Sparse Representation of Brain Aging: Extracting Covariance Patterns from Structural MRI

An enhanced understanding of how normal aging alters brain structure is urgently needed for the early diagnosis and treatment of age-related mental diseases. Structural magnetic resonance imaging (MRI) is a reliable technique used to detect age-related changes in the human brain. Currently, multivariate pattern analysis (MVPA) enables the exploration of subtle and distributed changes of data obtained from structural MRI images. In this study, a new MVPA approach based on sparse representation has been employed to investigate the anatomical covariance patterns of normal aging. Two groups of participants (group 1∶290 participants; group 2∶56 participants) were evaluated in this study. These two groups were scanned with two 1.5 T MRI machines. In the first group, we obtained the discriminative patterns using a t-test filter and sparse representation step. We were able to distinguish the young from old cohort with a very high accuracy using only a few voxels of the discriminative patterns (group 1∶98.4%; group 2∶96.4%). The experimental results showed that the selected voxels may be categorized into two components according to the two steps in the proposed method. The first component focuses on the precentral and postcentral gyri, and the caudate nucleus, which play an important role in sensorimotor tasks. The strongest volume reduction with age was observed in these clusters. The second component is mainly distributed over the cerebellum, thalamus, and right inferior frontal gyrus. These regions are not only critical nodes of the sensorimotor circuitry but also the cognitive circuitry although their volume shows a relative resilience against aging. Considering the voxels selection procedure, we suggest that the aging of the sensorimotor and cognitive brain regions identified in this study has a covarying relationship with each other

Morphological diversity of single neurons in molecularly defined cell types.

Dendritic and axonal morphology reflects the input and output of neurons and is a defining feature of neuronal types1,2, yet our knowledge of its diversity remains limited. Here, to systematically examine complete single-neuron morphologies on a brain-wide scale, we established a pipeline encompassing sparse labelling, whole-brain imaging, reconstruction, registration and analysis. We fully reconstructed 1,741 neurons from cortex, claustrum, thalamus, striatum and other brain regions in mice. We identified 11 major projection neuron types with distinct morphological features and corresponding transcriptomic identities. Extensive projectional diversity was found within each of these major types, on the basis of which some types were clustered into more refined subtypes. This diversity follows a set of generalizable principles that govern long-range axonal projections at different levels, including molecular correspondence, divergent or convergent projection, axon termination pattern, regional specificity, topography, and individual cell variability. Although clear concordance with transcriptomic profiles is evident at the level of major projection type, fine-grained morphological diversity often does not readily correlate with transcriptomic subtypes derived from unsupervised clustering, highlighting the need for single-cell cross-modality studies. Overall, our study demonstrates the crucial need for quantitative description of complete single-cell anatomy in cell-type classification, as single-cell morphological diversity reveals a plethora of ways in which different cell types and their individual members may contribute to the configuration and function of their respective circuits

Modelling band-to-band tunneling current in InP-based heterostructure photonic devices

Some semiconductor photonic devices show large discontinuities in the band structure. Short tunnel paths caused by this band structure may lead to an excessive tunneling current, especially in highly doped layers. Modelling of this tunnelling current is therefore important when designing photonic devices with such band structures. The traditional Kane’s tunnelling model can only be applied to homostructures. An extension to heterostructures is developed to study interband tunneling probability in InP-based heterostructures and the resulting tunnelling current is calculated

200 Gbps OOK transmission over an indoor optical wireless link enabled by an integrated cascaded aperture optical receiver

\u3cp\u3eEnabled by an integrated InP membrane cascaded aperture optical receiver with flexibly-designed light collection aperture and >67 GHz bandwidth, the record-breaking 200 Gbps (5λ×40 Gbps) OOK data transmission is achieved over a 2 meter indoor optical wireless link.\u3c/p\u3

Ultra-sharp and highly tolerant waveguide bends for InP photonic membrane circuits

In this paper we present a sharp bend design for the InP-based photonic membrane, which shows low loss and high tolerance. The traditional arc bends on InP membranes face high loss when the bending radii reduce below 2 µm. And their performance deteriorates even more dramatically at the presence of waveguide footings. The proposed design has advantages of low loss, high compactness, wide spectral response and ease of fabrication. It is also verified to be much more resilient to design and fabrication variations, such as waveguide footings. The sharp bend is fabricated together with traditional arc bends. Experimental results confirm its potential as a basic building block for InP photonic membrane platforms

Membrane-based receiver/transmitter for reconfigurable optical wireless beam-steering systems

In this paper, a novel integrated optical wireless receiver/transmitter is presented. The device is realized on an InP membrane platform where active and passive components are integrated monolithically. It can be reconfigured to either receiver mode or transmitter mode, by simple control on the operation mode of a photodetector (short SOA). Demonstration of the receiver mode in an indoor optical wireless system has shown 17.4-Gbps OFDM signal transmission, illustrating the potential of this concept

A novel optically wide-band electro-absorption modulator based on bandfilling in n-InGaAs

We propose a novel membrane electro-absorption modulator (EAM) integrated on silicon. The device is based on the carrier-concentration dependent absorption of highly-doped n-InGaAs. The modulator is predicted to be wide-band and to provide an extinction ratio (ER) of 7.5 dB, an insertion loss (IL) of 1.1 dB, a modulation speed above 10 Gbit/s and a power consumption of 80 fJ/bit. The modulator has a small footprint of 10 x 120 μm² and operates with a 1.5 V voltage swing