48 research outputs found
Assigning conservation value and identifying hotspots of endemic rattan diversity in the Western Ghats, India
Rattans, or canes, are one of the most important non-timber forest products supporting the livelihood of many forest-dwelling communities in South and North-eastern India. Due to increased demand for rattan products, rattans have been extracted indiscriminately from the Western Ghats, a 1600-km mountain chain running parallel to the west coast of India. Extensive harvesting, loss of habitat and poor regeneration has resulted in dwindling rattan populations, necessitating an urgent attempt to conserve existing rattan resources. In this study, using niche-modelling tools, an attempt has been made to identify areas of high species richness of rattans in the Western Ghats, one of the mega-diversity regions of the world. We have also developed conservation values for 21 economically important and
endemic rattans of the Western Ghats. We identified at least two to three sites of extremely high species richness outside the existing protected area network that should be prioritized for in situ conservation. This study emphasizes the need to develop strategies for the long-term conservation of rattans in the Western Ghats, Indi
ESSOP: Efficient and Scalable Stochastic Outer Product Architecture for Deep Learning
Deep neural networks (DNNs) have surpassed human-level accuracy in a variety
of cognitive tasks but at the cost of significant memory/time requirements in
DNN training. This limits their deployment in energy and memory limited
applications that require real-time learning. Matrix-vector multiplications
(MVM) and vector-vector outer product (VVOP) are the two most expensive
operations associated with the training of DNNs. Strategies to improve the
efficiency of MVM computation in hardware have been demonstrated with minimal
impact on training accuracy. However, the VVOP computation remains a relatively
less explored bottleneck even with the aforementioned strategies. Stochastic
computing (SC) has been proposed to improve the efficiency of VVOP computation
but on relatively shallow networks with bounded activation functions and
floating-point (FP) scaling of activation gradients. In this paper, we propose
ESSOP, an efficient and scalable stochastic outer product architecture based on
the SC paradigm. We introduce efficient techniques to generalize SC for weight
update computation in DNNs with the unbounded activation functions (e.g.,
ReLU), required by many state-of-the-art networks. Our architecture reduces the
computational cost by re-using random numbers and replacing certain FP
multiplication operations by bit shift scaling. We show that the ResNet-32
network with 33 convolution layers and a fully-connected layer can be trained
with ESSOP on the CIFAR-10 dataset to achieve baseline comparable accuracy.
Hardware design of ESSOP at 14nm technology node shows that, compared to a
highly pipelined FP16 multiplier design, ESSOP is 82.2% and 93.7% better in
energy and area efficiency respectively for outer product computation.Comment: 5 pages. 5 figures. Accepted at ISCAS 2020 for publicatio
Accurate deep neural network inference using computational phase-change memory
In-memory computing is a promising non-von Neumann approach for making
energy-efficient deep learning inference hardware. Crossbar arrays of resistive
memory devices can be used to encode the network weights and perform efficient
analog matrix-vector multiplications without intermediate movements of data.
However, due to device variability and noise, the network needs to be trained
in a specific way so that transferring the digitally trained weights to the
analog resistive memory devices will not result in significant loss of
accuracy. Here, we introduce a methodology to train ResNet-type convolutional
neural networks that results in no appreciable accuracy loss when transferring
weights to in-memory computing hardware based on phase-change memory (PCM). We
also propose a compensation technique that exploits the batch normalization
parameters to improve the accuracy retention over time. We achieve a
classification accuracy of 93.7% on the CIFAR-10 dataset and a top-1 accuracy
on the ImageNet benchmark of 71.6% after mapping the trained weights to PCM.
Our hardware results on CIFAR-10 with ResNet-32 demonstrate an accuracy above
93.5% retained over a one day period, where each of the 361,722 synaptic
weights of the network is programmed on just two PCM devices organized in a
differential configuration.Comment: This is a pre-print of an article accepted for publication in Nature
Communication
Mixed-precision deep learning based on computational memory
Deep neural networks (DNNs) have revolutionized the field of artificial
intelligence and have achieved unprecedented success in cognitive tasks such as
image and speech recognition. Training of large DNNs, however, is
computationally intensive and this has motivated the search for novel computing
architectures targeting this application. A computational memory unit with
nanoscale resistive memory devices organized in crossbar arrays could store the
synaptic weights in their conductance states and perform the expensive weighted
summations in place in a non-von Neumann manner. However, updating the
conductance states in a reliable manner during the weight update process is a
fundamental challenge that limits the training accuracy of such an
implementation. Here, we propose a mixed-precision architecture that combines a
computational memory unit performing the weighted summations and imprecise
conductance updates with a digital processing unit that accumulates the weight
updates in high precision. A combined hardware/software training experiment of
a multilayer perceptron based on the proposed architecture using a phase-change
memory (PCM) array achieves 97.73% test accuracy on the task of classifying
handwritten digits (based on the MNIST dataset), within 0.6% of the software
baseline. The architecture is further evaluated using accurate behavioral
models of PCM on a wide class of networks, namely convolutional neural
networks, long-short-term-memory networks, and generative-adversarial networks.
Accuracies comparable to those of floating-point implementations are achieved
without being constrained by the non-idealities associated with the PCM
devices. A system-level study demonstrates 173x improvement in energy
efficiency of the architecture when used for training a multilayer perceptron
compared with a dedicated fully digital 32-bit implementation
Theoretical insights into kesterite and stannite phases of Cu-2(Sn1-xGex)ZnSe4 based alloys: A prospective photovoltaic material
A comparative study of kesterite (KS) and stannite (ST) phases of Cu-2(Sn1-xGex)ZnSe4 (CTGZSe) alloys has been carried out using a hybrid functional within the framework of density functional theory (DFT). Our calculations suggest that KS phase is energetically more stable. We find that the total energy of the KS phase decreases with increasing concentration (x) of Ge. The calculated positive binding energies suggest that the alloy systems are stable. The formation enthalpy clearly indicates that CTGZSe alloys are thermodynamically stable and its growth can be achieved by following the route of an exothermic reaction. The calculated energy band gaps of the alloys agree well with the experimental data for the KS phase. The band offsets of KS and ST phases as a function of Ge concentration (x) can be explained on the basis of the calculated energy band gaps. We find a slight upshift in the conduction band edges while the valence band edges remain almost the same on varying the concentration (x) of Ge. Our results could be useful for the development of CTGZSe alloys based solar cells