bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Flow Baffles on the Dialysate Flow Distribution of Hollow-Fiber Hemodialyzers: A Nonintrusive Experimental Study Using MRI
Authors: Poh Churn K. , Hardy Peter A. , Liao Zhijie , Huang Zhongping , Clark William R. , Gao Dayong
Published: August 2003

We used an innovative, nonintrusive MRI technique called the two-dimensional (2D) Phase-Contrast (2DPC) velocity-imaging technique to investigate the effect of flow baffles on the dialysate-side flow distribution in two different hollow-fiber hemodialyzers (A and B); each with flow rates between 200 and 1000 mL/min (3.33×10−6 and 1.67×10−5 m3/s). Our experimental results show that (1) the dialysate-side flow distribution was nonuniform with channeling flow occurred at the peripheral cross section of these hollow-fiber hemodialyzers, and (2) the existing designs of flow baffles failed to promote uniform dialysate-side flow distribution for all flow rates studies.
Measured Impact of a Rooftop Photovoltaic System
Authors: Fanney A. Hunter , Weise Eric R. , Henderson Kenneth R.
Published: August 2003

A 35-kW rooftop photovoltaic (PV) system has been installed at the National Institute of Standards and Technology (NIST) in Gaithersburg, Maryland. The system, located on the flat roof that connects NIST’s Administration Building to its adjoining conference and cafeteria facilities, produced NIST’s first site-generated renewable energy on September 14, 2001. In addition to providing electrical energy and reducing monthly peak electrical loads, the rear surface of each module is laminated to 51 mm of extruded polystyrene enhancing the thermal performance of the roof. A unique ballast system secures the photovoltaic system, eliminating the need for roof penetrations. An instrumentation and data acquisition package was installed to record the ambient temperature, wind speed, solar radiation, and the electrical energy delivered to the grid. Additional solar radiation instruments were installed after determining that the original solar radiation sensor was influenced by reflections from the south-facing wall of the Administration Building’s tower. NIST’s electric utility billing schedule includes energy and peak demand charges. The generation charges vary significantly depending upon the time interval—off-peak, intermediate, and on-peak—during which the energy is consumed. The schedule is divided into summer billing months (June–October) and winter billing months (November–May). During the winter billing months, the distribution, transmission, and generation peak demand charges are based on the greatest power demand imposed by the site on the grid. During the summer billing months, an additional demand charge is imposed to capture electrical demand during the on-peak time interval. This paper summarizes the monthly and annual measured performance of the photovoltaic system. The monthly energy produced by the system is tabulated. The system has provided 35676 kWh of electrical energy during its first year of operation. Conversion efficiencies—computed using solar radiation measurements from a single photovoltaic cell radiation sensor, four thermopile-based radiation sensors located around the perimeter of the photovoltaic array, and a remotely located thermopile-based radiation sensor—are presented. Annual conversion efficiencies of 10.8%, 8.8%, and 7.4% were achieved using cell, module, and foot print areas, respectively. Using the electric utility’s rate schedule, the monetary savings credited to the photovoltaic system is determined by combining the cost of the displaced energy with the reduction in peak demand charges attributable to the photovoltaic system. During its first year of operation, the system has saved $2678 with savings in demand charges, essentially equivalent to savings as a result of displaced energy. Finally, using utility provided data and the Environmental Protection Agency’s (EPA) Environmental Benefits Calculator, estimates are made of the avoided emissions of the photovoltaic system over its projected life span.
Genetic Algorithms for Optimization of Building Envelopes and the Design and Control of HVAC Systems
Authors: Caldas L. G. , Norford L. K.
Published: August 2003

Many design problems related to buildings involve minimizing capital and operating costs while providing acceptable service. Genetic algorithms (GAs) are an optimization method that has been applied to these problems. GAs are easily configured, an advantage that often compensates for a sacrifice in performance relative to optimization methods selected specifically for a given problem, and have been shown to give solutions where other methods cannot. This paper reviews the basics of GAs, emphasizing multi-objective optimization problems. It then presents several applications, including determining the size and placement of windows and the composition of building walls, the generation of building form, and the design and operation of HVAC systems. Future work is identified, notably interfaces between a GA and both simulation and CAD programs.
Controls and Diagnostics for Air Distribution Systems
Authors: House John M. , Lee Kwangduk Douglas , Norford Leslie K.
Published: August 2003

Fault detection and diagnostics applied to heating, ventilating, and air-conditioning (HVAC) equipment has been an active area of research over the past decade, with much of the work focusing on air distribution systems. Concurrent efforts have sought to improve the control of these systems. This paper discusses the relationship between controls and diagnostics for air distribution systems, provides an overview of the diagnostic literature for these systems, presents new findings from a diagnostic method that enables operational characteristics of individual HVAC components to be extracted from high-frequency measurements of whole-building power, and outlines research challenges that remain to be addressed.
Airborne Infection Control in Health Care Facilities
Authors: Kuehn Thomas H.
Published: August 2003

Documented correlations between building occupant health effects and exposure to indoor airborne contaminants are very limited because of low indoor concentrations and confounding exposure elsewhere. However, an important exception has been found in hospitals where immune compromised patient mortality has been directly linked to increased indoor airborne fungal contamination caused by construction activity. Inhalation of viable Aspergillus spores often results in invasive pulmonary aspergillosis, a disease with a high fatality rate. A review of the literature is given and recommendations and needs are outlined for barriers, filtration, air pressure control and bioaerosol sensors.
Advances in Solar Buildings
Authors: Walker Andy , Renne´ David , Bilo Susan , Kutscher Chuck , Burch Jay , Balcomb Doug , Judkoff Ron , Warner Cecile , King Richard J. , Eiffert Patrina
Published: August 2003

In the autumn of 2002, 14 universities built solar houses on the National Mall in Washington, DC, in a student competition—the Solar Decathlon—demonstrating that homes can derive all the energy they need from the sun and celebrating advances in solar buildings. This paper describes recent progress in solar building technology that expands the designer’s palette and holds the potential to radically improve building energy performance. The discussion includes market conditions and solar resource data; design integration and modeling; window technology, daylighting, passive solar heating; solar water heating; solar ventilation air preheating; building-integrated photovoltaics; and solar cooling. The Solar Decathlon competition highlighted ways in which these strategies are integrated in successful solar buildings.
Continuous CommissioningSM of Building Energy Systems
Authors: Liu Mingsheng , Claridge David E. , Turner W. D.
Published: August 2003

Continuous Commissioning (CCSM) is an ongoing process to resolve operating problems, improve comfort, optimize energy use, and identify retrofits for existing commercial and institutional buildings and central plant facilities. CC focuses on optimizing/improving overall system control and operations for the building as it is currently utilized and on meeting existing facility needs. Innovative optimal engineering solutions are developed using engineering-based model analysis integrated with scientific field measurement. Integrated approaches are used to implement these solutions to ensure practical local and global system optimization and to ensure persistence of the improved operational schedules. Implementation of the CC process has typically decreased building energy consumption by 20% in well over 100 large buildings where it has been implemented. This paper presents the CC process, the primary CC techniques and measures, and a case study.
Decontamination of Ventilation Systems Using Photocatalytic Air Cleaning Technology
Authors: Goswami D. Yogi
Published: August 2003

Indoor air pollution is caused by particulate matter and chemical and microbial contamination. Conventional technologies, including filteration, do not adequately provide complete answers to these problems. Photocatalytic oxidation combined with filteration provides one of the most viable solutions to the problem of indoor air contamination by microorganisms and volatile organic chemicals (VOCs). It can also provide a defense against bioterrorism. This paper describes the theoretical background of the technology and results of its effectiveness against VOCs, bacteria, spores, and dust mite allergens. Although the technology uses UV photons from blacklight, it can be designed to use sunlight with the help of fiber optics.
A Numerical Study of Swage Autofrettage
Authors: Iremonger Michael J. , Kalsi Gurdip S.
Published: August 2003

This paper describes a numerical analysis of the swaging autofrettage of a gun barrel by forcing an oversize mandrel (or “swage”) through the barrel. Analyses are conducted on a two pass swaging procedure in which two separate swages are driven through the barrel. Differences between the maximum swage force required and the resulting barrel deformations and stresses that result from single and two pass swaging are discussed. The effects of changes to swage geometry for single pass swaging are also considered.
On Thick-Walled Cylinder Under Internal Pressure
Authors: Zhao W. , Seshadri R. , Dubey R. N.
Published: August 2003

A technique for elastic-plastic analysis of a thick-walled elastic-plastic cylinder under internal pressure is proposed. It involves two parametric functions and piecewise linearization of the stress-strain curve. A deformation type of relationship is combined with Hooke’s law in such a way that stress-strain law has the same form in all linear segments, but each segment involves different material parameters. Elastic values are used to describe elastic part of deformation during loading and also during unloading. The technique involves the use of deformed geometry to satisfy the boundary and other relevant conditions. The value of strain energy required for deformation is found to depend on whether initial or final geometry is used to satisfy the boundary conditions. In the case of low work-hardening solid, the difference is significant and cannot be ignored. As well, it is shown that the new formulation is appropriate for elastic-plastic fracture calculations.
Emission uniformity improvement of Si field emitter arrays by surface modification
Authors: Nagao M. , Nicolaescu D. , Matsukawa T. , Kanemaru S. , Itoh J. , Koga K. , Kawase T. , Honda K. , Norikane T.
Published: August 2003

The emission uniformity of Si field emitter arrays (FEAs) with 1024 tips were evaluated by using electrostatic lens projector. Some surface modifications were applied to the Si FEA for improving the emission uniformity. A combination of CHF3 plasma and preheat treatments is very effective for cleaning the tip surface and for improving the uniformity of the work function distribution in the array. The number of working tips increased by a factor of 5 after the preheat treatment at the temperature of 450 °C. For further improvement, high current pulses were applied to the FEA. The pulse drive is effective for improving the uniformity of the tip radius. By applying all of the treatment and driving methods, more than half of the array emitters could be activated even for small operating current of 5 μA.
Broad area electron emission from oxygen absorbed homoepitaxially grown nitrogen (N)-doped chemical vapor deposited diamond (111) surface
Authors: Yamaguchi Hisato , Mine Takuya , Suzuki Yu , Okano Ken , Yamada Takatoshi , Sawabe Atsuhito
Published: August 2003

One of the clear visions of microelectronic device engineering has been to replace the thermal cathode by a “cold” emitting cathode. The main advantages of using a cold cathode are that it is smaller and consumes less energy than its thermal counterpart. For a long time the main obstacle to designing such a device was the inability of achieving a broad area low-threshold electron emission from material of interest. This study reports surprisingly broad area low-threshold emission from homoepitaxially grown N-doped chemical vapor deposited (CVD) diamond (111), which was never achieved with polycrystalline diamond. Moreover, there was a strong correlation between the oxygen absorbed site and emission site. Our results suggest a superhard, metastable planar cold cathode with a desired emission site can be obtained by homoepitaxially grown N-doped CVD diamond (111) with selective oxygen absorption.
Deterioration of ZnS-type and Eu3+-activated phosphors for high-voltage field-emission displays
Authors: Kajiwara K.
Published: August 2003

Deterioration of luminescence efficiency η of blue- and green-emitting ZnS-type phosphors, and red-emitting Eu3+-activated phosphors has been studied for high-voltage field emission displays (FEDs). In the blue-emitting ZnS:Ag,Al(Cl) phosphor (P22B and P55) case, the deterioration of η depends mainly on the crystallinity of the host crystal within the electron penetration depth d. It was found that a high-voltage FED tube having a longer lifetime was successfully prepared by using a crystalline-improved ZnS:Ag,Al phosphor. While, in the green-phosphor case, in order to optimize the donor–acceptor (D–A) pair density in ZnS:Cu,Al (P22G) for a suitable color gamut in FEDs, various ZnS:Cu,Al phosphors with low defect density were prepared by using a suitable firing method with a surface treatment like an improved ZnS:Ag,Al phosphor. It was found that the deterioration of improved ZnS:Cu,Al phosphors depends mainly on the D–A pair density in ZnS crystal. Furthermore, in the red-phosphor case, deterioration of Y2O2S:Eu3+ phosphor (P22R) for color-TV has been studied in comparison with a Y2O3:Eu3+(P56) for projection CRTs. It was found that a Y2O2S:Eu3+ phosphor shows a longer luminescence lifetime than a Y2O3:Eu3+ phosphor in high-voltage FEDs. These evidences suggest that the factors influencing the deterioration of luminescence efficiency in ZnS-type and Eu3+-activated phosphors for high-voltage FEDs are the crystallinity of the host crystal, the density of luminescence centers (i.e., susceptibility to the electron irradiation-induced lattice-defects), and the host material (i.e., susceptibility to surface chemical stability).
High-resolution scanning tunneling microscopy imaging of Escherichia coli lysine transfer ribonucleic acid
Authors: Nishimura Makoto , Tanaka Hiroyuki , Kawai Tomoji
Published: August 2003

We have obtained high-resolution scanning tunneling microscopy (STM) images of Escherichia coli lysine transfer ribonucleic acid (tRNA) adsorbed onto Cu(111) substrates using a pulse injection method. One of the two arms of the L-shaped structure of the observed tRNA is longer than the other. Because hydrogen bonds that maintain the unique three-dimensional structure of tRNAs exist in the hinge region and in one arm of L-shaped structures that include the anticodon stem, we concluded that the longer arm in the L-shaped structure includes the anticodon stem, and the shorter arm includes the acceptor stem. This work supports the view that STM is a powerful tool for obtaining high-resolution images of biomolecules that are too difficult to crystallize.
Etch mechanism and etch-induced effects in the inductively coupled plasma etching of GaN
Authors: Cheung R. , Rong B. , van der Drift E. , Sloof W. G.
Published: August 2003

The inductively coupled plasma (ICP) processing of gallium nitride (GaN) using SF6/N2 and Cl2/Ar gas mixtures has been compared. ICP processing of GaN using SF6 and N2 mixture of 1:1 produces an optimized etch rate of 67 nm/min while five times higher etch rate of 314 nm/min is achieved using Cl2 and Ar mixture of 1:3. Etch mechanism studies indicate an ion-induced, coupled with a large chemical enhancement component for both SF6/N2 and Cl2/Ar inductively coupled plasma etching. From electrical diode characterization, an increase in electrical degradation with increasing dc bias in Cl2/Ar plasma is observed, while an improvement of diode characteristics is evident after etching in SF6/N2 plasma. X-ray photoelectron spectroscopy results indicate the presence of a significantly Ga deficient surface after etching GaN in Cl2 and Cl2/Ar plasmas. Correlation between etch mechanism and etch-induced damage results strongly indicates the existence of ion-induced chemical damage in the ICP etching of GaN in Cl2 and Cl2/Ar plasmas.
Gas-induced current decay of molybdenum field emitter arrays
Authors: Reuss Robert H. , Chalamala Babu R.
Published: August 2003

Field emission displays can be seriously limited by current degradation of Mo field emitter arrays, primarily due to inadequate vacuum conditions inside their thin vacuum packages. Most lifetime studies describe the deleterious effects of short exposures to oxygenic gases on device performance. Here, we review experimental results on the emission characteristics of molybdenum field emitter arrays in a variety of gas ambients for extended periods. We find that even in inert gas, the emission current degrades rapidly, comparable to that observed in oxygenic gas ambients. Surprisingly, after exposure when the device is again operated under high vacuum conditions, various levels of current recovery can be observed. No evidence for ion sputter damage is observed. Existing degradation models do not provide an adequate explanation for this behavior. Rather, we suggest that these results point toward a model common for all gaseous ambients based on shallow implantation of ions into the field emitter tips. This creates a near surface layer that modifies the tunneling barrier, and thus subsequently the emission current. Support for this mechanism comes from several experimental observations. The implant degradation model is also consistent with devices that incorporate a field emitter ion pump process as a means to reduce pressure in the sealed vacuum package.
Simulation of triode-type field emitters with thin-film cathodes
Authors: Park Kyung Ho , Lee Soonil , Koh Ken Ha
Published: August 2003

We carried out two-dimensional numerical calculations of electrostatic potential for triode field emitters with planar cathodes using the finite-element method. As it turned out, the conventional triode structure with a planar cathode suffered from large gate current and wide spreading of emitted electrons. To circumvent these shortcomings, we proposed another triode structure. By simply inserting a conducting layer of proper thickness between the gate insulator and the cathode layer, we were able to modify the electric-field distribution on the cathode surface so that low gate current and electron-focusing effect were achieved, simultaneously.
Ferromagnetism in Mn- and Co-implanted ZnO nanorods
Authors: Ip K. , Frazier R. M. , Heo Y. W. , Norton D. P. , Abernathy C. R. , Pearton S. J. , Kelly J. , Rairigh R. , Hebard A. F. , Zavada J. M. , Wilson R. G.
Published: August 2003

ZnO nanorods with diameters of 15–30 nm were grown on Ag-coated Si substrates by catalyst-driven molecular beam epitaxy and then implanted with Mn+ or Co+ ions to doses of 1–5×1016 cm−2. After subsequent annealing at 700 °C for 5 min, the structural properties of the nanorods were unaffected, but they exhibited ferromagnetism that persisted to temperatures of 225–300 K. The coercive fields were ⩽100 Oe even at 10 K. The results are similar to those obtained for implantation of Mn+ or Co+ ions in bulk single-crystal ZnO and indicate promise for nanorods for nanoscale spintronic applications.
Modeling of vacancy flux due to stress-induced migration
Authors: Aoyagi Minoru
Published: August 2003

The stress-induced migration phenomenon is one of the problems related to the reliability of metal interconnections on semiconductor devices. The phenomenon causes voids and fractures to occur in the interconnections when the semiconductor devices are maintained at a high temperature for long periods. The purpose of this study is to theoretically clarify the temperature characteristics of the phenomenon. First, the residual thermal stress and the vacancy concentration in the interconnection with a slitlike void were calculated based on fundamental discussions on the residual thermal stress and the vacancy concentration in the interconnection without voids. Next, the vacancy flux to the slitlike void was considered at various temperatures. The theoretical results reveal that the temperature characteristic of the vacancy flux has a peak at a certain temperature which changes due to stress relaxation. Therefore, the temperature facilitating easy void formation shifts to a lower value with void expansion. Finally, the results of the theoretical analyses were compared with the results of high-temperature storage tests of samples. The theoretical results qualitatively agree with the results of the tests.
Mechanisms of lateral ordering of InAs/GaAs quantum dot superlattices
Authors: Chen W. , Shin B. , Goldman R. S. , Stiff A. , Bhattacharya P. K.
Published: August 2003

We have investigated the mechanisms of lateral ordering of InAs/GaAs quantum dot superlattices. Using cross-sectional scanning tunneling microscopy, we determined the lateral spacing between dot columns in a series of five-period dot superlattices annealed for various times. As the annealing time is increased, the average column spacing increases, while the distribution of column spacings is broadened. A comparison with earlier studies of one-, five-, ten-, and twenty-period dot superlattices suggests that the lateral column spacing is determined by strain-enhanced bulk diffusion. We propose a conceptual model for self-ordering of quantum dot superlattices based upon a combination of island nucleation plus strain-enhanced island dissolution.
Polarity control during molecular beam epitaxy growth of Mg-doped GaN
Authors: Green D. S. , Haus E. , Wu F. , Chen L. , Mishra U. K. , Speck J. S.
Published: August 2003

Mg doping has been found in some situations to invert growth on Ga-face GaN to N-face. In this study, we clarified the role the Ga wetting layer plays in rf plasma molecular beam epitaxy of GaN when Mg doping, for [Mg] from ∼2×1019 to ∼1×1020 cm−3 corresponding to the useful, accessible range of hole concentrations of p∼1017–1018 cm−3. Structures were grown in the N-rich and Ga-rich growth regime for single Mg doping layers and for multilayer structures with a range of Mg concentrations. Samples were characterized in situ by reflection high-energy electron diffraction and ex situ by atomic force microscopy, transmission electron microscopy, convergent beam electron diffraction, and secondary ion mass spectroscopy. Growth on “dry” surfaces (without a Ga wetting layer) in the N-rich regime completely inverted to N-face upon exposure to Mg. No reinversion to Ga-face was detected for subsequent layers. Additionally, Mg was seen to serve as a surfactant during this N-rich growth, as has been reported by others. Growth initiated in the Ga-rich regime contained inversion domains that nucleated with the initiation of Mg doping. No new inversion domains were found as the Mg concentration was increased through the useful doping levels. Thus the Ga wetting layer was found to inhibit nucleation of N-face GaN, though a complete wetting layer took time to develop. Finally, by establishing a complete Ga wetting layer on the surface prior to growth, we confirmed this finding and demonstrated Mg-doped GaN completely free from inversion domains to a doping level of [Mg]∼2×1020.
Oxygen species in Cs/O activated gallium nitride (GaN) negative electron affinity photocathodes
Authors: Machuca Francisco , Liu Zhi , Sun Yun , Pianetta P. , Spicer W. E. , Pease R. F. W.
Published: August 2003

Negative electron affinity (NEA) photocathode electron sources operating within sealed off tubes (closed vacuum) and demountable vacuum systems (open vacuum), suffer from different factors that affect the initial high performance and longevity. To aid in the understanding of the factors affecting an open vacuum system, the chemistry of a cesium and oxygen (Cs/O) adlayer was investigated, focusing on the role of oxygen during the NEA co-deposition process (activation) and operation of a GaN (0001) emitter. Synchrotron radiation photoemission spectroscopy and a focused mercury arc discharge lamp are used for analyzing surface chemical species and total quantum yield, respectively, as the photocathode ages. The results for the activation within a demountable vacuum system indicated: (1) oxygen concentration increased over time on the Cs/O activated surface independent of the starting substrate as observed in related studies of InP (100) and GaAs (100), (2) the dominant initial oxygen species is assigned to an ion of molecular oxygen (di-oxygen) in the Cs/O activation layer having −2 charge state that changes to the −1 charge state as the quantum yield decays, and (3) the chemical changes of the Cs/O adlayer are not accompanied by a significant loss of cesium from the surface, but instead an increase in oxygen from the open vacuum system occurred. We present a chemical model for the activation layers and their transformation over time consistent with observations (1) through (3). The quantum efficiency (QE) from the GaN (0001) photocathode remained constant within a few percent over a 10 h period at ⩾20% QE and decayed by less than a factor of 2 over the subsequent 7 h as the chemical changes at the surface took place. The slowly decreasing monotonic yield gives preliminary evidence that GaN is a prospect for a more robust emitter. A long lived photocathode of this type offers near constant quantum yield over several hours when operating within open vacuum conditions by simply adjusting laser power with a feedback circuit. On the other hand, this decay can most certainly be avoided in sealed tubes by maintaining a pristine closed off environment with the proper over pressure of Cs. A detailed account of the effects of the chemical changes in the Cs/O adlayer on the resulting emission properties for GaAs and GaN (open vacuum) are discussed in a separate report [F. Machuca et al., J. Vac. Sci. Technol. B 20, 2721 (2002)].
Pattern multiplication method and the uniformity of nanoscale multiple lines
Authors: Chung Kyung-Hoon , Choi Woo Young , Sung Suk-Kang , Kim Dae Hwan , Lee Jong Duk , Park Byung-Gook
Published: August 2003

We have developed a patterning technique to define ultrafine lines with high density and good uniformity using sidewall structures. Approximately 50 nm multiple lines, which have 70 nm as the narrowest space between the lines, are defined by the pattern multiplication technique. Linewidths are measured at several points on wafers and their uniformity is verified. These patterns have a good uniformity (deviation 2.26–4.35 nm). Also, die-to-die uniformity is very good. The advantage of this technique is the easy control (using sidewall width control) of the line and space of patterns. This technique is free from the proximity effect because of the process using a sidewall hard mask. Thus, it is expected that the pattern multiplication technique can be applied to fabricate single electron devices, quantum devices, and other nanoscale devices.
Three-dimensional measurement and analysis of the light emitted from Ne–Xe (4%) alternating current plasma display panel by an optical method
Authors: Choi Hoon-Young , Lee Seok-Hyun , Lee Seung-Gol
Published: August 2003

In order to understand the discharge phenomenon within a plasma display panel (PDP) cell thoroughly and in particular its three-dimensional effect, the three-dimensional measurement should be taken and studied. Thus, the scanned point detecting system, which consists of an optical microscope with a point detector and a scanning stage, is proposed for the spatial three-dimensional measurement of the light emitted from Ne–Xe (4%) PDP. The characteristics of the three-dimensional discharge phenomenon are analyzed by using the proposed system. From the intensity distributions of 600 nm wavelength light, it is shown that the light which is detected at the inside edge of an indium tin oxide electrode is stronger than any other points and the light intensity which is detected at the center between the barrier ribs is stronger than near the barrier ribs. Also, the 828 nm light shows a broad distribution which reaches the outside edge of the bus electrode. The reason is that the 828 nm light is emitted from Xe* (2p5) state which is easily excited by the weak electric field. Finally, we found that the intensity of 450 nm blue phosphor light located at the upper side of the barrier ribs is stronger than the bottom side.
Downstream oxygen etching characteristics of polymers from the parylene family
Authors: Callahan Russell R. A. , Pruden Kristin G. , Raupp Gregory B. , Beaudoin Stephen P.
Published: August 2003

As dictated by the International Technology Roadmap for Semiconductors, there is an immediate need to develop low dielectric materials for use in metalization and packaging schemes in integrated circuits. The etching characteristics of a family of low dielectric polymers, the parylenes, are discussed. These are good models for polymer dielectrics, and are attractive for packaging applications. Three types of parylene are studied: parylene-N, parylene-C, and parylene AF-4. Parylene films on silicon substrates were etched in a downstream microwave oxygen plasma system. The goal was to characterize the chemical reactions that occurred on the parylene in the afterglow of the microwave oxygen plasma. The effect of temperature on the etch rate of each polymer was studied and an apparent activation energy was determined. The apparent activation energy for the etch process is approximately 7.0 kcal/mol for each polymer. Infrared analysis showed carbonyl formation during etching in the parylene-N and -C. Based on these analyses and the calculated activation energies, it was determined that a likely rate-limiting step in the etching was the ring opening.
Computer simulation of the field emission properties of multiwalled carbon nanotubes for flat panel displays
Authors: Hu Yuan , Huang C.-H.
Published: August 2003

Multiwalled carbon nanotubes (MWCNTs) have great potential in several applications such as being field emitters for flat panel displays. A particle-in-cell computer simulation code MAGIC was used in this work to investigate the field emission characteristics of both closed-capped and open-ended MWCNTs. The influence of various geometric parameters on the field emission properties of MWCNTs, such as the radius of curvature of the tips for the closed tubes, the edge sharpness, the inner and outer diameters of the open tubes, and the distance between neighboring tubes, are particularly studied. It is found that the circular corner edges of the open-ended MWCNT has to be much sharper than the closed-capped single tip MWCNT in order to achieve a similar magnitude of emission current. The simulation results also indicate that a space charge effect will occur at high emission currents in the order of 0.1 mA at the simulation conditions of this study. It is also found that the height of the MWCNTs can affect the emission current significantly. For open-ended MWCNTs, smaller diameter MWCNTs will have larger emission currents. On the other hand, for closed-capped MWCNTs, the diameter is not an issue as long as the radius of the curvature of the tip is kept unchanged. One important finding is that the number density of MWCNTs on the substrate can affect the emission current greatly due to the screening effect of nearby MWCNTs. For the simulated 100 and 200 nm height MWCNTs, it is found that the spacing between neighboring MWCNTs should be kept at least larger than 200 nm to avoid serious screening effects.
Electron field emission properties of carbon nanotubes grown on nickel caps
Authors: Cheng Hsiu-Fung , Tsau You-Ming , Chen Yi-Chun , Hsieh Yun-Shuo , Lin I.-Nan
Published: August 2003

Carbon nanotubes (CNTs) were grown on Ni caps, possessing good electron field emission properties and exhibiting good potential for the applications as the electron sources in cathode ray tubes. The characteristies of the CNTs grown on Ni caps vary with the synthesis processes markedly. For the gas-phase-formed CNTs, which were grown on ferrocene-derived Fe clusters via a gas-phase-nucleation process, the CNTs are uniformly small in diameter and of high purity. In contrast, for the surface-grown CNTs, which were formed on Fe(C7H17COO)3-derived Fe clusters, the CNTs are large in diameter, containing large proportion of carbon soots. However, the surface-grown CNTs exhibit markedly better electron field emission capacity (Je)s=4.4 mA/cm2, than the gas-phase-formed CNTs, (Je)g=1.5 mA/cm2 at 22.5 V/μm, even though the latter possess a smaller effective work function [(Φe)s=0.114 eV and (Φe)g=0.034 eV]. Such phenomenon is presumably ascribed to the better CNT-to-substrate contact properties for the CNTs grown directly on the Fe clusters coated on Ni caps.
Investigation of protein adsorption with simultaneous measurements of atomic force microscope and quartz crystal microbalance
Authors: Choi K.-H. , Friedt J.-M. , Laureyn W. , Frederix F. , Campitelli A. , Borghs G.
Published: August 2003

We have combined the tapping-mode atomic force microscope (AFM) and quartz crystal microbalance (QCM) for simultaneous investigation and characterization of protein adsorption on various metallic surfaces using these two instruments. The adsorption of proteins such as human plasma fibrinogen and anti-human immunoglobulin onto the metal or oxide/QCM surface were monitored using both methods at the same time when varying the concentration of proteins. The combination of AFM with QCM allowing the simultaneous measurements with two techniques working at very different scales and probing different properties of the adsorbed layer provides quantitative and qualitative information that can distinguish different protein adsorption behavior.
Self-assembled CoAs nanostructures
Authors: Farrell H. H. , LaViolette Randall A. , Schultz B. D. , Lüdge K. , Palmstrøm C. J.
Published: August 2003

At low coverages, the codeposition of Co and As on the GaAs(100)c(4×4) surface results in the formation of two different types of self-assembled nanostructures; one has a “mesa” configuration, and the other a large aspect ratio “nanostripe” configuration. Minimum-energy calculations have been performed on several possible surface reconstructions for the latter configuration. The favored structure has a rather small unit that repeats essentially endlessly along the [1_10] direction. This unit contains one Co atom substituted between adjacent c(4×4) As dimers that straddle a misfit dislocation in the two-dimensional c(4×4) lattice. The distorted octahedral bonding around these Co atoms is completed by the addition of three As atoms to the repeat unit. A dip or a valley is formed on each side of the nanostripe by removing As atoms from the substrate. This valley partially relieves the compressive strain along the [110] direction across the nanostripes, and it helps to insure that each Co atom is surrounded by the requisite 18 valence electrons. The detailed atomic structure of the mesas was not determined. However, it is suggested that they are CoAs crystallites with a specific orientation relative to the substrate.
Field emission and growth characteristics of carbon nanotubes with optical emission spectroscopy analysis in C3H4 and CO deposition systems
Authors: Han Jae-Hee , Lee Tae Young , Yoo Ji-Beom , Park Chong-Yun , Jung Taewon , Kim Jong Min , Yu SeGi , Yi Whikun
Published: August 2003

Chemical species during growth of carbon nanotubes (CNTs) in direct current-plasma-enhanced chemical vapor deposition were studied in detail using C3H4–NH3 and CO–NH3 mixtures through optical emission spectroscopy. In the C3H4–NH3 system, the relative intensities of CN (388.3 nm) and CH (431.4 nm) decreased and that of C2 (436 nm) increased, leading to sp2 graphization into the CNT structure, leading to improvement of field emission property of CNTs. In the CO–NH3 system, the trend is completely reversed. Attributed to the balance of kinetics involved, CNTs could be grown most effectively under specific conditions. Based on these results, we suggest the growth mechanism and the correlation between morphologies and field emission properties of CNTs in our system.
Selective enhancement filters for nodules, vessels, and airway walls in two‐ and three‐dimensional CT scans
Authors: Li Qiang , Sone Shusuke , Doi Kunio
Published: August 2003

Computer‐aided diagnostic (CAD) schemes have been developed to assist radiologists in the early detection of lung cancer in radiographs and computed tomography (CT) images. In order to improve sensitivity for nodule detection, many researchers have employed a filter as a preprocessing step for enhancement of nodules. However, these filters enhance not only nodules, but also other anatomic structures such as ribs, blood vessels, and airway walls. Therefore, nodules are often detected together with a large number of false positives caused by these normal anatomic structures. In this study, we developed three selective enhancement filters for dot, line, and plane which can simultaneously enhance objects of a specific shape (for example, dot‐like nodules) and suppress objects of other shapes (for example, line‐like vessels). Therefore, as preprocessing steps, these filters would be useful for improving the sensitivity of nodule detection and for reducing the number of false positives. We applied our enhancement filters to synthesized images to demonstrate that they can selectively enhance a specific shape and suppress other shapes. We also applied our enhancement filters to real two‐dimensional (2D) and three‐dimensional (3D) CT images to show their effectiveness in the enhancement of specific objects in real medical images. We believe that the three enhancement filters developed in this study would be useful in the computerized detection of cancer in 2D and 3D medical images.
Analyses and applications of single scan dose profiles in computed tomography
Authors: Tsai H. Y. , Tung C. J. , Huang M. H. , Wan Y. L.
Published: August 2003

Comprehensive analyses and measurements of computed tomography (CT) single‐scan dose profiles were performed for several scanners and operating conditions. Measurements were made using two types of thermoluminescent dosimeters, LiF:Mg,Cu,P and and two CT dosimetry phantoms, head and body. Analyses of CT single‐scan dose profiles were made in terms of a Gaussian function for primary radiation and a Lorentzian function for scattered radiation. This function was used to investigate several common descriptions of the CT dose, including the computed tomography dose index (CTDI) and the multiple scan average dose. The relative percentage of scatter versus primary radiation to the contribution of CTDI at the central and peripheral locations was determined and analyzed. The correlation between CTDI of thermoluminescent dosimeter measurements and pencil‐shaped ionization chamber measurements was determined. A method for estimating organ dose from CT was developed and compared to organ‐dose estimates from Monte Carlo simulations.
Photonuclear dose calculations for high‐energy photon beams from Siemens and Varian linacs
Authors: Chibani Omar , Ma Chang‐Ming Charlie
Published: August 2003

The dose from photon‐induced nuclear particles (neutrons, protons, and alpha particles) generated by high‐energy photon beams from medical linacs is investigated. Monte Carlo calculations using the MCNPX code are performed for three different photon beams from two different machines: Siemens 18 MV, Varian 15 MV, and Varian 18 MV. The linac head components are simulated in detail. The dose distributions from photons, neutrons, protons, and alpha particles are calculated in a tissue‐equivalent phantom. Neutrons are generated in both the linac head and the phantom. This study includes (a) field size effects, (b) off‐axis dose profiles, (c) neutron contribution from the linac head, (d) dose contribution from capture gamma rays, (e) phantom heterogeneity effects, and (f) effects of primary electron energy shift. Results are presented in terms of absolute dose distributions and also in terms of DER (dose equivalent ratio). The DER is the maximum dose from the particle (neutron, proton, or alpha) divided by the maximum photon dose, multiplied by the particle quality factor and the modulation scaling factor. The total DER including neutrons, protons, and alphas is about 0.66 cSv/Gy for the Siemens 18 MV beam The neutron DER decreases with decreasing field size while the proton (or alpha) DER does not vary significantly except for the field. Both Varian beams (15 and 18 MV) produce more neutrons, protons, and alphas particles than the Siemens 18 MV beam. This is mainly due to their higher primary electron energies: 15 and 18.3 MeV, respectively, vs 14 MeV for the Siemens 18 MV beam. For all beams, neutrons contribute more than 75% of the total DER, except for the field The total DER is 1.52 and 2.86 cSv/Gy for the 15 and 18 MV Varian beams respectively. Media with relatively high‐ elements like bone may increase the dose from heavy charged particles by a factor 4. The total DER is sensitive to primary electron energy shift. A Siemens 18 MV beam with 15 MeV (instead of 14 MeV) primary electrons would increase by 40% the neutron DER and by 210% the DER. Comparisons with measurements (neutron yields from different materials and neutron dose equivalent) are also presented. Using the NCRP risk assessment method, we found that the dose equivalent from leakage neutrons (at 50‐cm off‐axis distance) represent 1.1, 1.1, and 2.0% likelihood of fatal secondary cancer for a 70 Gy treatment delivered by the Siemens 18 MV, Varian 15 MV, and Varian 18 MV beams, respectively.
3D dose verification in HDR prostate monotherapy using polymer gels and MRI
Authors: Kipouros P. , Papagiannis P. , Sakelliou L. , Karaiskos P. , Sandilos P. , Baras P. , Seimenis I. , Kozicki M. , Anagnostopoulos G. , Baltas D.
Published: August 2003

VIPAR polymer gels and 3D MRI techniques were evaluated for their ability to provide experimental verification of 3D dose distributions in a simulation of a prostate monotherapy clinical application. A real clinical treatment plan was utilized, generated by post‐irradiation, CT based calculations derived from Plato™ BPS and Swift™ treatment planning systems. The simulated treatment plan involved the use of 10 catheters and 39 source positions within a glass vessel of appropriate dimensions, homogeneously filled with the VIPAR gel. 3D high resolution MR scanning of the gel produced relaxation time maps, from which 3D dose distributions were derived via an appropriate calibration procedure. Results were compared to corresponding dose distributions obtained from the Plato and Swift treatment planning systems. Quantitative comparison, on a point by point basis, was based on user adopted acceptance criteria of 5% dose‐difference and 3 mm distance‐to‐agreement. Significant deviations between experimental and calculated dose distributions were found for doses lower than 50% due to the reduced dose resolution of the method in the low dose, low dose gradient region. Measurement errors were observed at 1.0–1.5 mm around each catheter due to MR imaging susceptibility artifacts. For most remaining points the acceptance criteria were fulfilled. Systematic offsets of the order of 1–2 mm, observed between measured and corresponding calculated isocontours at specific segments, are attributed to the 1 mm uncertainty in catheter reconstruction and 1 mm uncertainty in the alignment of the MR and CT imaging planes.
Diamond detector versus silicon diode and ion chamber in photon beams of different energy and field size
Authors: Bucciolini M. , Banci Buonamici F. , Mazzocchi S. , De Angelis C. , Onori S. , Cirrone G. A. P.
Published: August 2003

The aim of this work was to test the suitability of a PTW diamond detector for nonreference condition dosimetry in photon beams of different energy (6 and 25 MV) and field size (from to Diamond behavior was compared to that of a Scanditronix p‐type silicon diode and a Scanditronix RK ionization chamber. Measurements included output factors (OF), percentage depth doses (PDD) and dose profiles. OFs measured with diamond detector agreed within 1% with those measured with diode and RK chamber. Only at 25 MV, for the smallest field size, RK chamber underestimated OFs due to averaging effects in a pointed shaped beam profile. Agreement was found between PDDs measured with diamond detector and RK chamber for both 6 MV and 25 MV photons and down to field size. For the field size, at 25 MV, RK chamber underestimated doses at shallow depth and the difference progressively went to zero in the distal region. PDD curves measured with silicon diode and diamond detector agreed well for the 25 MV beam at all the field sizes. Conversely, the nontissue equivalence of silicon led, for the 6 MV beam, to a slight overestimation of the diode doses in the distal region, at all the field sizes. Penumbra and field width measurements gave values in agreement for all the detectors but with a systematic overestimate by RK measurements. The results obtained confirm that ion chamber is not a suitable detector when high spatial resolution is required. On the other hand, the small differences in the studied parameters, between diamond and silicon systems, do not lead to a significant advantage in the use of diamond detector for routine clinical dosimetry.