We propose an infinite-dimensional adjoint-based inexact Gauss-Newton method for the solution of inverse problems governed by Stokes models of ice sheet flow with nonlinear rheology and sliding law. The method is applied to infer the basal sliding coefficient and the rheological exponent parameter fields from surface velocities. The inverse problem is formulated as a nonlinear least-squares optimization problem whose cost functional is the misfit between surface velocity observations and model predictions. A Tikhonov regularization term is added to the cost functional to render the problem well-posed and account for observational error. Our findings show that the inexact Newton method is significantly more efficient than the nonlinear conjugate gradient method and that the number of Stokes solutions required to solve the inverse problem is insensitive to the number of inversion parameters. The results also show that the reconstructions of the basal sliding coefficient converge to the exact sliding coefficient as the observation error (here, the noise added to synthetic observations) decreases, and that a nonlinear rheology makes the reconstruction of the basal sliding coefficient more difficult. For the inversion of the rheology exponent field, we find that horizontally constant or smoothly varying parameter fields can be reconstructed satisfactorily from noisy observations.

Natural spatiotemporal processes can be highly nonstationary in many ways, e.g. the low-level non-stationarity such as spatial correlations or temporal dependencies of local pixel values; and the high-level variations such as the accumulation, deformation or dissipation of radar echoes in precipitation forecasting. From Cramér's Decomposition [4], any non-stationary process can be decomposed into deterministic, time-variant polynomials, plus a zero-mean stochastic term. By applying differencing operations appropriately, we may turn time-variant polynomials into a constant, making the deterministic component predictable.However, most previous recurrent neural networks for spatiotemporal prediction do not use the differential signals effectively, and their relatively simple state transition functions prevent them from learning too complicated variations in spacetime. We propose the Memory In Memory (MIM) networks and corresponding recurrent blocks for this purpose. The MIM blocks exploit the differential signals between adjacent recurrent states to model the non-stationary and approximately stationary properties in spatiotemporal dynamics with two cascaded, self-renewed memory modules. By stacking multiple MIM blocks, we could potentially handle higher-order non-stationarity. The MIM networks achieve the state-of-the-art results on four spatiotemporal prediction tasks across both synthetic and real-world datasets. We believe that the general idea of this work can be potentially applied to other time-series forecasting tasks.

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The recent popularity of deep neural networks (DNNs) has generated a lot of research interest in performing DNN-related computation efficiently. However, the primary focus is usually very narrow and limited to (i) inference -i.e. how to efficiently execute already trained models and (ii) image classification networks as the primary benchmark for evaluation.Our primary goal in this work is to break this myopic view by (i) proposing a new benchmark for DNN training, called TBD 1 , that uses a representative set of DNN models that cover a wide range of machine learning applications: image classification, machine translation, speech recognition, object detection, adversarial networks, reinforcement learning, and (ii) by performing an extensive performance analysis of training these different applications on three major deep learning frameworks (TensorFlow, MXNet, CNTK) across different hardware configurations (single-GPU, multi-GPU, and multi-machine). TBD currently covers six major application domains and eight different state-of-the-art models. We present a new toolchain for performance analysis for these models that combines the targeted usage of existing performance analysis tools, careful selection of new and existing metrics and methodologies to analyze the results, and utilization of domain specific characteristics of DNN training. We also build a new set of tools for memory profiling in all three major frameworks; much needed tools that can finally shed some light on precisely how much memory is consumed by different data structures (weights, activations, gradients, workspace) in DNN training. By using our tools and methodologies, we make several important observations and recommendations on where the future research and optimization of DNN training should be focused.

The purification and characterization of a novel extracellular beta-glucosidase from Paecilomyces thermophila J18 was studied. The beta-glucosidase was purified to 105-fold apparent homogeneity with a recovery yield of 21.7% by DEAE 52 and Sephacryl S-200 chromatographies. Its molecular masses were 116 and 197 kDa when detected by SDS-PAGE and gel filtration, respectively. It was a homodimeric glycoprotein with a carbohydrate content of 82.3%. The purified enzyme exhibited an optimal activity at 75 degrees C and pH 6.2. It was stable up to 65 degrees C and in the pH range of 5.0-8.5. The enzyme exhibited a broad substrate specificity and significantly hydrolyzed p-nitrophenyl-beta- d-glucopyranoside ( pNPG), cellobiose, gentiobiose, sophorose, amygdalin, salicin, daidzin, and genistin. Moreover, it displayed substantial activity on beta-glucans such as laminarin and lichenan, indicating that the enzyme has some exoglucanase activity. The rate of glucose released by the purified enzyme from cellooligosaccharides with a degree of polymerization (DP) ranging between 2 and 5 decreased with increasing chain length. Glucose and glucono-delta-lactone inhibited the beta-glucosidase competitively with Ki values of 73 and 0.49 mM, respectively. The beta-glucosidase hydrolyzed pNPG, cellobiose, gentiobiose, sophorose, salicin, and amygdalin, exhibiting apparent Km values of 0.26, 0.65, 0.77, 1.06, 1.39, and 1.45 mM, respectively. Besides, the enzyme showed transglycosylation activity, producing oligosaccharides with higher DP than the substrates when cellooligosaccharides were hydrolyzed. These properties make this beta-glucosidase useful for various biotechnological applications.

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