Spin-Transfer Torque RAM (STTRAM) is a promising alternative to SRAMs in on-chip caches, due to several advantages, including non-volatility, low leakage, high integration density, and CMOS compatibility. However, STTRAMs' wide adoption in resource-constrained systems is impeded, in part, by high write energy and latency. A popular approach to mitigating these overheads involves relaxing the STTRAM's retention time, in order to reduce the write latency and energy. However, this approach usually requires a dynamic refresh scheme to maintain cache blocks' data integrity beyond the retention time, and typically requires an external refresh buffer. In this paper, we propose mirrorCache-an energy-efficient, buffer-free refresh scheme. MirrorCache leverages the STTRAM cell's compact feature size, and uses an auxiliary segment with the same size as the logical cache size to handle the refresh operations without the overheads of an external refresh buffer. Our experiments show that, compared to prior work, mirrorCache can reduce the average cache energy by at least 39.7% for a variety of systems.

The GMT-Consortium Large Earth Finder (G-CLEF) will be a cross-dispersed, optical band echelle spectrograph to be delivered as the first light scientific instrument for the Giant Magellan Telescope (GMT) in 2022. G-CLEF is vacuumenclosed and fiber-fed to enable precision radial velocity (PRV) measurements, especially for the detection and characterization of low-mass exoplanets orbiting solar-type stars. The passband of G-CLEF is broad, extending from 3500 angstrom to . This passband provides good sensitivity at blue wavelengths for stellar abundance studies and deep red response for observations of high-redshift phenomena. The design of G-CLEF incorporates several novel technical innovations. We give an overview of the innovative features of the current design. G-CLEF will be the first PRV spectrograph to have a composite optical bench so as to exploit that material's extremely low coefficient of thermal expansion, high in-plane thermal conductivity and high stiffness-to-mass ratio. The spectrograph camera subsystem is divided into a red and a blue channel, split by a dichroic, so there are two independent refractive spectrograph cameras. The control system software is being developed in model-driven software context that has been adopted globally by the GMT. G-CLEF has been conceived and designed within a strict systems engineering framework. As a part of this process, we have developed a analytical toolset to assess the predicted performance of G-CLEF as it has evolved through design phases.

A stable dual-wavelength Tm:Ho co-doped fiber laser operating above 2 mu m based on cascaded single mode-multimode-single mode (SMS) all-fiber structures has been proposed and experimentally demonstrated for the first time.

Recently, Regression Wavelet Analysis (RWA) was proposed as a method for lossless compression of hyperspectral images. In RWA, a linear regression is performed after a spectral wavelet transform to generate predictors which estimate the detail coefficients from approximation coefficients at each scale of the spectral wavelet transform. In this work, we propose Clustering Regression Wavelet Analysis (RWA-C), an extension of the original ‘Restricted’ RWA model which may be used to improve compression performance while maintaining component scalability. We demonstrate that clustering may be used to group pixels with similar spectral profiles, these clusters may then be more efficiently processed to improve RWA prediction performance while only requiring a modest increase side-information.

Photoconductive antenna (PCA) array based THz near-field imager incorporating Hadamard multiplexing method is developed in this work. By using a 2 × 2 dipole antenna array as the THz transmitter, the system signal-to-noise ratio (SNR) is demonstrated to be improved by a factor of 2 as the theory predicts. Additionally, a 2-D scanning of a metallic structure on a THz-transparent substrate (with a total scanning area of 1 × 1 mm2) is experimentally implemented. Correlation coefficient estimation is made afterwards to quantify the reconstructed image quality.

This paper presents a class of regular quasi-cyclic (QC) LDPC codes whose Tanner graphs have girth at least eight. These codes are constructed based on the conventional parity-check matrices of Reed-Solomon (RS) codes with minimum distance 5. Masking their parity-check matrices significantly reduces the numbers of short cycles in their Tanner graphs and results in codes which perform well over the AWGN channel in both waterfall and low error-rate regions.

We present a new method to simulate the formation of transverse modes in VECSELs. An expression for the gain as a function of carrier density and temperature is derived from a simulation of the structure reflectivity, while the field propagation in the cavity is computed with the Huygens-Fresnel integral. A rate equation model is employed to calculate the field and gain dynamics over numerous round-trips. The optimal mode size for single mode operation for a given pump shape is calculated and compared to experimental results. The effect of pump geometry, thermal lensing and structure design will be discussed.

We present a lattice QCD study of the puzzling positive-parity nucleon channel, where the Roper resonance N∗(1440) resides in experiment. The study is based on an ensemble of gauge configurations with Nf=2+1 Wilson-clover fermions with a pion mass of 156 MeV and lattice size L=2.9 fm. We use several qqq interpolating fields combined with Nπ and Nσ two-hadron operators in calculating the energy spectrum in the rest frame. Combining experimental Nπ phase shifts with elastic approximation and the Lüscher formalism suggests in the spectrum an additional energy level near the Roper mass mR=1.43 GeV for our lattice. We do not observe any such additional energy level, which implies that Nπ elastic scattering alone does not render a low-lying Roper resonance. The current status indicates that the N∗(1440) might arise as dynamically generated resonance from coupling to other channels, most notably the Nππ .

The Karhunen-Loeve Transform (KLT) is a popular transform used in multiple image processing scenarios. Sometimes, the application of the KLT is not carried out as a single transform over an entire image Rather, the image is divided into smaller spatial regions (segments), each of which is transformed by a smaller dimensional KLT. Such a situation may penalize the transform efficiency. An improvement for the segmented KLT, aiming at mitigating discontinuities arising on the edge of adjacent regions, is proposed in this paper. In the case of moderately varying image regions, discontinuities occur as the consequence of disregarded similarity between transform domains, as the order and sign of eigenvectors in the transform matrices are mismatched. In the proposed method, the KLT is adjusted to guarantee the best achievable similarity via the optimal assignment and sign correspondence for eigenvectors. Experimental results indicate that the proposed transform improves the similarity between transform domains, and reduces RMSE on the edge of adjacent regions. In consequence, images processed by the adjusted KLT present better cohesion and continuity between independently transformed regions.

Non-equilibrium multi-wavelength operation of vertical external-cavity surface-emitting lasers (VECSELs) is investigated numerically using a coupled system of Maxwell semiconductor Bloch equations. The propagation of the electromagnetic field is modeled using Maxwell's equations, and the semiconductor Bloch equations simulate the optically active quantum wells. Microscopic many-body carrier-carrier and carrier-phonon scattering are treated at the level of second Born-Markov approximation, polarization dephasing with a characteristic rate, and carrier screening with the static Lindhard formula. At first, an initialization scheme is constructed to study multi-wavelength operation in a time-resolved VECSEL. Intracavity dual-wavelength THz stabilization is examined using longitudinal modes and an intracavity etalon. In the latter, anti-correlated noise is observed for THz generation and investigated.