Data compression on multifont Chinese character patterns

The problems arising in the modeling and coding of digital Chinese character patterns for noiseless compression purposes are discussed. The modeling is intended to capture the maximum redundancies of the source under the consideration of relevant parameters. In this study, a redundancy-gathering algorithm is proposed in which a 2-D parsing tree is used, and the nodes to extend the tree are ranked according to the maximum redundancy gathered. Hence, the modeling represented by the tree can achieve great performance in the small number of nodes. The algorithm is then applied to evaluate the performance of arithmetic coding for digital Chinese character patterns. The results are compared to those of the traditional compression methods. In the same complexity, the authors find that their algorithm can improve the coding efficiency as high as 25.54%, 30.23%, 32.17%, 15.90%, and 27.58%, for five Chinese fonts, respectively.     

Author co-citation analysis of semiconductor literature

The purpose of this study is to map semiconductor literature by author co-citation analysis in order to highlight major subject specializations in semiconductors and identify authors and their relationships within these specialties and within the field. Forty-six of the most productive authors were included in the sample list. Author samples were gathered from the INSPEC database from 1978 to 1997. The relatively low author co-citation frequencies indicate that there is a low connection among authors who publish in semiconductor journals and big differences among authors' research areas. Six sets of authors with co-citation greater than 100 times are M. Cardona and G. Lucovsky; T. Ito and K. Kobayashi; M. Cardona and G. Abstreiter; A. Y. Cho and H. Morkoc; C. R. Abernathy and W. S. Hobson; H. Morkoc and I. Akasaki. The Pearson correlation coefficient of author co-citation varies widely, i.e., from -0.17 to 0.92. This shows that some authors with high positive correlations are related in certain ways and co-cited, while other authors with high negative correlations may be rarely or never related and co-cited. Cluster analysis and multi-dimensional scaling are employed to create two-dimensional maps of author relationships in the cross-citation networks. It is found that the authors fall fairly clearly into three clusters. The first cluster covers authors in physics and its applications. The authors in the second group are experts in electrical and electronic engineering. The third group includes specialists in materials science. Because of its interdisciplinary nature and diverse subjects, semiconductor literature lacks a strong group of core authors. The field consists of several specialties around a weak center. This revised version was published online in June 2006 with corrections to the Cover Date.     

Robust control for linear uncertain systems via linear quadratic state feedback

By the Lyapunov stability criterion and the algebraic Riccati equation, conditions of selecting the weighting matrices in the quadratic cost function are derived so that linear quadratic state feedback can exponentially stabilize a linear uncertain system, provided the uncertainties satisfy the so-called matching conditions and within a given bounding set. Furthermore, two simple but effective algorithms are proposed for systematically selecting the weighting matrices. The main features of this approach are that the uncertain system can be exponentially stabilized with prescribed exponential rate and no precompensator is needed. Two examples are given to illustrate the results.     

Finding stabilized coercivity in a study of thickness and temperature dependent Co/Ag/Ge(001) ultrathin films

Epitaxial magneto-optical Co/Ag/Ge(001) ultrathin films were investigated at both room temperature and low temperature. Interesting variations in coercivity as a function of thickness and temperature suggest the existance of interfacial exchange interactions. The operative Ag layers required to inhibit intermixing of Co-Ge alloys from the oscillation of coercivity with Ag film thickness were determined. When the Ag film thickness was reduced to the submonolayer range, perpendicular anisotropy was unexpectedly found. Thus unusual phenomenon can be qualitatively discussed in terms of effective magnetic anisotropy by the contribution of reduced Co layers and by surface magnetic anisotropy.     

Comments on `Discrete optimal control with eigenvalue assignedinside a circular region'

The commenters claim that the perturbation bound for the stability of a linear optimal system derived in the paper by T.T. Lee et al. (see ibid., vol.AC-31, p.958-62 (1986)) is incorrect. The source of the error is identified and a corrected result is given. Furthermore, it is pointed out that an even more fundamental problem exists before the derivation process is started. A remedy is suggested     

A NEW MODEL FOR CAPILLARY FILTRATION BASED ON RECENT ELECTRON MICROSCOPIC STUDIES OF ENDOTHELIAL JUNCTIONS

Existing models to predict the filtration and permeability of hydrophilic solutes in the capillary interendothelial cleft have been based largely on one-dimensional models of channels with constrictions that are represented by long rectangular slits of 6 to 8 nm gap width that run along the length of the junction and do not interact with one another [1,7-10]. It has been commonly assumed based on these simple models that the water and solute fluxes are proportional to the area of the junction that is open. Recent electron microscopic studies [7, 11] using freeze fracture and ultrathin serial sectioning techniques indicate that the pores in the tight junctions might be numerous much narrower disruptions in the protein strands of 10 to 20 nm length. A new model is proposed in which the pores are short periodically distributed equivalent cylindrical holes in the junctional strands that have dimensions comparable to individual missing proteins. Since these pores have spacings which are small compared to the depth of the cleft the interaction between pores, neglected in previous models, becomes a crucial determinant of the transport behavior. A two-dimensional Hele-Shaw theory for filtration is developed to describe this interaction. This new model shows that the flux is not proportional to the length of open junction, and far fewer pores are required to accommodate the experimentally measured filtration fluxes than heretofore realized; e.g. the model predicts that only one junctional protein in eight needs to be absent to account for the measured hydraulic conductivity of frog mesentery capillaries and one in eighty for frog muscle. In contrast, traditional one-dimensional models with slit constrictions predict that the junction is open along nearly its entire length for frog mesentery capillaries and ten percent open for muscle capillaries. This basic Hele-Shaw model is then modified to describe the resistance of bridging molecules or fibers that might span the wide portions of the cleft as proposed in the fiber matrix model of Curry and Michel [16]. The results of this model depart significantly from those of the fiber matrix theory developed in [16] using the Carman-Kozeny equation and suggest that the fiber matrix, if it exists in the wide portion of the cleft, must be much more diffuse than previously predicted. The periodic fiber model shows that the Carman-Kozeny equation grossly underpredicts the filtration resistance since it neglects the influence of the channel walls on the viscous layers surrounding the fibers.     

Properties of UV-curable polyurethane acrylates: Effect of reactive diluent

Several families of UV-cured polyurethane acrylates were synthesized, and the effects of reactive diluent type and content on their physical properties were investigated. Increasing reactive diluent content promoted the development of a second, high glass transition temperature phase in all the materials, thereby leading to increased strength and modulus. Changes in the extensibility of the samples upon addition of reactive diluent were inversely related to the effect of the diluent on the crosslink density. The effects of using different reactive diluents (di-, tri-, and tetraethylene glycol diacrylate and N-vinyl pyrrolidone) on the physical properties of the samples were attributed to differences in the softening point (T_g) of the homopolymer reactive diluents and the relative compatibility of the reactive diluents with the urethane acrylate segments.     

Properties of polyurethane oligomeric blends versus high molecular weight block copolymers

Segmental compatibility has been investigated in both oligomeric polyurethane blends and polyurethane block copolymers. The block copolymers are formed by linking a hard segment, composed of three MDI and two butane diol units on average with various macroglycols. The monodisperse oligomeric hard segment, H₃, with its chain ends reacted with ethanol is used as the urethane component in blends with macroglycols. The macroglycols used in both the blend and block copolymer systems include polyethylene oxide (PEO), polypropylene oxide (PPO), polytetramethylene oxide (PTMO), and polybutadiene (PBD). Blends of H₃ and PEO form a eutectic at a weight ratio of $\text{≈20}\text{80}\text{(}\text{H}{}_3\text{/}\text{PEO}\text{)}$ with a T_m,e = 34°C. H₃ and PTMO blends also give rise to a eutectic composition at $\text{≈20}\text{80}\text{(}\text{H}{}_3\text{/}\text{PTMO}\text{)}$ but with a T_m,e = 10°C. Both PPO and PBD mix with H₃ to form a crystalline—amorphous blend. The miscibility of H₃ and the soft segments at the melting point of H₃ is in the order of PEO > PTMO > PPO > PBD. In the block copolymer systems, stress—strain and dynamic mechanical testing indicate that the block copolymerization of a hard segment with each soft segment results in a microphase separated elastomer as expected. The extent of phase separation increases in the order of PBD > PTMO > PPO > PEO which is coincident with the trend predicated by the application of Hilderbrand's solubility parameter concept. All the soft segments used occur in an amorphous phase in the block copolymers while PEO and PTMO crystallize in a blend with H₃. The differences between the properties of the blends and block copolymers suggest that the phase separation, segment crystallization and domain coalescence are substantially restricted by the urethane—polyol junction points.     

Natural convective characteristics of a heat source module at different angles in the closed and ventilated cabinets

A numerical analysis is performed to study the characteristics of heat transfer from a block heat source module at different angles in two-dimensional cabinets. Great efforts are carried out to conduct the effects of thermal interaction between the air steams inside and outside the cabinet on the conjugate conduction–natural convection phenomena. Moreover, the enhancement of cooling performance of the heat source module through the construction of air vents on cabinet wall is rigorously examined. The computation domain covers the cabinet and the surrounding area, and the temperature and velocity fields of the cabinet and surrounding area are solved simultaneously. Comparing the results for cases with and without the consideration of thermal interaction between the air streams, the difference in hot spot temperature of module can be up to 26% for Pr = 0.7, K_bf = K_wf = 100, 0 ≦ K_pf ≦ 100, 10⁵ ≦ Ra ≦ 10⁷ and φ = 0°, 90°, 270°. The maximum reduction in hot spot temperature is about 41% when two air vents are constructed on the cabinet wall. The variation of module angle results in the maximum difference of the hot spot temperature is 17% for closed cabinet, and 10% for ventilated cabinet. In addition, the hot spot temperatures for cases with K_pf = 10 are about two times of that for K_pf = 100.     

Radiative transfer simulation of dust-like aerosols: Uncertainties from particle shape and refractive index

The composition, particle shape, number concentration, size distribution, and spatial and temporal distributions of dust aerosols cause significant uncertainties in relevant radiative transfer simulations. The spherical particle approximation has been generally recognized to introduce errors in radiative transfer calculations involving dust aerosols. Although previous studies have attempted to quantify the effect of non-spherical particles, no consensus has been reached as to the significance of the dust aerosols non-spherical effect on flux calculations. For this study, we utilize a newly developed ultra-violet-to-far-infrared spectral database of the single-scattering properties of tri-axial ellipsoidal, mineral dust-like aerosols to study the non-spherical effect on radiative forcing. The radiance and flux differences between the spherical and ellipsoidal models are obtained for various refractive indices and particle size distributions. The errors originating from using the spherical model and the uncertainties in the refractive indices are quantified at both the top and bottom of the atmosphere. The dust non-spherical effect on the net flux and heating rate profile is obtained over the entire range of the solar spectrum. The particle shape effect is found to be related to the dust optical depth and the surface albedo and can be an important uncertainty source in radiative transfer simulation. The particle shape effect is largest over water surfaces and can cause up to a 30% difference in dust forcing at the top of the atmosphere.