similar to that observed in the brains of young amateur American football players and a professional wrestler. The investigators developed a mouse model of blast neurotrauma that mimics typical blast conditions associated with military blast injury and discovered that blast-exposed mice also demonstrate CTE neuropathology, including tau protein hyperphosphorylation, myelinated axonopathy, microvascular damage, chronic neuroinflammation, and neurodegeneration. Surprisingly, blast-exposed mice developed CTE neuropathology within 2 weeks after exposure to a single blast. In addition, the neuropathology was accompanied by functional deficits, including slowed axonal conduction, reduced activity-dependent long-term synaptic plasticity, and impaired spatial learning and memory that persisted for 1 month after exposure to a single blast. The investigators then showed that blast winds with velocities of more than 330 miles/hour—greater than the most intense wind gust ever recorded on earth—induced oscillating head acceleration of sufficient intensity to injure the brain. The researchers then demonstrated that blast-induced learning and memory deficits in the mice were reduced by immobilizing the head during blast exposure. These findings provide a direct connection between blast TBI and CTE and indicate a primary role for blast wind–induced head acceleration in blast-related neurotrauma and its aftermath. This study also validates a new blast neurotrauma mouse model that will be useful for developing new diagnostics, therapeutics, and rehabilitative strategies for treating blast-related TBI and CTE. Blast exposure is associated with traumatic brain injury (TBI), neuropsychiatric symptoms, and long-term cognitive disability. We examined a case series of postmortem brains from U.S. military veterans exposed to blast and/or concussive injury. We found evidence of chronic traumatic encephalopathy (CTE), a tau protein–linked neurodegenerative disease, that was similar to the CTE neuropathology observed in young amateur American football players and a professional wrestler with histories of concussive injuries. We developed a blast neurotrauma mouse model that recapitulated CTE-linked neuropathology in wild-type C57BL/6 mice 2 weeks after exposure to a single blast. Blast-exposed mice demonstrated phosphorylated tauopathy, myelinated axonopathy, microvasculopathy, chronic neuroinflammation, and neurodegeneration in the absence of macroscopic tissue damage or hemorrhage. Blast exposure induced persistent hippocampal-dependent learning and memory deficits that persisted for at least 1 month and correlated with impaired axonal conduction and defective activity-dependent long-term potentiation of synaptic transmission. Intracerebral pressure recordings demonstrated that shock waves traversed the mouse brain with minimal change and without thoracic contributions. Kinematic analysis revealed blast-induced head oscillation at accelerations sufficient to cause brain injury. Head immobilization during blast exposure prevented blast-induced learning and memory deficits. The contribution of blast wind to injurious head acceleration may be a primary injury mechanism leading to blast-related TBI and CTE. These results identify common pathogenic determinants leading to CTE in blast-exposed military veterans and head-injured athletes and additionally provide mechanistic evidence linking blast exposure to persistent impairments in neurophysiological function, learning, and memory.

High-speed and high-efficiency travelling wave single-photon detectors embedded in nanophotonic circuits.

Ultrafast, high-efficiency single-photon detectors are among the most sought-after elements in modern quantum optics and quantum communication. However, imperfect modal matching and finite photon absorption rates have usually limited their maximum attainable detection efficiency. Here we demonstrate superconducting nanowire detectors atop nanophotonic waveguides, which enable a drastic increase of the absorption length for incoming photons. This allows us to achieve high on-chip single-photon detection efficiency up to 91% at telecom wavelengths, repeatable across several fabricated chips. We also observe remarkably low dark count rates without significant compromise of the on-chip detection efficiency. The detectors are fully embedded in scalable silicon photonic circuits and provide ultrashort timing jitter of 18 ps. Exploiting this high temporal resolution, we demonstrate ballistic photon transport in silicon ring resonators. Our direct implementation of a high-performance single-photon detector on chip overcomes a major barrier in integrated quantum photonics.

Concussion, microvascular injury, and early tauopathy in young athletes after impact head injury and an impact concussion mouse model

The mechanisms underpinning concussion, traumatic brain injury (TBI) and chronic traumatic encephalopathy (CTE) are poorly understood. Using neuropathological analyses of brains from teenage athletes, a new mouse model of concussive impact injury, and computational simulations, Tagge et al. show that head injuries can induce TBI and early CTE pathologies independent of concussion.

Odd- and Even-Order Dispersion Cancellation in Quantum Interferometry

We describe a novel effect involving odd-order dispersion cancellation. We demonstrate that odd- and even-order dispersion cancellation may be obtained in different regions of a single quantum interferogram using frequency-anticorrelated entangled photons and a new type of quantum interferometer. This offers new opportunities for quantum communication and metrology in dispersive media.

Precise evaluation of polarization mode dispersion by separation of even- and odd-order effects in quantum interferometry

The use of quantum correlations between photons to separate measure even- and odd-order components of polarization mode dispersion (PMD) and chromatic dispersion in discrete optical elements is investigated. Two types of apparatus are discussed which use coincidence counting of entangled photon pairs to allow sub-femtosecond resolution for measurement of both PMD and chromatic dispersion. Group delays can be measured with a resolution of order 0.1 fs, whereas attosecond resolution can be achieved for phase delays.

Submicron axial resolution in an ultrabroadband two-photon interferometer using superconducting single-photon detectors

We generate ultrabroadband biphotons via the process of spontaneous parametric down-conversion in a quasi-phase-matched nonlinear grating that has a linearly chirped poling period. Using these biphotons in conjunction with superconducting single-photon detectors (SSPDs), we measure the narrowest Hong-Ou-Mandel dip to date in a two-photon interferometer, having a full width at half maximum (FWHM) of approximately 5.7 fsec. This FWHM corresponds to a quantum optical coherence tomography (QOCT) axial resolution of 0.85 ?m. Our results indicate that a high flux of nonoverlapping biphotons may be generated, as required in many applications of nonclassical light.

Matrix of Integrated Superconducting Single-Photon Detectors With High Timing Resolution

We demonstrate a large grid of individually addressable superconducting single photon detectors on a single chip. Each detector element is fully integrated into an independent waveguide circuit with custom functionality at telecom wavelengths. High device density is achieved by fabricating the nanowire detectors in traveling wave geometry directly on top of silicon-on-insulator waveguides. Our superconducting single photon detector matrix includes detector designs optimized for high detection efficiency, low dark count rate, and high timing accuracy. As an example, we exploit the high timing resolution of a particularly short nanowire design to resolve individual photon round-trips in a cavity ring-down measurement of a silicon ring resonator.

Broadband source of polarization entangled photons.

A broadband source of polarization entangled photons based on type-II spontaneous parametric down conversion from a chirped PPKTP crystal is presented. With numerical simulation and experimental evaluation, we report a source of broadband polarization entangled states with a bandwidth of approximately 125 nm for use in quantum interferometry. The technique has the potential to become a basis for the development of flexible broadband sources with designed spectral properties.

Evaluation of polarization mode dispersion in a telecommunication wavelength selective switch using quantum interferometry

A polarization mode dispersion (PMD) measurement of a commercial telecommunication wavelength selective switch (WSS) using a quantum interferometric technique with polarization-entangled states is presented. Polarization-entangled photons with a broad spectral width covering the telecom band are produced using a chirped periodically poled nonlinear crystal. The first demonstration of a quantum metrology application using an industrial commercial device shows a promising future for practical high-resolution quantum interference.

Ultrabroadband coherence-domain imaging using parametric downconversion and superconducting single-photon detectors at 1064 nm

Coherence-domain imaging systems can be operated in a single-photon-counting mode, offering low detector noise; this in turn leads to increased sensitivity for weak light sources and weakly reflecting samples. We have demonstrated that excellent axial resolution can be obtained in a photon-counting coherence-domain imaging (CDI) system that uses light generated via spontaneous parametric downconversion (SPDC) in a chirped periodically poled stoichiometric lithium tantalate (chirped-PPSLT) structure, in conjunction with a niobium nitride superconducting single-photon detector (SSPD). The bandwidth of the light generated via SPDC, as well as the bandwidth over which the SSPD is sensitive, can extend over a wavelength region that stretches from 700 to 1500 nm. This ultrabroad wavelength band offers a near-ideal combination of deep penetration and ultrahigh axial resolution for the imaging of biological tissue. The generation of SPDC light of adjustable bandwidth in the vicinity of 1064 nm, via the use of chirped-PPSLT structures, had not been previously achieved. To demonstrate the usefulness of this technique, we construct images for a hierarchy of samples of increasing complexity: a mirror, a nitrocellulose membrane, and a biological sample comprising onion-skin cells.