SPMS Journal Articles
http://hdl.handle.net/10220/64
Tue, 11 Dec 2018 19:47:45 GMT2018-12-11T19:47:45ZSpectroscopic characterization and mechanistic studies on visible light photoredox carbon–carbon bond formation by bis(arylimino)acenaphthene copper photosensitizers
http://hdl.handle.net/10220/46916
Spectroscopic characterization and mechanistic studies on visible light photoredox carbon–carbon bond formation by bis(arylimino)acenaphthene copper photosensitizers
Ng, Yik Yie; Tan, Lisa Jiaying; Ng, Shue Mei; Chai, Yoke Tin; Ganguly, Rakesh; Du, Yonghua; Yeow, Edwin Kok Lee; Soo, Han Sen
Currently, the most popular molecular photosensitizers used for synthetic organic chemistry and energy applications are still the noble metal-based ruthenium and iridium complexes that usually require expensive metal and ligand precursors. In contrast, bis(arylimino)acenaphthene (Ar-BIAN) are established redox non-innocent π-accepting ligands that are easily assembled in one condensation step from affordable and commercially available precursors. Herein, we have developed a series of Ar-BIAN Cu(I) complexes as visible light harvesting photosensitizers. Notably, one of these panchromatic, homoleptic Ar-BIAN Cu(I) complexes exhibits a radiative recombination lifetime that is longer than diffusion control, as observed by time-correlated single photon counting spectroscopy. The Ar-BIAN Cu(I) facilitates visible-light promoted atom transfer radical addition reactions via carbon-carbon bond formation with CBr3 radicals in good yields of up to 75%. Steady-state and transient absorption spectroscopic measurements, together with spectroelectrochemical experiments and intermediate isolation studies, were performed to obtain insights into this photoredox catalysis and provide guidelines for the general deployment of Ar-BIAN Cu(I) photosensitizers in synthetic organic chemistry and renewable energy applications.
Mon, 01 Jan 2018 00:00:00 GMThttp://hdl.handle.net/10220/469162018-01-01T00:00:00ZEmbeddings of Schatten norms with applications to data streams
http://hdl.handle.net/10220/46888
Embeddings of Schatten norms with applications to data streams
Li, Yi; Woodruff, David P.
Given an n×d matrix A, its Schatten-p norm, p >= 1, is defined as |A|_p = (sum_{i=1}^rank(A) sigma(i)^p）^{1/p} where sigma_i(A) is the i-th largest singular value of A. These norms have been studied in functional analysis in the context of non-commutative L_p-spaces, and recently in data stream and linear sketching models of computation. Basic questions on the relations between these norms, such as their embeddability, are still open. Specifically, given a set of matrices A_1, ... , A_poly(nd) in R^{n x d}, suppose we want to construct a linear map L such that L(A_i) in R^{n' x d'} for each i, where n' < n and d' < d, and further, |A_i|p <= |L(A_i)|_q <= D_{p,q}|A_i|_p for a given approximation factor D_{p,q} and real number q >= 1. Then how large do n' and d' need to be as a function of D_{p,q}? We nearly resolve this question for every p, q greater than or equal to 1, for the case where L(A_i) can be expressed as R*A_i*S, where R and S are arbitrary matrices that are allowed to depend on A_1, ... ,A_t, that is, L(A_i) can be implemented by left and right matrix multiplication. Namely, for every p, q greater than or equal to 1, we provide nearly matching upper and lower bounds on the size of n' and d' as a function of D_{p,q}. Importantly, our upper bounds are oblivious, meaning that R and S do not depend on the A_i, while our lower bounds hold even if R and S depend on the A_i. As an application of our upper bounds, we answer a recent open question of Blasiok et al. about space-approximation trade-offs for the Schatten 1-norm, showing in a data stream it is possible to estimate the Schatten-1 norm up to a factor of D greater than or equal to 1 using O~(min(n, d)^2/D^4) space.
Sun, 01 Jan 2017 00:00:00 GMThttp://hdl.handle.net/10220/468882017-01-01T00:00:00ZCorrelation in hard distributions in communication complexity
http://hdl.handle.net/10220/46886
Correlation in hard distributions in communication complexity
Bottesch, Ralph Christian; Gavinsky, Dmitry; Klauck, Hartmut
We study the effect that the amount of correlation in a bipartite distribution has on the communication complexity of a problem under that distribution. We introduce a new family of complexity measures that interpolates between the two previously studied extreme cases: the (standard) randomised communication complexity and the case of distributional complexity under product distributions. - We give a tight characterisation of the randomised complexity of Disjointness under distributions with mutual information k, showing that it is Theta(sqrt(n(k+1))) for all 0 <= k <= n. This smoothly interpolates between the lower bounds of Babai, Frankl and Simon for the product distribution case [k=0], and the bound of Razborov for the randomised case. The upper bounds improve and generalise what was known for product distributions, and imply that any tight bound for Disjointness needs Omega(n) bits of mutual information in the corresponding distribution. - We study the same question in the distributional quantum setting, and show a lower bound of Omega((n(k+1))^{1/4}), and an upper bound (via constructing communication protocols), matching up to a logarithmic factor. - We show that there are total Boolean functions f_d that have distributional communication complexity O(log(n)) under all distributions of information up to o(n), while the (interactive) distributional complexity maximised over all distributions is Theta(log(d)) for n <= d <= 2^{n/100}. This shows, in particular, that the correlation needed to show that a problem is hard can be much larger than the communication complexity of the problem. - We show that in the setting of one-way communication under product distributions, the dependence of communication cost on the allowed error epsilon is multiplicative in log(1/epsilon) - the previous upper bounds had the dependence of more than 1/epsilon. This result, for the first time, explains how one-way communication complexity under product distributions is stronger than PAC-learning: both tasks are characterised by the VC-dimension, but have very different error dependence (learning from examples, it costs more to reduce the error).
Thu, 01 Jan 2015 00:00:00 GMThttp://hdl.handle.net/10220/468862015-01-01T00:00:00ZUltrastrong light-matter coupling of cyclotron transition in monolayer MoS2
http://hdl.handle.net/10220/46885
Ultrastrong light-matter coupling of cyclotron transition in monolayer MoS2
Li, Benliang; Liu, Tao; Hewak, Daniel W.; Shen, Zexiang; Wang, Qi Jie
The light-matter coupling between cyclotron transition and photon is theoretically investigated in a monolayer MoS2 system with consideration of the influence of electron-hole asymmetry. The results show that ultrastrong light-matter coupling can be achieved at a high filling factor of Landau levels. Furthermore, we show that, in contrast to the case for conventional semiconductor resonators, the MoS2 system shows a vacuum instability. In a monolayer MoS2 resonator, the diamagnetic term can still play an important role in determining magnetopolariton dispersion, which is different from a monolayer graphene system. The diamagnetic term arises from electron-hole asymmetry, which indicates that electron-hole asymmetry can influence the quantum phase transition. Our study provides new insights in cavity-controlled magnetotransport in the MoS2 system, which could lead to the development of polariton-based devices.
Fri, 01 Jan 2016 00:00:00 GMThttp://hdl.handle.net/10220/468852016-01-01T00:00:00Z