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Almost tight upper bound for finding Fourier coefficients of bounded pseudo-Boolean functions
Choi, S.S.,Jung, K.,Kim, J.H. Academic Press 2011 Journal of Computer and System Sciences Vol.77 No.6
A k-bounded pseudo-Boolean function is a real-valued function on {0,1}<SUP>n</SUP> that can be expressed as a sum of functions depending on at most k input bits. The k-bounded functions play an important role in a number of areas including molecular biology, biophysics, and evolutionary computation. We consider the problem of finding the Fourier coefficients of k-bounded functions, or equivalently, finding the coefficients of multilinear polynomials on {-1,1}<SUP>n</SUP> of degree k or less. Given a k-bounded function f with m non-zero Fourier coefficients for constant k, we present a randomized algorithm to find the Fourier coefficients of f with high probability in O(mlogn) function evaluations. The best known upper bound was O(λ(n,m)mlogn), where λ(n,m) is between n<SUP>12</SUP> and n depending on m. Our bound improves the previous bound by a factor of Ω(n<SUP>12</SUP>). It is almost tight with respect to the lower bound Ω(mlognlogm). In the process, we also consider the problem of finding k-bounded hypergraphs with a certain type of queries under an oracle with one-sided error. The problem is of self interest and we give an optimal algorithm for the problem.
Choi, I.T.,You, B.S.,Eom, Y.K.,Ju, M.J.,Choi, W.S.,Kang, S.H.,Kang, M.S.,Seo, K.D.,Hong, J.Y.,Song, S.H.,Yang, J.W.,Kim, H.K. Elsevier Science 2014 ORGANIC ELECTRONICS Vol.15 No.11
Triarylamine-based dual-function coadsorbents containing a carboxylic acid acceptor linked by extended π-conjugation aryl linkers (e.g., phenylene: HC-A3, naphthalene: HC-A4 and anthracene: HC-A5) were newly designed and synthesized. They were used as coadsorbents in organic dye-sensitized solar cells (DSSCs) based on a porphyrin dye (hexyloxy-biphenyl-ZnP-CN-COOH (HOP)). For comparison, the π-conjugated phenyl linker (HC-A3) previously developed by our group was also used as a coadsorbent. The structural effects on the photophysical and electrochemical properties and DSSC performance were systematically investigated. As a result, the DSSCs based on HC-A4 and HC-5 displayed power conversion efficiencies (PCEs) of 8.2% and 5.1%, respectively, while the HC-A3-based DSSC achieved a PCE of 7.7%. In the case of HC-A4, both the short-circuit photocurrent densities (J<SUB>sc</SUB>) and open-circuit voltages (V<SUB>oc</SUB>) of DSSCs were simultaneously improved to a large extent due to the more effective prevention of π-π stacking of organic dye molecules and the better light-harvesting effect at short wavelengths. The HC-A5-based DSSC exhibited a much lower short-circuit current (J<SUB>sc</SUB>) and open-circuit voltages (V<SUB>oc</SUB>) compared to the HC-A4-based DSSC, due to the fact that the dihedral angle of the π-conjugated linkers was too high for electron injection into the TiO<SUB>2</SUB> conduction band (CB) level. This had a reduced effect on preventing the π-π stacking of dye molecules, resulting in lower J<SUB>sc</SUB> and V<SUB>oc</SUB> values.
Novel K/Ka Bandpass Filters using LIGA Micromachined Process
Park, K. Y.,Park, J. Y.,Choi, H. K.,Lee, J.C.,Lee, B.,Kim, J. H.,Kim, N. Y.,Park, J. Y.,Kim, G. H.,Kim, D. W.,Bu, J. U.,Chung, K. W. The Korean Institute of Electromagnetic Engineerin 2000 한국전자파학회논문지 Vol.11 No.6
New class of three dimensional (3-D) micromachined microwave planar filters at K and Ka-band are presented using LIGA micro-machined process. The K-and Ka-band filters show wide bandpass characteristics of~36% and ~39% with the insertion loss 1.26dB at 19.11GHz and 1.7dB at GHz, respectively. These filters can be applicable in high power MMIC of MIMIC.
Baek, J.Y.,Choi, C.M.,Eun, H.J.,Park, K.S.,Choi, M.C.,Heo, J.,Kim, N.J. North Holland 2015 Chemical physics letters Vol.635 No.-
We obtain the ultraviolet photodissociation spectrum of adenine complexes with K<SUP>+</SUP> ion stored in a cold ion trap. The spectrum near the origin band of the S<SUB>0</SUB>-S<SUB>1</SUB> transition exhibits well-resolved vibronic bands, all of which are assigned from a single isomer by UV-UV hole-burning (HB) spectroscopy. Comparing the spectrum with theoretical spectra, we determine the structure of the isomer, where K<SUP>+</SUP> is bound not to 9H-adenine (A9) but to 7H-adenine (A7). We suggest that K<SUP>+</SUP>A7 ions are formed in solution through tautomerization, for which the energy barrier varies greatly depending on the binding site of the K<SUP>+</SUP> ion on A9.