Scheduling for electricity cost in a smart grid

We study an offline scheduling problem arising in demand response management in a smart grid. Consumers send in power requests with a flexible set of timeslots during which their requests can be served. For example, a consumer may request the dishwasher to operate for 1 h during the periods 8am to 11am or 2pm to 4pm. The grid controller, upon receiving power requests, schedules each request within the specified duration. The electricity cost is measured by a convex function of the load in each timeslot. The objective of the problem is to schedule all requests with the minimum total electricity cost. As a first attempt, we consider a special case in which the power requirement and the duration a for which a request needs service are both unit-size. For this problem, we present a polynomial time offline algorithm that gives an optimal solution and shows that the time complexity can be further improved if the given set of timeslots forms a contiguous interval.     

On-line Stream Merging with Max Span and Min Coverage

This paper introduces the notions of span and coverage for analyzing the performance of on-line algorithms for stream merging. It is shown that these two notions can solely determine the competitive ratio of any such algorithm. Furthermore, we devise a simple greedy algorithm that attains the ideal span and coverage, thus giving a better performance guarantee than existing algorithms. The new notions also allow us to obtain a tighter analysis of existing algorithms.     

Improved on-line broadcast scheduling with deadlines

We study an on-line broadcast scheduling problem in which requests have deadlines, and the objective is to maximize the weighted throughput, i.e., the weighted total length of the satisfied requests. For the case where all requested pages have the same length, we present an online deterministic algorithm named BAR and prove that it is 4.56-competitive. This improves the previous algorithm of (Kim, J.-H., Chwa, K.-Y. in Theor. Comput. Sci. 325(3):479–488, 2004) which is shown to be 5-competitive by (Chan, W.-T., et al. in Lecture Notes in Computer Science, vol. 3106, pp. 210–218, 2004). In the case that pages may have different lengths, we give a ( )-competitive algorithm where Δ is the ratio of maximum to minimum page lengths. This improves the (4Δ+3)-competitive algorithm of (Chan, W.-T., et al. in Lecture Notes in Computer Science, vol. 3106, pp. 210–218, 2004). We also prove an almost matching lower bound of Ω(Δ/log Δ). Furthermore, for small values of Δ we give better lower bounds. The work described in this paper was fully supported by grants from the Research Grants Council of the Hong Kong SAR, China [CityU 1198/03E, HKU 7142/03E, HKU 5172/03E], an NSF Grant of China [No. 10371094], and a Nuffield Foundation Grant of UK [NAL/01004/G].     

Antimicrobial and biodegradable materials based on ε-caprolactone derivatives

Appropriate wound care is pivotal in preventing wound and postsurgery infections, which remain a serious clinical problem. In this study, we report the successful fabrication of antimicrobial and biodegradable materials for possible use in the medical field. Amino functionalized polycaprolactone (PCL [Poly(CL-co-ACL)]) was synthesized via ring opening polymerization. This polymer was then functionalized via the pendant amine to induce antimicrobial efficacy. This was done through the grafting of poly(lysine) onto the amine as well as the quaternization of the amine using alkyl halides. The chemical structures of the synthesized monomers and polymers were confirmed using nuclear magnetic resonance (¹H NMR and ¹³C NMR) spectroscopy and attenuated total reflection-Fourier transform infrared spectroscopy. The molecular weights of the polymers were determined using gel permeation chromatography. Nanofibre scaffolds were produced from the polymers using the electrospinning technique and these were characterized though scanning electron microscopy. The antimicrobial efficacy of the fabricated materials was tested against the Gram-positive (Staphylococcus aureus ATCC 25923) and Gram-negative (Pseudomonas aeruginosa ATCC 27853) bacteria using the disc diffusion and shake flask methods. The polymers demonstrated excellent antimicrobial efficacy. The fibers were exceptionally biodegradable which opens a lot of applications in the biomedical space.     

Edge photoluminescence of single-crystal silicon at room temperature

The edge photoluminescence of single-crystal silicon (c-Si) with a peak at ～1.09 eV at room temperature is observed for structures that consist of nanocrystalline silicon (nc-Si) and c-Si. The structures are obtained by pulsed-laser deposition of an nc-Si film onto a c-Si substrate. The photoluminescence signal increases as both the density of surface states at the nc-Si/c-Si boundary and the scattering of the edge emission from c-Si in the nc-Si film decreases.