Optical investigation of many-body interactions in transition metal dichalcogenide heterostructures

Two-dimensional transition metal dichalcogenide (TMD) heterostructures have emerged as a novel platform for the investigation of many-body physical phenomena. In these systems, tightly bound excitons dressed by a gate-tunable Fermi sea form exciton-polarons, which are sensitive to Coulomb and spin interactions. In addition, TMD moir´e devices provide a highly tunable platform to study strongly correlated electronic states. This thesis describes the use of magneto-optical polarisation-resolved white-light confocal reflection spectroscopy at cryogenic temperatures (4 K) to probe different many-body interactions in TMD heterostructure devices. First, monolayer and bilayer tungsten diselenide (WSe2) and molybdenum diselenide (MoSe2) are investigated under varying carrier concentration. The doping dependent dispersions of the exciton-polarons are shown to be excellent probes of the distinctive band structures of these materials. Then, in a moir´e heterobilayer MoSe2/WSe2 structure, optically injected excitons are shown to interact with itinerant carriers occupying narrow moir´e bands to form exciton-polarons sensitive to strong correlations. At a multitude of fractional fillings of the moir´e lattice, the ordering of both electrons and holes into stable correlated electronic states is observed, leading to extraordinary Zeeman splittings of the exciton-polarons. Next, in heterotrilayer bilayer WSe2/monolayer MoSe2, the energetic ordering of the moir´e bands is shown to be highly tunable with applied vertical electric field, leading to the demonstration of hole transfer between correlated states in K and Γ valley derived moir´e bands. Finally, the moire lattice uniformity of MoSe2/WSe2 moir´e heterostructures is probed by spatial mapping of the electronic correlations, leading to a measured variation in twist angle of 0.6 degrees across the device. These results establish WSe2 and MoSe2 heterostructures as an exciting platform for investigations of exciton-polarons, Fermi-Hubbard or Bose-Hubbard physics

The RAVE Network Attack

Cyber-attacks are an ever-present threat to our modern, technologically dependent world. This looming shadow of a disaster waiting to happen has led companies to invest heavily into their software resiliency and network defenses. However, many companies, especially small ones, have forgotten the danger of an insider threat, or at least how an insider threat could be emulated. Anything on the inside of a network automatically has a higher level of trust because most companies’ defenses have only gone as far as to protect their perimeter and educate their employees. What if an outside attacker was able to gain physical access for just a brief time to the inside of a small business? Say, in a waiting room or consultation? RAVE stands for Remote Attack Vector Engine, and is a device designed to test this flaw. RAVE is a small Raspberry Pi 0, disguised as any common workplace device, that an attacker can plant in a business’s network to attack from the inside. By connecting RAVE to an internal ethernet port, a secure reverse OpenVPN connection is automatically created to a Middleman Server over common HTTPS traffic through port 443 and kept persistent. An operator is then able to connect into RAVE through the Middleman Server. The operator can then use tools installed on the device to launch network scans, perform brute force password attacks on network devices and services, take over more devices on the network, and steal data from the company. By using this device, penetration testers can help companies develop better security practices to keep their network safe from infiltration and exploitation

Concussion and the Severity of Head Impacts in Mixed Martial Arts

Background: Concern about the consequences of head impacts in US football motivated researchers to investigate and develop instrumentation to measure the severity of these impacts. However, the severity of head impacts in unhelmeted sports is largely unknown as miniaturised sensor technology has only recently made it possible to measure these impacts in vivo. Aim: The objective of this study was to measure the linear and angular head accelerations in impacts in mixed martial arts (MMA), and correlate these with concussive injuries. Methods: Thirteen MMA fighters were fitted with the Stanford instrumented mouthguard (MiG2.0). The mouthguard records linear acceleration and angular velocity in 6 degrees of freedom. Angular acceleration was calculated by differentiation. All events were video recorded, time stamped and reported impacts confirmed. Results: 451 verified head impacts above 10g were recorded during 19 sparring events (n=298) and 11 competitive events (n=153). The average resultant linear acceleration was 38.0g ± 24.3g while the average resultant angular acceleration was 2567 ± 1739rad/s2. The competitive bouts resulted in five concussions being diagnosed by a medical doctor. The average resultant acceleration (of the impact with the highest angular acceleration) in these bouts was 86.7 ± 18.7g and 7561 ± 3438rads/s2. The average maximum Head Impact Power (HIP) was 20.6kW in the case of concussion and 7.15kW for the uninjured athletes. Conclusion: The study recorded novel data for sub-concussive and concussive impacts. Events that resulted in a concussion had an average maximum angular acceleration that was 24.7% higher and an average maximum HIP that was 189% higher than events where there was no injury. The findings are significant in understanding the human tolerance to short-duration, high linear and angular accelerations

Spin–layer locking of interlayer excitons trapped in moiré potentials

Van der Waals heterostructures offer attractive opportunities to design quantum materials. For instance, transition metal dichalcogenides (TMDs) possess three quantum degrees of freedom: spin, valley index, and layer index. Further, twisted TMD heterobilayers can form moir\'e patterns that modulate the electronic band structure according to atomic registry, leading to spatial confinement of interlayer exciton (IXs). Here we report the observation of spin-layer locking of IXs trapped in moir\'e potentials formed in a heterostructure of bilayer 2H-MoSe$_2$ and monolayer WSe$_2$. The phenomenon of locked electron spin and layer index leads to two quantum-confined IX species with distinct spin-layer-valley configurations. Furthermore, we observe that the atomic registries of the moir\'e trapping sites in the three layers are intrinsically locked together due to the 2H-type stacking characteristic of bilayer TMDs. These results identify the layer index as a useful degree of freedom to engineer tunable few-level quantum systems in two-dimensional heterostructures.Comment: 10 pages, 4 figures. Supplementary Material available at: https://www.dropbox.com/s/8331cfoasdofwkq/Brotons-Gisbert_Suppl_Info.pdf?dl=

Spatiotemporal progression of ubiquitin-proteasome system inhibition after status epilepticus suggests protective adaptation against hippocampal injury.

BACKGROUND: The ubiquitin-proteasome-system (UPS) is the major intracellular pathway leading to the degradation of unwanted and/or misfolded soluble proteins. This includes proteins regulating cellular survival, synaptic plasticity and neurotransmitter signaling; processes controlling excitability thresholds that are altered by epileptogenic insults. Dysfunction of the UPS has been reported to occur in a brain region- and cell-specific manner and contribute to disease progression in acute and chronic brain diseases. Prolonged seizures, status epilepticus, may alter UPS function but there has been no systematic attempt to map when and where this occurs in vivo or to determine the consequences of proteasome inhibition on seizure-induced brain injury. METHOD: To determine whether seizures lead to an impairment of the UPS, we used a mouse model of status epilepticus whereby seizures are triggered by an intra-amygdala injection of kainic acid. Status epilepticus in this model causes cell death in selected brain areas, in particular the ipsilateral CA3 subfield of the hippocampus, and the development of epilepsy after a short latent period. To monitor seizure-induced dysfunction of the UPS we used a UPS inhibition reporter mouse expressing the ubiquitin fusion degradation substrate ubiquitin(G76V)-green fluorescent protein. Treatment with the specific proteasome inhibitor epoxomicin was used to establish the impact of proteasome inhibition on seizure-induced pathology. RESULTS AND CONCLUSIONS: Our studies show that status epilepticus induced by intra-amygdala kainic acid causes select spatio-temporal UPS inhibition which is most evident in damage-resistant regions of the hippocampus, including CA1 pyramidal and dentate granule neurons then appears later in astrocytes. In support of this exerting a beneficial effect, injection of mice with the proteasome inhibitor epoxomicin protected the normally vulnerable hippocampal CA3 subfield from seizure-induced neuronal death in the model. These studies reveal brain region- and cell-specific UPS impairment occurs after seizures and suggest UPS inhibition can protect against seizure-induced brain damage. Identifying networks or pathways regulated through the proteasome after seizures may yield novel target genes for the treatment of seizure-induced cell death and possibly epilepsy

Dynamic Blood-Brain Barrier Regulation in Mild Traumatic Brain Injury

Whereas the diagnosis of moderate and severe traumatic brain injury (TBI) is readily visible on current medical imaging paradigms (magnetic resonance imaging [MRI] and computed tomography [CT] scanning), a far greater challenge is associated with the diagnosis and subsequent management of mild TBI (mTBI), especially concussion which, by definition, is characterized by a normal CT. To investigate whether the integrity of the blood-brain barrier (BBB) is altered in a high-risk population for concussions, we studied professional mixed martial arts (MMA) fighters and adolescent rugby players. Additionally, we performed the linear regression between the BBB disruption defined by increased gadolinium contrast extravasation on dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) on MRI and multiple biomechanical parameters indicating the severity of impacts recorded using instrumented mouthguards in professional MMA fighters. MMA fighters were examined pre-fight for a baseline and again within 120 h post-competitive fight, whereas rugby players were examined pre-season and again post-season or post-match in a subset of cases. DCE-MRI, serological analysis of BBB biomarkers, and an analysis of instrumented mouthguard data, was performed. Here, we provide pilot data that demonstrate disruption of the BBB in both professional MMA fighters and rugby players, dependent on the level of exposure. Our data suggest that biomechanical forces in professional MMA and adolescent rugby can lead to BBB disruption. These changes on imaging may serve as a biomarker of exposure of the brain to repetitive subconcussive forces and mTBI

Age and gender differences in narcissism: A comprehensive study across eight measures and over 250,000 participants

Age and gender differences in narcissism have been studied often. However, considering the rich history of narcissism research accompanied by its diverging conceptualizations, little is known about age and gender differences across various narcissism measures. The present study investigated age and gender differences and their interactions across eight widely used narcissism instruments (i.e., Narcissistic Personality Inventory, Hypersensitive Narcissism Scale, Dirty Dozen, Psychological Entitlement Scale, Narcissistic Personality Disorder Symptoms from the Diagnostic and Statistical Manual of Mental Disorders, Version IV, Narcissistic Admiration and Rivalry Questionnaire-Short Form, Single-Item Narcissism Scale, and brief version of the Pathological Narcissism Inventory). The findings of Study 1 (N = 5,736) revealed heterogeneity in how strongly the measures are correlated. Some instruments loaded clearly on one of the three factors proposed by previous research (i.e., Neuroticism, Extraversion, Antagonism), while others cross-loaded across factors and in distinct ways. Cross-sectional analyses using each measure and meta-analytic results across all measures (Study 2) with a total sample of 270,029 participants suggest consistent linear age effects (random effects meta-analytic effect of r = -.104), with narcissism being highest in young adulthood. Consistent gender differences also emerged (random effects meta-analytic effect was -.079), such that men scored higher in narcissism than women. Quadratic age effects and Age × Gender effects were generally very small and inconsistent. We conclude that despite the various conceptualizations of narcissism, age and gender differences are generalizable across the eight measures used in the present study. However, their size varied based on the instrument used. We discuss the sources of this heterogeneity and the potential mechanisms for age and gender differences

Effects of antiplatelet therapy on stroke risk by brain imaging features of intracerebral haemorrhage and cerebral small vessel diseases: subgroup analyses of the RESTART randomised, open-label trial

Background Findings from the RESTART trial suggest that starting antiplatelet therapy might reduce the risk of recurrent symptomatic intracerebral haemorrhage compared with avoiding antiplatelet therapy. Brain imaging features of intracerebral haemorrhage and cerebral small vessel diseases (such as cerebral microbleeds) are associated with greater risks of recurrent intracerebral haemorrhage. We did subgroup analyses of the RESTART trial to explore whether these brain imaging features modify the effects of antiplatelet therapy

The origin of iron silicides in ureilite meteorites

Ureilite meteorites contain iron silicide minerals including suessite (Fe,Ni)3Si, hapkeite (Fe2Si) and xifengite (Fe5Si3). Despite occurring mostly in brecciated varieties presumed to be derived from the regolith of the ureilite parent asteroid, suessite has also been confirmed in one lithology of a dimict ureilite (NWA 1241). In contrast, Si-bearing Fe-metals occur in both brecciated and unbrecciated ureilites, implying that they were formed throughout the ureilite parent asteroid. We examined major, minor and trace element data of Fe-metals in seven brecciated ureilites (DaG 319, DaG 999, DaG 1000, DaG 1023, DaG 1047, EET 83309, and EET 87720) in addition to the dimict ureilite NWA 1241. In this study we show that the silicides and Si-bearing metals in ureilites have similar siderophile trace element patterns; therefore, the precursors to the silicides were indigenous to the ureilite parent body. Si-free kamacite grains in brecciated ureilites show flatter, more chondritic siderophile element patterns. They may also be derived from the interior of the ureilite parent body, but some may be of exogenous origin (impactor debris), as are rare taenite grains. On Earth, iron silicides are often formed under high-temperature and strongly reducing conditions (e.g. blast furnaces, lightning strikes). On the Moon, hapkeite (Fe2Si) and other silicides have been found in the regolith where they were formed by impact-induced space weathering. In the Stardust aerogel, iron silicides derived from comet Wild2 were also formed by an impact-related reduction process. Silicides in ureilite regolith breccias may have formed by similar processes but ureilites additionally contain abundant elemental carbon which probably acted as a reducing agent, thus larger and more abundant silicide grains were formed than in the lunar regolith or cometary material. The origin of suessite in NWA 1241 may be analogous to that of reduced lithologies in the terrestrial mantle, although a regolith origin may also be possible since this sample is shown here to be a dimict breccia