bluuebunny/crossref_metadata_2025 huggingface dataset:
Functional diversity of photosynthesis during drought in a model tropical rainforest – the contributions of leaf area, photosynthetic electron transport and stomatal conductance to reduction in net ecosystem carbon exchange
Authors: RASCHER U. , BOBICH E. G. , LIN G. H. , WALTER A. , MORRIS T. , NAUMANN M. , NICHOL C. J. , PIERCE D. , BIL K. , KUDEYAROV V. , BERRY J. A.
Published: October 2004

The tropical rainforest mesocosm within the Biosphere 2 Laboratory, a model system of some 110 species developed over 12 years under controlled environmental conditions, has been subjected to a series of comparable drought experiments during 2000–2002. In each study, the mesocosm was subjected to a 4–6 week drought, with well‐defined rainfall events before and after the treatment. Ecosystem CO2 uptake rate (Aeco) declined 32% in response to the drought, with changes occurring within days and being reversible within weeks, even though the deeper soil layers did not become significantly drier and leaf‐level water status of most large trees was not greatly affected. The reduced Aeco during the drought reflected both morphological and physiological responses. It is estimated that the drought‐induced 32% reduction of Aeco has three principal components: (1) leaf fall increased two‐fold whereas leaf expansion growth of some canopy dominants declined to 60%, leading to a 10% decrease in foliage coverage of the canopy. This might be the main reason for the persistent reduction of Aeco after rewatering. (2) The maximum photosynthetic electron transport rate at high light intensities in remaining leaves was reduced to 71% for three of the four species measured, even though no chronic photo‐inhibition occurred. (3) Stomata closed, leading to a reduced ecosystem water conductance to water vapour (33% of pre‐drought values), which not only reduced ecosystem carbon uptake rate, but may also have implications for water and energy budgets of tropical ecosystems. Additionally, individual rainforest trees responded differently, expressing different levels of stress and stress avoiding mechanisms. This functional diversity renders the individual response heterogeneous and has fundamental implications to scale leaf level responses to ecosystem dynamics.
Hydraulic architecture of leaf blades: where is the main resistance?
Authors: COCHARD H. , NARDINI A. , COLL L.
Published: October 2004

The hydraulic architecture of Laurus nobilis L. and Juglans regia L. leaves was studied using three different approaches: (1) hydraulic measurements of both intact leaves and of leaves subjected to treatments aimed at removing the extra‐vascular resistance; (2) direct measurements of the vascular pressure with a pressure probe; and (3) modelling the hydraulic architecture of leaf venation system on the basis of measurements of vein densities and conductivities. The hydraulic resistance of leaves (Rleaf) either cut, boiled or frozen–thawed was reduced by about 60 and 85% with respect to control leaves for laurel and walnut, respectively. Direct pressure drop measurements suggested that 88% of the resistance resided outside the vascular system in walnut. Model simulations were in agreement with these results provided vein hydraulic conductance was 0.12–0.28 that of the conductance predicted by Poiseuille's law. The results suggest that Rleaf is dominated by substantial extra‐vascular resistances and therefore contrast with the conclusions of recent studies dealing with the hydraulic architecture of the leaf. The present study confirms the ‘classical’ view of the hydraulic architecture of leaves as composed by a low‐resistance component (the venation) and a high‐resistance component (the mesophyll).
The apparent feed‐forward response to vapour pressure deficit of stomata in droughted, field‐grown Eucalyptus globulus Labill
Authors: MACFARLANE C. , WHITE D. A. , ADAMS M. A.
Published: October 2004

This study tested a multiplicative model of stomatal response to environment for drought‐affected trees of Eucalyptus globulus Labill. growing in southern Australia. The model incorporates a feed‐forward response to vapour pressure deficit of ambient air (δea) and performed well if evaluated using reduced major axis regression and log‐transformed   data.   There   was   strong   evidence   from gas‐exchange data, leaf water potentials and sapflow measurements of the feed‐forward response by stomata to leaf‐to‐air vapour pressure deficit (δel). The response of stomata to δel was irreversible. Stomatal conductance and the rate of net photosynthesis were highly correlated and declined, together with the rate of transpiration, throughout the afternoon as δea increased despite increasing leaf water potentials. The concentration of CO2 inside leaves (ci) increased as stomatal conductance declined indicating increasing non‐stomatal limitations to photosynthesis. The stomatal response to δel of E. globulus in the field is best described as an ‘apparent feed‐forward response’ that probably results from both slowly reversible depression of net photosynthesis and abscisic acid accumulation in guard cells. We suggest that the stomatal response to ci may strengthen the link between photosynthetic capacity and stomatal conductance during leaf drying as a result of either drought or large δ el.
Effect of potassium deficiency on the plasma membrane H+‐ATPase of the wood ray parenchyma in poplar
Authors: AREND M. , MONSHAUSEN G. , WIND C. , WEISENSEEL M. H. , FROMM J.
Published: October 2004

The effect of K+ deficiency on the plasma membrane (PM) H+‐ATPase was studied in young stems of poplar plants (Populus tremula × tremuloides) grown with low or full‐strength K+ supply. Immunological assays using different antibodies were applied to test if K+ deficiency affects the amount of immunodetectable PM H+‐ATPases in the stem tissue. The monoclonal antibody clone 46 E5 B11 revealed an increased abundance of PM H+‐ATPases under conditions of low K+ supply, and immunolabelling experiments showed that this increase was restricted to vessel‐associated cells (VACs) of the wood ray parenchyma. Replacement of the monoclonal antibody by a polyclonal antibody against PM H+‐ATPase gave a specific immunoreactivity on blots as well as tissue sections too, but the labelling intensity showed no difference between plants with low or full‐strength K+ supply. Measurements of extracellular H+ concentrations using non‐invasive, H+‐selective microelectrodes revealed a lowering of the pH at the surface of VACs and an enhancement of net efflux of H+ in plants grown with low K+ supply. The present results indicate an up‐regulation of specific isoforms of the PM H+‐ATPase in VACs under K+‐deficient conditions and suggest a key role for these PM H+‐ATPases in unloading K+ from the xylem stream.
The plastidic nitrite transporter NAR1;1 improves nitrate use efficiency for growth in Chlamydomonas
Authors: MARISCAL V. , REXACH J. , FERNÁNDEZ E. , GALVÁN A.
Published: October 2004

The Chlamydomonas reinhardtii Nar1;1 gene encodes a membrane protein involved in nitrite transport to the chloroplast and is apparently dispensable for nitrate/nitrite‐dependent growth in some conditions (Rexach, Fernández & Galván, Plant Cell 12, 1441–1454, 2000). In the present study the question of when NAR1;1 is required and how it improves nitrate utilization for growth was investigated. Comparative studies were performed with strains Nar1;1+ and Nar1;1– in nitrate media under three experimental conditions. Under continuous light and high CO2 (5%), strains containing or lacking Nar1;1 showed a very similar nitrate‐dependent growth. Under continuous light and low CO2 (air), Nar1;1 allowed a slightly higher growth in nitrate. However, under light/dark cycles and low CO2, the strain having Nar1;1 showed a higher nitrate‐dependent growth and doubled the amount of protein and chlorophyll than the Nar1;1– strain. The activities for nitrate uptake, nitrite and ammonium excretions, nitrate and nitrite reductases, glutamine synthetase (GS), as well as the transcript levels of Nar1;1, Nrt2;1, Nar2, Nrt2;3 and GS1 and GS2 genes were determined under this third condition by trying to understand how NAR1;1 improves nitrate use efficiency. Nitrite and ammonium excretion, which was higher in the strain Nar1;1– than in Nar1;1+, results in an important deregulation in the gene expression of nitrate transporters and cytosolic GS1. These data lead to the proposal that nitrite transport to the chloroplast mediated by NAR1;1 allows a balanced expression of enzymes and transporters for nitrate assimilation, thus optimizing nitrate utilization under the natural condition of light/dark cycles and air.
Oxidant and antioxidant levels in preterm newborns with idiopathic hyperbilirubinaemia
Authors: Turgut M , Başaran O , Çekmen M , Karataş F , Kurt A , Aygün AD
Published: October 2004

Objectives:  Newborns, particulary preterm infants, have limited antioxidant protective capacity. The organism's defence system against reactive oxygen species including vitamins A, E and C, trace element selenium (Se) and enzymes, such as catalase (CAT), superoxide dismutase (SOD), and glutathione peroxidase (GSH‐Px) are essential components of the antioxidant system against the oxidative injury to the cellular membranes of erythrocytes. In this study, our aim was to compare the oxidant nitric oxide (total plasma nitrite level as an indicator of nitric oxide (NO)), antioxidant vitamins and selenium and erythrocyte antioxidant enzymes in premature babies with hyperbilirubinaemia with healthy preterms.

Methods:  Twenty preterm infants with newborn jaundice were included in the study group, while 15 preterm infants without jaundice were enrolled in the control group. We evaluated the mean plasma levels of, respectively, the total nitrite as an indicator of NO, bilirubin, vitamins A, E, C and selenium, and the activity of erythrocyte antioxidant enzymes such as CAT, SOD and GSH‐Px of preterm infants with idiopathic hyperbilirubinaemia and compared to those of the control group.

Results:  The mean plasma total nitrite and total serum bilirubin levels and blood reticulocyte counts of the study group were found to be significantly higher than those of the control group (P < 0.001, P < 0.001 and P < 0.05, respectively). Furthermore, the activity of erythrocyte antioxidant enzymes (all P < 0.001) and the mean plasma levels of the antioxidant vitamins A, E, and C (P < 0.05, P < 0.05 and P < 0.001, respectively) and selenium (P < 0.001) of the study group were all found to be significantly lower than those of the control group.

Conclusion:  We hypothesize that low antioxidants in pretem babies may predispose them to increased oxidative stress, and cause hyperbilirubinaemia.
Hypercalcaemia and hypertransaminasaemia in a child with hyperthyroidism
Authors: Hui WH , Lee CY
Published: October 2004

Abstract:  Hypercalcaemia and hypertransaminasaemia are well recognized and not infrequent findings in hyperthyroidism in adults. Both conditions are seldom reported in children. Here we report the case of a 4‐year‐old girl with hyperthyroidism associated with hypercalcaemia and hypertransaminasaemia which were reversed after euthyroid state was achieved. We recommend that serum calcium and liver function should always be monitored in children with hyperthyroidism.
Accounting Principles, Internal Conflict and the State: The Case of the ICAEW, 1948–1966
Authors: Noguchi Masayoshi , Edwards John Richard
Published: October 2004

The series of Recommendations on Accounting Principles (RoAPs) issued by the Institute of Chartered Accountants in England and Wales (ICAEW) between 1942 and 1969 demonstrated the willingness of a professional accounting body to take a degree of responsibility for the form and content of British corporate financial reports. RoAPs 12 and 15 focused on the enduring problem of whether and how to take account of changing prices when constructing published financial reports. This article reveals disagreement between practising and industrial members in general, concerning how to address this issue, and examines the way in which the Council of the ICAEW sought to resolve this internal conflict within the constraints imposed by the need to be seen to behave in the ‘public interest’. Major discord between the two main categories of membership emerged within the operation of the Taxation and Financial Relations (T&FR) Committee. What were judged by the ICAEW's leadership to be the extreme views of the industrial members were marginalized and suppressed by bypassing the normal channel for designing RoAPs and, instead, formulating them at the higher level of the Parliamentary and Law (P&L) Committee. The conflict between practising and industrial members continued in the period following the publication of RoAP 15, when further attempts were made to tackle the problem of accounting for inflation.
A Methodology for Calculating the Allowance for Loan Losses in Commercial Banks
Authors: Gray Robert P. , Clarke Frank L.
Published: October 2004

Severe disturbances in the financial markets in many countries during the 1980s and 1990s caused many stakeholders to examine whether commercial banks had adequate reserves for future loan losses. In the United States, bank regulators considered an adequate Allowance for Loan Losses a ‘safety and soundness’ issue while the SEC became increasingly concerned over the possibility of banks using the Allowance as a method to ‘manage earnings’. Both regulators demanded more rigorous calculations from banks to support their accounting entries. Also the FASB and the IASB have expressed concerns about a lack of harmonization and convergence in standards. An analysis of measurement standards in the United States, Canada, Japan, the United Kingdom and Australia, as well as by the Basel Committee on Banking Supervision and the IASB, reveals the partially conflicting goals for the Allowance: (a) promote harmonization (IASB), (b) increase transparency (SEC), (c) promote safety and soundness (bank regulators) and (d) maintain reasonable flexibility in recognition of the subjective aspects in determining an appropriate Allowance (bankers). The article offers a methodology which an individual bank may utilize to reconcile the conflicting goals of all interested parties.
Undergraduate experience of clinical procedures in paediatric dentistry in a UK dental school during 1997—2001
Authors: Seddon R. P.
Published: October 2004

Abstract  The aim of this study was to determine the clinical experience of undergraduate students in paediatric dentistry. This was a prospective study in a clinic teaching paediatric dentistry to undergraduates within a UK dental school. Students who graduated between 1997 and 2001 at King's Dental Institute, London, were required to complete a quantitative record of their clinical activity. The mean undergraduate intake for the 5‐year period was 58. Thirty‐six (36) sessions each of 2— h duration were available in the course for the clinical treatment of children (one half day per week), a total of 81 h. The undergraduates assessed and planned treatment for 13.4 patients, 3.6 emergency patients and administered 10.4 local analgesics. The mean number of inhalation sedation administrations increased (1.5—3.3) per student during the 5‐year period. The mean number of procedures performed by undergraduates for primary teeth was 8.1 restorations in glass ionomer or compomer and 1.9 in amalgam, 1.6 pulpotomies and 0.2 preformed crowns. The mean number of procedures for permanent teeth was 24.5 fissure sealants, 2.6 preventive resin restorations, 1.5 amalgams, 1.7 composites, 1.4 incisal edge restorations and 0.8 root canal treatments. For permanent teeth, the trend was towards an increase in the number of preventive resin restorations (1.9—2.8) and composite restorations (1.4—1.9) but a decrease in the number of amalgam restorations (2.1—0.9) during the 5‐year period. Individual students’ clinical experience was very variable. Procedures that were performed more than 10 times were experienced by every student. A procedure performed on average two to four times within a year group would be experienced by only 80—90% of the group and less frequently performed procedures would only have been experienced by a minority of graduates. A large number of patients failed to attend or cancelled appointments representing a loss of 21 h of clinical treatment time per student, about 25% of the total time available for the treatment of children in the clinical course.
Cardiovascular responses to orthostatic stress in healthy altitude dwellers, and altitude residents with chronic mountain sickness
Authors: Claydon V. E. , Norcliffe L. J. , Moore J. P. , Rivera M. , Leon‐Velarde F. , Appenzeller O. , Hainsworth R.
Published: October 2004

High altitude (HA) dwellers have an exceptionally high tolerance to orthostatic stress, and this may partly be related to their high packed cell and blood volumes. However, it is not known whether their orthostatic tolerance would be changed after relief of the altitude‐related hypoxia. Furthermore, orthostatic tolerance is known also to be influenced by the efficiency of the control of peripheral vascular resistance and by the effectiveness of cerebral autoregulation and these have not been reported in HA dwellers. In this study we examined plasma volume, orthostatic tolerance and peripheral vascular and cerebrovascular responses to orthostatic stress in HA dwellers, including some with chronic mountain sickness (CMS) in whom packed cell and blood volumes are particularly large. Eleven HA control subjects and 11 CMS patients underwent orthostatic stress testing, comprising head‐up tilting with lower body suction, at their resident altitude (4338 m) and at sea level. Blood pressure (Portapres), heart rate (ECG), brachial and middle cerebral artery blood velocities (Doppler) were recorded during the test. Plasma volumes were found to be similar in both groups and at both locations. Packed cell and blood volumes were higher in CMS patients than controls. All subjects had very good orthostatic tolerances at both locations, compared to previously published data in lowland dwellers. In CMS patients responses of forearm vascular resistance to the orthostatic stress, at sea level, were smaller than controls (P < 0.05). Cerebral blood velocity was less in CMS than in controls (P < 0.01) and, at sea level, it decreased more than the controls in response to head‐up tilting (P < 0.02). Cerebral autoregulation, assessed from the relationship between cerebral pressure and velocity, was also impaired in CMS patients compared to HA controls, when examined at sea level (P < 0.02). These results have shown that the good orthostatic tolerance seen in high altitude dwellers at altitude is also seen at sea level. There was no difference in orthostatic tolerance between CMS patients, with their exceptionally large blood volumes, and the HA controls. This may be because peripheral vascular and cerebrovascular responses (at least at sea level) are impaired in the CMS patients relative to HA controls. Thus, the advantage of the large blood volume may be offset by the smaller vascular responses.
Reducing Warpage of Printed Circuit Boards by Using Wavy Traces
Authors: Hutapea Parsaoran , Grenestedt Joachim L.
Published: October 2004

Printed circuit boards (PCB’s) often warp when subjected to temperature changes, associated with either the manufacturing process or the usage. In order to reduce the warpage, waviness was introduced in the electric traces. Model PCB’s were manufactured and tested. The elastic stiffnesses of the PCB’s were determined using a coupled experimental-analytical vibration method, whereas coefficient of thermal expansions (CTE’s) and warpage were measured by placing strain-gage instrumented specimens in an environmental chamber and varying the temperature. Unit cell finite element (FE) analyses of PCB’s with both straight and wavy traces were performed to predict thermoelastic behavior. Both experimental tests and numerical analyses conclude that the PCB’s with wavy traces warped approximately 40% to 60% less than the PCB’s with straight traces.
Interfacial Fracture Toughness Measurement of a Ti/Si Interface
Authors: Modi Mitul , Sitaraman Suresh K.
Published: October 2004

Titanium adhesive layers are commonly used in microelectronic and MEMS applications to help improve the adhesion of other metal layers to a silicon substrate. Such Ti/Si interfaces could potentially delaminate under externally applied mechanical loads, thermally induced stresses, or process-induced intrinsic stresses or a combination of these different loads. In order to design against delamination, knowledge of the interfacial fracture toughness of the Ti/Si interface is necessary. However, interfacial fracture toughness data for such interfaces is not widely available in the open literature, in part due to the difficulty in measuring the strength of thin film interfaces. The Modified Decohesion Test (MDT), a new test developed by the authors, has been used to characterize the mode mix dependent interfacial fracture toughness of a Ti/Si interface. In this approach, a highly stressed super layer is used to drive delamination and generate any mode mix at the crack tip. MDT uses the change in crack surface area to vary the available energy per unit area for crack growth and thus to bound the interfacial fracture toughness. Therefore, this technique uses a single sample to measure the interfacial fracture toughness. Since the deformations remain elastic, a mechanics-based solution can be used to correlate test parameters to the energy release rate. Common IC fabrication techniques are used to prepare the sample and execute the test, thereby making the test compatible with current microelectronic or MEMS facilities. Using the MDT, interfacial fracture toughness (Γ) bounds were found for a Ti/Si interface at three mode mixes. At a mode mix of 19.5 deg, 5.97J/m2⩽Γ⩽7.87J/m2, at a mode mix of 23 deg, 9.32J/m2⩽Γ⩽10.42J/m2, and at a mode mix of 30 deg, 12.70J/m2⩽Γ⩽17.02J/m2.
Thermal Management of Transient Power Spikes in Electronics—Phase Change Energy Storage or Copper Heat Sinks?
Authors: Krishnan Shankar , Garimella Suresh V.
Published: October 2004

A transient thermal analysis is performed to investigate thermal control of power semiconductors using phase change materials, and to compare the performance of this approach to that of copper heat sinks. Both the melting of the phase change material under a transient power spike input, as well as the resolidification process, are considered. Phase change materials of different kinds (paraffin waxes and metallic alloys) are considered, with and without the use of thermal conductivity enhancers. Simple expressions for the melt depth, melting time and temperature distribution are presented in terms of the dimensions of the heat sink and the thermophysical properties of the phase change material, to aid in the design of passive thermal control systems. The simplified analytical expressions are verified against numerical simulations, and are shown to be excellent tools for design calculations. The suppression of junction temperatures achieved by the use of phase change materials when compared to the performance with copper heat sinks is illustrated. Merits of employing phase change materials for pulsed power electronics cooling applications are discussed.
Flow and Heat Transfer Characteristics of a Natural Circulation Evaporative Cooling System for Electronic Components
Authors: Honda Hiroshi , Zhang ZhengGuo , Takata Nobuo
Published: October 2004

Experiments were conducted to study the flow and heat transfer characteristics of a natural circulation liquid cooling system for electronic components. The test loop consisted of a horizontal test section, a horizontal evaporator, a vertical tube, a horizontal condenser, a rubber bag attached at the exit of the condenser, a downcomer, a mass flow meter, and a liquid subcooler. The loop height H was set at either 250 or 450 mm. FC-72 was filled in the test loop up to some level of loop height and the upper part was filled with air. During the operation of the cooling system, the rubber bag expanded and stored the mixture of generated vapor and air. Thus the inner pressure was maintained at atmospheric pressure. In the test section, a silicon chip with dimensions of 10×10×0.5 mm3 was attached at the bottom surface of a horizontal duct with dimensions of 10×14 mm2. A smooth chip and four chips with square micro-pin-fins with 150 to 300 μm in fin height were tested. The duct height s was set at 10 mm for most of the experiments. The cases of s=1 and 25 mm were also tested for one of the micro-pin-finned chips. For each H, the average flow rate of FC-72 was correlated well as a function of the static pressure difference between the two vertical tubes. All chips showed the boiling curve similar to that for pool boiling except that the critical heat flux was lower for the natural circulation loop. For all chips tested, the maximum allowable heat flux qmax increased monotonically with increasing liquid subcooling ΔTsub. Comparison of the results for s=1, 10 and 25 mm revealed that the highest qmax was obtained with s=10 mm. The values of qmax for s=1 and 25 mm were 36–46% and 87–90% of that for s=10 mm, respectively. The maximum value of qmax=56 W/cm2 was obtained by one of the micro-pin-finned chips at s=10 mm and ΔTsub=35 K.
Trade-off Design of Extruded Heat Sinks Using Mathematical Optimization
Authors: de Kock D. J. , Visser J. A.
Published: October 2004

Heat sink designers have to balance a number of conflicting parameters to maximize the performance of heat sinks. This multi-parameter problem lends itself naturally to mathematical optimization techniques. The paper illustrates how mathematical optimization techniques combined with a semi-empirical thermal simulation program can be used to construct a trade-off curve (Pareto-optimal set) between the heat sink mass and thermal resistance for a given heat sink configuration. This trade-off curve can be used by the engineer to decide on the optimal heat sink design that is the best compromise between heat sink mass and thermal resistance for the specific application under consideration.
Strain Energy Density Criterion for Reliability Life Prediction of Solder Joints in Electronic Packaging
Authors: Guven I. , Kradinov V. , Tor J. L. , Madenci E.
Published: October 2004

This study concerns the prediction of crack growth rate for solder joints in electronic packages under thermal cycling. The crack growth rate, which is dependent on the intrinsic solder property and the current stress state, is calculated based on the strain energy density criterion. The critical value of the strain energy density represents the intrinsic property of the solder. The comparison of the crack growth predictions with the experimental measurements demonstrates the applicability of the strain energy density criterion for the reliability life prediction of solder joints.
Etching mechanism of MgO thin films in inductively coupled Cl2∕Ar plasma
Authors: Efremov A. M. , Koo Seong-Mo , Kim Dong-Pyo , Kim Kyoung-Tae , Kim Chang-Il
Published: October 2004

The etching mechanism of MgO thin films in Cl2∕Ar plasma was investigated. It was found that the increasing Ar in the mixing ratio of Cl2∕Ar plasma causes nonmonotonic MgO etch rate, which reaches a maximum value at 70%Ar+30%Cl2. Langmuir probe measurement showed the noticeable influence of Cl2∕Ar mixing ratio on electron temperature and electron density. The zero-dimensional plasma model indicated monotonic changes of both densities and fluxes of active species. At the same time, analyses of surface kinetics showed the possibility of nonmonotonic etch rate behavior due to the concurrence of physical and chemical pathways in ion-assisted chemical reaction.
ZnO
synthesis by high vacuum plasma-assisted chemical vapor deposition using dimethylzinc and atomic oxygen
Authors: Barnes Teresa M. , Hand Steve , Leaf Jackie , Wolden Colin A.
Published: October 2004

Zinc oxide thin films were produced by high vacuum plasma-assisted chemical vapor deposition (HVP-CVD) from dimethylzinc (DMZn) and atomic oxygen. HVP-CVD is differentiated from conventional remote plasma-enhanced CVD in that the operating pressures of the inductively coupled plasma (ICP) source and the deposition chamber are decoupled. Both DMZn and atomic oxygen effuse into the deposition chamber under near collisionless conditions. The deposition rate was measured as a function of DMZn and atomic oxygen flux on glass and silicon substrates. Optical emission spectroscopy and quadrupole mass spectrometry (QMS) were used to provide real time analysis of the ICP source and the deposition chamber. The deposition rate was found to be first order in DMZn pressure and zero order in atomic oxygen density. All films demonstrated excellent transparency and were preferentially orientated along the c-axis. The deposition chemistry occurs exclusively through surface-mediated reactions, since the collisionless transport environment eliminates gas-phase chemistry. QMS analysis revealed that DMZn was almost completely consumed, and desorption of unreacted methyl radicals was greatly accelerated in the presence of atomic oxygen. Negligible zinc was detected in the gas phase, suggesting that Zn was efficiently consumed on the substrate and walls of the reactor.
Comment on “Etch characteristics of CeO2 thin film in Ar∕CF4∕Cl2 plasma” [J. Vac. Sci. Technol. A 21, 426 (2003)]
Authors: Paparazzo E.
Published: October 2004

Comments are made on a recent article by Kim, Chang, and Kim [J. Vac. Sci. Technol. A 21, 426 (2003)], which describes the preparation and the x-ray photoemission spectroscopy study of the etching effects produced by Ar-based plasmas of different composition on the surface chemistry of a CeO2 film grown on Si. We discuss some chemical interactions taking place between Ce, Si, and the ambient humidity during the early stages of film deposition, and demonstrate that the many-body effects involved in Ce3d spectra provide a key for better understanding of the etching mechanisms exerted by the plasma treatments.
Relationship between optical properties and microstructure of CeO2–SiO2 composite thin films
Authors: Koo Won Hoe , Jeong Soon Moon , Choi Sang Hun , Koo Baik Hong , Lee Se Jong , Lee Sung Man
Published: October 2004

CeO 2 – SiO 2 composite thin films were prepared by e-beam evaporation and ion beam assisted deposition using an End-Hall ion source. The refractive index of composite thin films exhibited a maximum value at 20%–35%SiO2 fraction, indicating the high packing density. Optical analysis revealed that the transmittance and reflectance spectra of composite films were consistent with the results of the refractive index. The results from x-ray diffractometry, atomic force microscopy and scanning electron microscopy measurements showed that composite thin films containing 20%–35%SiO2 concentration had a dense and smooth amorphous surface, compared to the roughened granular structure of the pure SiO2 and CeO2 thin films. The composite thin films with 20%–35%SiO2 concentration exhibited a higher resistance to water absorption than the CeO2 thin films in spite of the highest refractive index.
Laser-triggered hollow-cathode plasma process for film growth
Authors: Witanachchi S. , Mahawela P. , Mukherjee P.
Published: October 2004

A method of generating a pulsed plasma plume of metallic species using a hollow-cathode arc discharge arrangement is presented. Electrical energy from a pulse-forming network (PFN) generates the transient plasma that evaporates material from the anode that is placed inside a hollow cathode. The discharge is triggered by thermionic electrons produced by a CO2 laser pulse that impinges on one of the electrodes. This plasma process has been used to deposit carbon films in a low-pressure argon or nitrogen ambient. Current pulses of 4–10ms in duration with peak currents of 350A have been produced by the PFN. Characteristics of the produced plasma have been studied by optical emission spectroscopy. The amount of energy imparted to the argon plasma is more than that for a nitrogen plasma. Comparison of on-axis intensity for the 426.9nm line of C+ for the two plasmas shows that the density of carbon ions generated in the nitrogen plasma is higher than that in the argon plasma. Films deposited by this method have fairly uniform thickness profiles that are of the form cos0.4θ for the argon plasma and cos2.2θ for the nitrogen plasma. This indicates that the nitrogen plasma is more forward directed than the argon plasma. Deposition rates of about 10–16Å∕pulse have been obtained for carbon films.
Outgassing measurements of stacked laminations for use as an electromagnet core
Authors: Saito Y. , Sato Y. , Kubo T.
Published: October 2004

Outgassing from an electromagnet core installed in an accelerator vacuum system is a problem, since it causes a poor vacuum, thus shortening the beam lifetime while also inducing electrical breakdown. Outgassing measurements by a throughput method were carried out for stacked laminations with a few types of insulating coatings. The vacuum performance does not always depend on a small conductance in a narrow gap spacing of a few micrometers, but on the materials coated for electrical insulation. A high-temperature cured inorganic and plasma-sprayed ceramic coating shows a lower outgassing rate than a quasi-inorganic one by an order or more. An outgassing reduction effect by a prebaking treatment is also examined. Furthermore, a time lag in the pumpdown characteristic of the stacked laminations is discussed.
Surface wave focusing and acoustic communications in the surf zone
Authors: Preisig James C. , Deane Grant B.
Published: October 2004

The forward scattering of acoustic signals off of shoaling surface gravity waves in the surf zone results in a time-varying channel impulse response that is characterized by intense, rapidly fluctuating arrivals. In some cases, the acoustic focusing by the curvature of the wave crest results in the formation of caustics at or near a receiver location. This focusing and the resulting caustics present challenges to the reliable operation of phase coherent underwater acoustic communications systems that must implicitly or explicitly track the fluctuations in the impulse response. The propagation physics leading to focusing are studied with both experimental data and a propagation model using surface wave profiles measured during the collection of the experimental data. The deterministic experimental and modeled data show good agreement and demonstrate the stages of the focusing event and the impact of the high intensity arrivals and rapid fluctuations on the ability of an algorithm to accurately estimate the impulse response. The statistical characterization of experimental data shows that the focusing by surface gravity waves results in focused surface reflected arrivals whose intensity often exceeds that of the direct arrival and the focusing and caustic formation adversely impacts the performance of an impulse response estimation algorithm.
The effect of surface agitation on ultrasound-mediated gene transfer in vitro
Authors: Chen Wen-Shiang , Lu Xiaochun , Liu Yunbo , Zhong Pei
Published: October 2004

This article reports the effect of surface agitation of culture medium on ultrasound-mediated gene transfection in vitro and its possible mechanisms. The possibility of active induction of bubbles without using contrast microbubbles for effective gene transfer was also demonstrated. Cultured HeLa cells mixed with green fluorescent protein plasmid were exposed to 1.0 MHz ultrasound in 24-well culture plates. Up to 26% transfection efficiency in the survival cell population was achieved in samples exposed to 0.44 MPa ultrasound pulses with the presence of surface agitation. Inertial cavitation and bubble generation were observed throughout the ultrasound exposure. When surface agitation was suppressed by covering the medium surface with a thin membrane, bubble generation and gene transfection were significantly suppressed. Interestingly, transfection efficiency could be partially resumed by adding a small amount of culture medium onto the covering membrane to rebuild the surface agitation and bubble generation. Pressure fluctuation and transient high-pressure loci were found in samples with surface agitation. Numerical simulations of bubble dynamics showed that transient high pressures above the inertial cavitation threshold could generate bubbles, which might be subsequently stabilized at lower pressures by rectified diffusion, and exert strong shear forces that might create transient pores on cell membranes to facilitate gene transfer.
Acoustic directivity of rectangular pistons on prolate spheroids
Authors: Boisvert Jeffrey E. , Van Buren A. L.
Published: October 2004

The directivity of acoustic radiation from a rectangular piston arbitrarily located on a rigid prolate spheroidal baffle is formulated. The piston is assumed to vibrate with uniform normal velocity and the solution is expressed in terms of a modal series representation in spheroidal eigenfunctions. The prolate spheroidal wave functions are obtained using computer programs that have been recently developed to provide accurate values of the wave functions at high frequencies. Results are presented in the form of far-field polar directivity patterns for various piston/spheroid acoustic sizes, piston locations on the spheroid, and spheroidal shapes.
Speech activity detection and enhancement of a moving speaker based on the wideband generalized likelihood ratio and microphone arrays
Authors: Potamitis Ilyas , Fishler Eran
Published: October 2004

The subject of this work is a unifying treatment of estimating the Direction of Arrival (DOA), detecting speech activity and suppressing noise in the case of a moving speaker by using a linear microphone array. The approach is based on the generalized likelihood ratio test applied to the framework of far-field, wideband moving sources (W-GLRT). It is shown that under certain distributional assumptions the W-GLRT provides a framework for the evaluation of DOA measurements against spurious DOAs, probabilistic speech activity detection as well as speech enhancement. As regards speech enhancement, we demonstrate the direct connection of W-GLRT with enhancement based on subspace methods. In addition, through the concept of directive a priori SNR we demonstrate its indirect connection with Minimum Mean Square Error spectral (MMSE_SA) and log-spectral gain modification (MMSE_LSA). The efficiency of the approach is illustrated on a moving speaker when either additive white Gaussian or babble noise is present in the acoustical field at very low SNRs.
Informational masking in hearing-impaired and normal-hearing listeners: Sensation level and decision weights
Authors: Alexander Joshua M. , Lutfi Robert A.
Published: October 2004

Informational masking (IM) refers to elevations in signal threshold caused by masker uncertainty. The purpose of this study was to investigate two factors expected to influence IM in hearing-impaired listeners. Masked thresholds for a 2000-Hz signal in the presence of simultaneous multitone maskers were measured in 16 normal-hearing (NH) and 9 hearing-impaired (HI) listeners. The maskers were 70 dB SPL average total power and were comprised of fixed-frequency components between 522 and 8346 Hz that were separated from each other by at least 13 oct and from the signal by at least 23 octs. Masker uncertainty was manipulated by randomly presenting each masker component with probability p=0.1,0.2,…,0.9, or 1.0 across different trial blocks. Energetic masking was estimated as the amount of masking for p=1.0, where masker uncertainty was minimum. IM was estimated as the amount of masking in excess of energetic masking. Decision weights were estimated by a regression of the listener’s yes/no responses against the presence or absence of the signal and masker components. The decision weights and sensation levels (SLs) of the stimulus components were incorporated as factors in a model that predicts individual differences in IM based on the level variance (in dB) at the output of independent auditory filters [Lutfi, J. Acoust. Soc. Am. 94, 748–758 (1993)]. The results showed much individual variability in IM for the NH listeners (over 40 dB), but little IM for most HI listeners. When masker components were presented to a group of NH listeners at SLs similar to the HI listeners, IM was also similar to the HI listeners. IM was also similar for both groups when the level per masker component was 10 dB SL. These results suggest that reduced masker SLs for HI listeners decrease IM by effectively reducing masker variance. Weighting efficiencies, computed by comparing each listener’s pattern of weights to that of an ideal analytic listener, were a good predictor of individual differences in IM among the NH listeners. For the HI listeners weighting efficiency and IM were unrelated because of the large variation in masker SLs among individual listeners, the small variance in IM, and perhaps because broadened auditory filters in some listeners increased the covariance in auditory filter outputs.
Development of a quick speech-in-noise test for measuring signal-to-noise ratio loss in normal-hearing and hearing-impaired listeners
Authors: Killion Mead C. , Niquette Patricia A. , Gudmundsen Gail I. , Revit Lawrence J. , Banerjee Shilpi
Published: October 2004

This paper describes a shortened and improved version of the Speech in Noise (SIN™) Test (Etymotic Research, 1993). In the first two of four experiments, the level of a female talker relative to that of four-talker babble was adjusted sentence by sentence to produce 50% correct scores for normal-hearing subjects. In the second two experiments, those sentences-in-babble that produced either lack of equivalence or high across-subject variability in scores were discarded. These experiments produced 12 equivalent lists, each containing six sentences, with one sentence at each adjusted signal-to-noise ratio of 25, 20, 15, 10, 5, and 0 dB. Six additional lists were also made equivalent when the scores of particular pairs were averaged. The final lists comprise the “QuickSIN” test that measures the SNR a listener requires to understand 50% of key words in sentences in a background of babble. The standard deviation of single-list scores is 1.4 dB SNR for hearing-impaired subjects, based on test-retest data. A single QuickSIN list takes approximately one minute to administer and provides an estimate of SNR loss accurate to ±2.7 dB at the 95% confidence level.
Side effects of fast-acting dynamic range compression that affect intelligibility in a competing speech task
Authors: Stone Michael A. , Moore Brian C. J.
Published: October 2004

Using a cochlear implant simulator, Stone and Moore [J. Acoust. Soc. Am. 114, 1023–1034 (2003)] reported that wideband fast-acting compression led to poorer intelligibility than slow-acting compression in a competing speech task. Compression speed was varied by using different pairs of attack and release times. In the first experiment reported here, it is shown that attack times less than about 2 ms in a wideband compressor are deleterious to intelligibility. In experiment 2, fast wideband compression was applied to the target and background either before or after mixing. The former reduced the modulation depth of each signal but maintained the independence between the two signals, while the latter introduced “comodulation.” Using simulations with 6 and 11 channels, intelligibility was higher when compression was applied before mixing. In experiment 3, wideband compression was compared with multichannel compression; the latter led to reduced comodulation effects. For 6 channels, the position of the compressor, either wideband or within each channel, had no effect on intelligibility. For 11 channels, channel compression severely degraded intelligibility compared to wideband compression, presumably because of the greater reduction of across-channel contrasts. Overall, caution appears necessary in the use of fast-acting compression in cochlear implants, so as to preserve intelligibility.
The control of aerodynamics, acoustics, and perceptual characteristics during speech production
Authors: Huber Jessica E. , Stathopoulos Elaine T. , Sussman Joan E.
Published: October 2004

One of the most important areas of study in speech motor control is the identification of control variables, the variables controlled by the nervous system during motor tasks. The current study examined two hypotheses regarding control variables in speech production: (1) pressure and resistance in the vocal tract are controlled, and (2) perceptual and acoustic accuracy are controlled. Aerodynamic and acoustic data were collected on 20 subjects in three conditions, normally (NT), with an open air pressure bleed tube in place (TWB), and with a closed bleed tube in place (TNB). The voice recordings collected from the speakers in the production study were used in the perceptual study. Results showed that oral pressure (Po) was significantly lower in the TWB condition than in the NT and TNB conditions. The Po in the TWB condition seemed to be related to maintenance of subglottal pressure (Ps). Examination of the perceptual and acoustic data indicated that perceptual accuracy for [ɑ] was achieved by maintaining Ps to preserve a steady sound pressure level, fundamental frequency, and voicing. Overall, it appeared speakers controlled pressure in compensating, but for the ultimate goal of maintaining acoustic and perceptual accuracy.
Submerged plane layered isotropic media: Properties of the scattering matrix eigenvalues with application to bilayers (L)
Authors: Franklin Hervé , Izbicki Jean-Louis , Marie-Françoise Teddy , Rembert Pascal
Published: October 2004

The plot of the transmission coefficient moduli cannot be used to analyze all the resonances of layered structures because of the overlapping of the resonances. A method using the scattering matrix eigenvalues is presented. It allows, first, to annihilate the overlapping and to recover the resonance positions and half-widths and second, to divide in two independent sets most of the resonances involved in symmetric structures as well as in nonsymmetric ones. Comparisons between the results provided by the method and those coming from the poles of the transmission coefficient agree. In many cases, the transition terms constitute a generalization of the transmission coefficients.
Examination of coherent surface reflection coefficient (CSRC) approximations in shallow water propagation
Authors: Williams Kevin L. , Thorsos Eric I. , Elam W. T.
Published: October 2004

The parabolic wave equation (PE) code of Rosenberg [J. Acoust. Soc. Am. 105, 144–153 (1999)] is used as a benchmark to study acoustic propagation in an ocean waveguide with a rough air/water interface. The PE results allow a close examination of the ability of a ray code [i.e., Gaussian RAy Bundle (GRAB)] to accurately estimate coherent field propagation using a coherent reflection coefficient derived from scattering theory. Comparison with PE implies that the Beckmann–Spizzichino model, as given within the GRAB software package, does not give accurate predictions of the coherent field at long ranges. Three other coherent reflection coefficient approximations are tested: the perturbation, the small slope, and the Kirchhoff approximations. The small slope approximation is the most accurate of the models tested. However, the Kirchhoff approximation is perhaps accurate enough for some purposes and would be simpler to implement as a module within GRAB.
Time-domain equations for sound propagation in rigid-frame porous media (L)
Authors: Wilson D. Keith , Ostashev Vladimir E. , Collier Sandra L.
Published: October 2004

A general set of time-domain equations describing linear sound propagation in a rigid-frame, gas-saturated porous medium is derived. The equations, which are valid for all frequencies, are based on a relaxational model for the viscous and thermal diffusion processes occuring in the pores. The dissipative terms in the equations involve convolutions of the acoustic fields with the impulse response of the medium. It is shown that the equations reduce to previously known results in the limits of low and high frequencies. Alternative time-domain equations are also derived based on a Padé approximation.