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The Journal of Neuroscience : the... Jun 2024During navigation, the neocortex must actively integrate learned spatial context with current sensory experience to guide behaviours. However, the relative encoding of...
During navigation, the neocortex must actively integrate learned spatial context with current sensory experience to guide behaviours. However, the relative encoding of spatial and sensorimotor information among cortical cells, and whether hippocampal feedback continues to modify these properties in familiar environments, remains poorly understood. Thus, two-photon microscopy of male and female Thy1-GCaMP6s mice was used to longitudinally image neurons spanning superficial retrosplenial cortex and layers II-Va of primary and secondary motor cortices before and after bilateral dorsal hippocampal lesions. During behaviour on a familiar cued treadmill, the locations of two added obstacles were interchanged to decouple place-tuning from cue-tuning among the position correlated cells with fields at those locations. The subpopulations of place- and cue-tuned cells each formed interareal gradients such that higher-level cortical regions exhibited higher fractions of place cells, whereas lower-level regions exhibited higher fractions of cue cells. Position correlated cells in motor cortex also formed translaminar gradients; cells closer to the cortical surface were more likely to exhibit fields and were more sparsely and precisely tuned than deeper cells. After dorsal hippocampal lesions, a neural representation of the learned environment persisted but retrosplenial cortex exhibited significantly increased cue-tuning and, in motor cortices, both position correlated cell recruitment and population activity at the unstable obstacle locations became more homogeneously elevated across laminae. Altogether, these results support that the hippocampus continues to modulate cortical responses in familiar environments, and the relative impact of top-down feedback obeys hierarchical interareal and interlaminar gradients opposite to the flow of bottom-up sensory inputs. During learning, the hippocampus imparts spatial context to memory representations throughout the superficial neocortex. However, the post-learning role of the hippocampus has not been well defined. The results of this study suggest that, during navigation of a familiar environment, the hippocampus continues to link unreliable sensory attributes to a stable contextual framework, effectively updating the learned model of the environment. The results are also consistent with top-down suppression of sensory-evoked activity during behaviour, which varied in strength according to hierarchical proximity to the hippocampus. This effect was abolished by bilateral lesions of the dorsal hippocampus, supporting that the hippocampus plays an ongoing role in propagating context-dependent predictions throughout the cortical hierarchy, a core hypothesis of the predictive coding theoretical framework.
PubMed: 38942472
DOI: 10.1523/JNEUROSCI.1619-23.2024 -
Physics in Medicine and Biology Jun 2024Conventional image quality metrics assume independence between images which is not preserved within spectral CT datasets, limiting their utility for characterizing...
Conventional image quality metrics assume independence between images which is not preserved within spectral CT datasets, limiting their utility for characterizing energy selective images. In this work, we developed a metrology to characterize energy selective images by incorporating the shared information between images within a spectral CT dataset. Approach: Signal-to-noise ratio was extended into a multivariate space where each image was treated as a separate information channel. The general definition was applied to contrast to define a multivariate contrast-to-noise ratio (CNR). The matrix contained two types of terms: a conventional CNR term, characterizing image quality within each image, and covariance weighted CNR (Covar-CNR), characterizing contrast relative to covariance between images. The metrology was demonstrated using experimental data from an investigational photon-counting CT scanner. A cylindrical water phantom containing vials of iodine and gadolinium (2, 4, 8 mg/mL) was imaged with variable tube current, tube voltage, and energy threshold. Two image series (threshold and bin images) containing two images each were defined based upon the contribution of photons to reconstructed images. Analysis of variance was calculated between CNR terms and image acquisition variables. A multivariate regression was fit to experimental data. Main Results: Bin images had a slightly higher mean and wider standard deviation (Covar-CNRlo: 3.38 ±17.25, Covar-CNRhi: 5.77±30.64) than threshold images (Covar-CNRlo: 2.08 ±1.89, Covar-CNRhi: 3.45±2.49) across all conditions. Analysis of variance found each acquisition variable had a significant relationship with both Covar-CNR terms. The multivariate regression model suggested that material concentration had the largest impact on all CNR terms. Significance: In this work, we described a theoretical framework to extend the signal-to-noise ratio to a multivariate form to characterize images independently and provide insight regarding the relationship between images. Experimental data was used to demonstrate the insight that this metrology provides about image formation factors in spectral CT. .
PubMed: 38942009
DOI: 10.1088/1361-6560/ad5d4a -
Physics in Medicine and Biology Jun 2024Proton therapy is a limited resource and is typically not available to metastatic cancer patients. Combined proton-photon therapy (CPPT), where most fractions are...
Proton therapy is a limited resource and is typically not available to metastatic cancer patients. Combined proton-photon therapy (CPPT), where most fractions are delivered with photons and only few with protons, represents an approach to distribute proton resources over a larger patient population. In this study, we consider stereotactic radiotherapy of multiple brain or liver metastases, and develop an approach to optimally take advantage of a single proton fraction by optimizing the proton and photon dose contributions to each individual metastasis. CPPT treatments must balance two competing goals: 1) deliver a larger dose in the proton fractions to reduce integral dose, and 2) fractionate the dose in the normal tissue between metastases, which requires using the photon fractions. Such CPPT treatments are generated by simultaneously optimizing IMPT and IMRT plans based on their cumulative biologically effective dose (BED). The dose contributions of the proton and photon fractions to each individual metastasis are handled as additional optimization variables in the optimization problem. The method is demonstrated for two patients with 29 and 30 brain metastases, and two patients with 4 and 3 liver metastases. Optimized CPPT plans increase the proton dose contribution to most of the metastases, while using photons to fractionate the dose around metastases which are large or located close to critical structures. On average, the optimized CPPT plans reduce the mean brain BEDby 29% and the mean liver BEDby 42% compared to IMRT-only plans. Thereby, the CPPT plans approach the dosimetric quality of IMPT-only plans, for which the mean brain BEDand mean liver BEDare reduced by 28% and 58%, respectively, compared to IMRT-only plans. CPPT with optimized proton and photon dose contributions to individual metastases may benefit selected metastatic cancer patients without tying up major proton resources. .
PubMed: 38942008
DOI: 10.1088/1361-6560/ad5d48 -
Journal of Physics. Condensed Matter :... Jun 2024The application of half-metallic materials in single-molecule optoelectronic devices opens a promising way in advancing device performance and functionality, thus...
The application of half-metallic materials in single-molecule optoelectronic devices opens a promising way in advancing device performance and functionality, thus addressing a research question of significance. Here we propose a series of single-molecule devices with half-metallic FeN4-doped armchair graphene nanoribbon as electrodes and metalloporphyrin (MPr) molecules as photoresponsive materials for photon harvesting, which are driven by photogalvanic effects (PGEs). Through the quantum transport simulations, we systematically investigated the spin-polarized photocurrents under the linearly polarized light illumination in these devices. Since the exclusive opening only exists in the spin-up channel of the half-metallic nanoribbons, these devices can generate a large photocurrent in the spin-up direction whereas suppressing the spin-down photocurrent. Consequently, they exhibit an effective spin-filtering effect at numerous photon energies. Our study unveils the excellent spin-filtering effect achieved in single-molecule optoelectronic devices with half-metallic electrodes, showing instructive significance for the future design of new optoelectronic devices. .
PubMed: 38941993
DOI: 10.1088/1361-648X/ad5d37 -
Nanotechnology Jun 2024With the increasing demand for sensing platforms operating across UV, visible, and near-infrared wavelengths, nanoporous gold has emerged as an ideal substrate for...
With the increasing demand for sensing platforms operating across UV, visible, and near-infrared wavelengths, nanoporous gold has emerged as an ideal substrate for rapid, quantitative detection of analytes with excellent specificity and high sensitivity. This study investigates thickness-mediated compositional changes and their impact on scattering characteristics of thin nanoporous gold films fabricated using selective chemical etching. Specifically, we observe thickness-induced morphological and structural changes across different fabricated samples from 25-100nm in thickness. Upon their optical characterization across UV-VIS-NIR spectral regime, we notice that the constitutional differences among samples manifest distinctively \& deterministically in their total optical scattering response. In order to gain insights into these observed scattering responses and to fathom the subtle connections between structural properties of NPG films and their optical response, a hybrid theoretical model comprising Maxwell-Garnett \& Bruggeman effective medium approximations has been adopted. Our approach not only allows to appropriately account for the inhomogeneous nature of these films, but also corroborates well with the atomic force microscopy characterizations of the fabricated samples. Furthermore, tracing such a theoretical model is important as it helps in systematically ascertaining additional loss terms emerging in the complex dielectric function of films due to their nanoscale porosity \& roughness, permitting a good reproduction of measured optical spectra. We believe, our approach will not only facilitate accurate regulation of losses in NPG thin films but will also aid in deriving customized optical performance from them, thereby advancing their potential applications in sensing and beyond.
PubMed: 38941980
DOI: 10.1088/1361-6528/ad5cfa -
Scientific Reports Jun 2024Adam's Bridge is a submerged ridge connecting India and Sri Lanka, generally regarded as a chain of shoals extending for ~ 29 km from Dhanushkodi on the Indian side...
Adam's Bridge is a submerged ridge connecting India and Sri Lanka, generally regarded as a chain of shoals extending for ~ 29 km from Dhanushkodi on the Indian side to Talaimannar Island of Sri Lanka. A high-resolution digital bathymetric elevation model generated using the seafloor returned photons of ICESat-2 was used to understand the intricate details of Adam's Bridge structure. Photons emanating from ICESat-2's green laser have the potential to detect the seafloor up to a depth of ~ 40 m; taking a cue from this potentiality, in our research, we have accrued ~ 0.2 million photons representing the depth information and generated a 10 m resolution bathymetric data for the extent of Adam's Bridge. Visual interpretations made from this bathymetric data through 3D perspectives with multi-directional lighting effects, and also with the derived parameters like contours, slope, and volumetric analysis, enabled us to recognize the current form of Adam's Bridge's physical features. The results from our research confirm that, in its entirety, Adam's Bridge is a submarine continuation of Dhanushkodi and Talaimannar Island. Throughout the crest line of Adam's Bridge, approximately 1.5 km on either side is highly undulating within the super-shallow water with occurrences of sudden depths. There is an asymmetry of transverse slopes to the base on both sides of Adam's Bridge, indicating dominant transgression of material energy from the waters of the Gulf of Mannar compared to the Palk Strait. The volume of Adam's Bridge computed in our research yielded a value of ~ 1 km; interestingly, only 0.02 percent of this volume is above the mean sea level, and in general, the same is visible in optical satellite imagery-in total ~ 99.98 percent of the Adam's Bridge is submerged in shallow and super-shallow waters.
PubMed: 38942892
DOI: 10.1038/s41598-024-65908-2 -
Nature Communications Jun 2024The tunable properties of halide perovskite/two dimensional (2D) semiconductor mixed-dimensional van der Waals heterostructures offer high flexibility for innovating...
The tunable properties of halide perovskite/two dimensional (2D) semiconductor mixed-dimensional van der Waals heterostructures offer high flexibility for innovating optoelectronic and photonic devices. However, the general and robust growth of high-quality monocrystalline halide perovskite/2D semiconductor heterostructures with attractive optical properties has remained challenging. Here, we demonstrate a universal van der Waals heteroepitaxy strategy to synthesize a library of facet-specific single-crystalline halide perovskite/2D semiconductor (multi)heterostructures. The obtained heterostructures can be broadly tailored by selecting the coupling layer of interest, and can include perovskites varying from all-inorganic to organic-inorganic hybrid counterparts, individual transition metal dichalcogenides or 2D heterojunctions. The CsPbIBr/WSe heterostructures demonstrate ultrahigh optical gain coefficient, reduced gain threshold and prolonged gain lifetime, which are attributed to the reduced energetic disorder. Accordingly, the self-organized halide perovskite/2D semiconductor heterostructure lasers show highly reproducible single-mode lasing with largely reduced lasing threshold and improved stability. Our findings provide a high-quality and versatile material platform for probing unique optoelectronic and photonic physics and developing further electrically driven on-chip lasers, nanophotonic devices and electronic-photonic integrated systems.
PubMed: 38942769
DOI: 10.1038/s41467-024-49364-0 -
Inorganic Chemistry Jun 2024Both metalloporphyrins and heterometallic {CrNi} rings are of significant research interest due to their proposed roles in quantum information processing devices. In...
Both metalloporphyrins and heterometallic {CrNi} rings are of significant research interest due to their proposed roles in quantum information processing devices. In this study, we present a series of complexes in which [CrNiF(Etglu)(OCBu)] (-EtgluH = -ethyl-dglucamine) heterometallic rings are coordinated to metalloporphyrin linkers: the symmetric [M(TPyP)] for M = Cu, VO, and HTPyP = 5,10,15,20-tetra(4-pyridyl)porphyrin; and the asymmetric [{VO}(TrPPyP)] for H(TrPPyP) = 5,10,15-(triphenyl)-20-(4-pyridyl)porphyrin. The magnetic interactions present in these complexes are unraveled using the continuous wave (CW) electron paramagnetic resonance (EPR) technique. The nature of the coupling between the {CrNi} rings and the central metalloporphyrin is assessed by numerical simulations of CW EPR spectra and determined to be on the order of 0.01 cm, larger than the dipolar ones and suitable for individual spin addressability in multiqubit architectures.
PubMed: 38941532
DOI: 10.1021/acs.inorgchem.4c01248 -
Annual Review of Physical Chemistry Jun 2024The ability of nanophotonic cavities to confine and store light to nanoscale dimensions has important implications for enhancing molecular, excitonic, phononic, and... (Review)
Review
The ability of nanophotonic cavities to confine and store light to nanoscale dimensions has important implications for enhancing molecular, excitonic, phononic, and plasmonic optical responses. Spectroscopic signatures of processes that are ordinarily exceedingly weak such as pure absorption and Raman scattering have been brought to the single-particle limit of detection, while new emergent polaritonic states of optical matter have been realized through coupling material and photonic cavity degrees of freedom across a wide range of experimentally accessible interaction strengths. In this review, we discuss both optical and electron beam spectroscopies of cavity-coupled material systems in weak, strong, and ultrastrong coupling regimes, providing a theoretical basis for understanding the physics inherent to each while highlighting recent experimental advances and exciting future directions.
PubMed: 38941525
DOI: 10.1146/annurev-physchem-083122-125525 -
Angewandte Chemie (International Ed. in... Jun 2024Near-infrared light-driven photocatalytic CO2 reduction (NIR-CO2PR) holds tremendous promise for the production of valuable commodity chemicals and fuels. However,...
Near-infrared light-driven photocatalytic CO2 reduction (NIR-CO2PR) holds tremendous promise for the production of valuable commodity chemicals and fuels. However, designing photocatalysts capable of reducing CO2 with low energy NIR photons remains challenging. Herein, a novel NIR-driven photocatalyst comprising an anionic Ru complex intercalated between NiAl-layered double hydroxide nanosheets (NiAl-Ru-LDH) is shown to deliver efficient CO2 photoreduction (0.887 μmol h-1) with CO selectivity of 84.81% under 1200 nm illumination and excellent stability over 50 testing cycles. This remarkable performance results from the intercalated Ru complex lowering the LDH band gap (0.98 eV) via a compression-related charge redistribution phenomenon. Furthermore, transient absorption spectroscopy data verified light-induced electron transfer from the Ru complex towards the LDH sheets, increasing the availability of electrons to drive CO2PR. The presence of hydroxyl defects in the LDH sheets promotes the adsorption of CO2 molecules and lowers the energy barriers for NIR-CO2PR to CO. To our knowledge, this is one of the first reports of NIR-CO2PR at wavelengths up to 1200 nm in LDH-based photocatalyst systems.
PubMed: 38941107
DOI: 10.1002/anie.202407638