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"Kyle Crowley"
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The Loud house. #1, There will be chaos
\"Learn from Lincoln Loud the ins and outs of living in a huge household with 10 sisters!\"--Back cover.
Book
Broad spectral tuning of ultra-low-loss polaritons in a van der Waals crystal by intercalation
Phonon polaritons—light coupled to lattice vibrations—in polar van der Waals crystals are promising candidates for controlling the flow of energy on the nanoscale due to their strong field confinement, anisotropic propagation and ultra-long lifetime in the picosecond range
1
–
5
. However, the lack of tunability of their narrow and material-specific spectral range—the Reststrahlen band—severely limits their technological implementation. Here, we demonstrate that intercalation of Na atoms in the van der Waals semiconductor α-V
2
O
5
enables a broad spectral shift of Reststrahlen bands, and that the phonon polaritons excited show ultra-low losses (lifetime of 4 ± 1 ps), similar to phonon polaritons in a non-intercalated crystal (lifetime of 6 ± 1 ps). We expect our intercalation method to be applicable to other van der Waals crystals, opening the door for the use of phonon polaritons in broad spectral bands in the mid-infrared domain.
The spectral range of long-lived and confined phonon polaritons in a polar van der Waals crystal is shown to be tunable by intercalation of Na atoms, expanding their potential for nanophotonic applications in the mid-infrared domain.
Journal Article
Electrical Characterization, Transport, and Doping Effects in Two-Dimensional Transition Metal Oxides
Within the past decade or so, semiconductor physics has turned a keen eye on two dimensional systems, with the pivotal investigation of atomically thin carbon films. The remarkable figures of merit produced by graphene in electronic and electrochemical applications, in contrast to bulk carbon properties, are indicative of the potential that layered materials might possess in their own right. Transition metal oxides offer a relatively unexplored facet of 2D semiconductor technology; these materials are often overlooked due to their wide band gaps when considering new subjects for nanostructure study. However, oxides offer a library of interesting properties, many of which are still not fully understood, and can be easily modified through doping to engineer new characteristics. Herein, three studies are discussed, where characterization of layered oxides, modified via various methods of doping, result in unique behaviors. The first study involves varying oxygen stoichiometry in α-MoO3, where transport is controlled by quantifiable reduction of grown α-MoO3 nanoflakes. The second details the study of LixCoO2, the staple cathode material used in lithium-ion batteries. This material exhibits unique charge-ordering phenomena as a function of lithium content, and is explored in its few-layer, single-crystal form for the first time. Finally, V2O5 is investigated, which displays p-type characteristics and a surface scattering effect when partially doped with sodium. The band structure is analyzed to explain these behaviors. The findings of these studies may play a key role in engineering thin oxide systems for future electronics applications.
Dissertation
Ultrathin 2D-oxides: a perspective on fabrication, structure, defect, transport, electron and phonon properties
In the field of atomically thin 2D materials, oxides are relatively unexplored in spite of the large number of layered oxide structures amenable to exfoliation. There is an increasing interest in ultra-thin film oxide nanostructures from applied points of view. In this perspective paper, recent progress in understanding the fundamental properties of 2D oxides is discussed. Two families of 2D oxides are considered: (1) van der Waals bonded layered materials in which the transition metal is in its highest valence state (represented by V\\(_2\\)O\\(_5\\) and MoO\\(_3\\)) and (2) layered materials with ionic bonding between positive alkali cation layers and negatively charged transition metal oxide layers (LiCoO\\(_2\\)). The chemical exfoliation process and its combinaton with mechanical exfoliation are presented for the latter. Structural phase stability of the resulting nanoflakes, the role of cation size and the importance of defects in oxides are discussed. Effects of two-dimensionality on phonons, electronic band structures and electronic screening are placed in the context of what is known on other 2D materials, such as transition metal dichalcogenides. Electronic structure is discussed at the level of many-body-perturbation theory using the quasiparticle self-consistent \\(GW\\) method, the accuracy of which is critically evaluated including effects of electron-hole interactions on screening and electron-phonon coupling. The predicted occurence of a two-dimensional electron gas on Li covered surfaces of LiCoO\\(_2\\) and its relation to topological aspects of the band structure and bonding is presented as an example of the essential role of the surface in ultrathin materials. Finally, some case studies of the electronic transport and the use of these oxides in nanoscale field effect transistors are presented.
Paper
Electron microscopy and spectroscopic study of structural changes, electronic properties and conductivity in annealed Li\\(_x\\)CoO\\(_2\\)
Chemically exfoliated nanoscale few-layer thin Li\\(_x\\)CoO\\(_2\\) samples are studied as function of annealing at various temperatures, using transmission electron microscopy (TEM) and Electron Energy Loss Spectroscopies (EELS), probing the O-K, Co-L\\(_{2,3}\\) spectra along with low energy interband transitions. These spectra are compared with first-principles DFT calculations of -Im\\([\\varepsilon^{-1}(q,\\omega)]\\) and O-2p Partial Densities of States weighted by dipole matrix elements with the core wavefunction and including the O-1s core-hole and with known trends of the L\\(_2\\)/L\\(_3\\) peak ratio to average Co valence. Trends in these spectra under the annealing procedures are established and correlated with the structural phase changes observed from diffraction TEM and High Resolution TEM images. The results are also correlated with conductivity measurements on samples subjected to the same annealing procedures. A gradual disordering of the Li and Co cations in the lattice is observed starting from a slight distortion of the pure LiCoO\\(_2\\) \\(R\\bar{3}m\\) to \\(C2/m\\) due to the lower Li content, followed by a \\(P2/m\\) phase forming at 200\\(^o\\)C indicative of Li-vacancy ordering, formation of a spinel type \\(Fd\\bar{3}m\\) phase around 250\\(^o\\)C and ultimately a rocksalt type \\(Fm\\bar{3}m\\) phase above 350\\(^o\\)C. This disordering leads to a lowering of the band gap as established by low energy EELS. The O-K spectra of the rocksalt phase are only reproduced by a calculation for pure CoO and not for a model with random distribution of Li and Co. This indicates that there may be a loss of Li from the rocksalt regions of the sample at these higher temperatures. The conductivity measurements indicate a gradual drop in conductivity above 200\\(^o\\)C, which is clearly related to the more Li-Co interdiffused phases, in which a low-spin electronic structure is no longer valid and stronger correlation effects are expected.
Paper
IRE1α–XBP1 controls T cell function in ovarian cancer by regulating mitochondrial activity
Tumours evade immune control by creating hostile microenvironments that perturb T cell metabolism and effector function
1
–
4
. However, it remains unclear how intra-tumoral T cells integrate and interpret metabolic stress signals. Here we report that ovarian cancer—an aggressive malignancy that is refractory to standard treatments and current immunotherapies
5
–
8
—induces endoplasmic reticulum stress and activates the IRE1α–XBP1 arm of the unfolded protein response
9
,
10
in T cells to control their mitochondrial respiration and anti-tumour function. In T cells isolated from specimens collected from patients with ovarian cancer, upregulation of
XBP1
was associated with decreased infiltration of T cells into tumours and with reduced
IFNG
mRNA expression. Malignant ascites fluid obtained from patients with ovarian cancer inhibited glucose uptake and caused
N
-linked protein glycosylation defects in T cells, which triggered IRE1α–XBP1 activation that suppressed mitochondrial activity and IFNγ production. Mechanistically, induction of XBP1 regulated the abundance of glutamine carriers and thus limited the influx of glutamine that is necessary to sustain mitochondrial respiration in T cells under glucose-deprived conditions. Restoring
N
-linked protein glycosylation, abrogating IRE1α–XBP1 activation or enforcing expression of glutamine transporters enhanced mitochondrial respiration in human T cells exposed to ovarian cancer ascites. XBP1-deficient T cells in the metastatic ovarian cancer milieu exhibited global transcriptional reprogramming and improved effector capacity. Accordingly, mice that bear ovarian cancer and lack XBP1 selectively in T cells demonstrate superior anti-tumour immunity, delayed malignant progression and increased overall survival. Controlling endoplasmic reticulum stress or targeting IRE1α–XBP1 signalling may help to restore the metabolic fitness and anti-tumour capacity of T cells in cancer hosts.
In human and mouse models of ovarian cancer, endoplasmic reticulum stress and the activation of the IRE1α–XBP1 pathway decreases the metabolic fitness of T cells and limits their anti-tumour functions.
Journal Article
Recommendations for the selection and treatment of patients with idiopathic intracranial hypertension for venous sinus stenting
IntroductionAlthough venous sinus stenting (VSS) has emerged as a promising treatment option for patients with idiopathic intracranial hypertension (IIH) and associated venous sinus stenosis, there is considerable ambiguity regarding patient selection criteria, treatment protocols, and management strategies.MethodsAn extensive literature review was performed to identify all reports of VSS in patients with IIH using PubMed. Recommendations for the selection and treatment of patients with IIH with VSS are outlined as determined based on author opinion from supporting studies. Due to the lack of randomized trials and few published prospective studies, standard grading scales for recommendations and level of evidence are not fully applicable and therefore a revised grading scale has been provided for recommendations.ResultsThe literature review identified a total of eight systematic reviews or meta-analyses and 29 published patient series on VSS. Recommendations for patient selection for diagnostic catheter angiography, angiography procedural considerations, stenting procedural considerations, and retreatment are provided based on the literature. Recommendations that were considered strong included: performance of venous sinus manometry to assess candidacy for treatment prior to stenting; administration of antiplatelet agents prior to stenting and for a follow-up period of at least 3–6 months; performance of post-stenting manometry to confirm resolution of pressure gradient; and performance of repeat angiography and manometry on patients with recurrence of symptoms after resolution with stenting to evaluate for recurrent stenosis.ConclusionVSS for patients with IIH with venous sinus stenosis is now an established and effective treatment option. These recommendations have been provided, based on a summative review of the available published literature, to assist in standardizing care for patients with IIH undergoing VSS.
Journal Article
International uniform response criteria for multiple myeloma
New uniform response criteria are required to adequately assess clinical outcomes in myeloma. The European Group for Blood and Bone Marrow Transplant/International Bone Marrow Transplant Registry criteria have been expanded, clarified and updated to provide a new comprehensive evaluation system. Categories for stringent complete response and very good partial response are added. The serum free light-chain assay is included to allow evaluation of patients with oligo-secretory disease. Inconsistencies in prior criteria are clarified making confirmation of response and disease progression easier to perform. Emphasis is placed upon time to event and duration of response as critical end points. The requirements necessary to use overall survival duration as the ultimate end point are discussed. It is anticipated that the International Response Criteria for multiple myeloma will be widely used in future clinical trials of myeloma.
Journal Article
Multicenter investigation of technical and clinical outcomes after thrombectomy for distal vessel occlusion by frontline technique
BackgroundEndovascular thrombectomy (EVT) is the standard-of-care for proximal large vessel occlusion (LVO) stroke. Data on technical and clinical outcomes in distal vessel occlusions (DVOs) remain limited.MethodsThis was a retrospective study of patients undergoing EVT for stroke at 32 international centers. Patients were divided into LVOs (internal carotid artery/M1/vertebrobasilar), medium vessel occlusions (M2/A1/P1) and isolated DVOs (M3/M4/A2/A3/P2/P3) and categorized by thrombectomy technique. Primary outcome was a good functional outcome (modified Rankin Scale ≤2) at 90 days. Secondary outcomes included recanalization, procedure-time, thrombectomy attempts, hemorrhage, and mortality. Multivariate logistic regressions were used to evaluate the impact of technical variables. Propensity score matching was used to compare outcome in patients with DVO treated with aspiration versus stent retrieverResultsWe included 7477 patients including 213 DVOs. Distal location did not independently predict good functional outcome at 90 days compared with proximal (p=0.467). In distal occlusions, successful recanalization was an independent predictor of good outcome (adjusted odds ratio (aOR) 5.11, p<0.05) irrespective of technique. Younger age, bridging therapy, and lower admission National Institutes of Health Stroke Scale (NIHSS) were also predictors of good outcome. Procedure time ≤1 hour or ≤3 thrombectomy attempts were independent predictors of good outcomes in DVOs irrespective of technique (aOR 4.5 and 2.3, respectively, p<0.05). There were no differences in outcomes in a DVO matched cohort of aspiration versus stent retriever. Rates of hemorrhage and good outcome showed an exponential relationship to procedural metrics, and were more dependent on time in the aspiration group and attempts in the stent retriever group.ConclusionsOutcomes following EVT for DVO are comparable to LVO with similar results between techniques. Techniques may exhibit different futility metrics; stent retriever thrombectomy was influenced by attempts whereas aspiration was more dependent on procedure time.
Journal Article