bluuebunny/crossref_metadata_2025 huggingface dataset:
A Scalable Approach to Interactive Global Illumination
Authors: Benthin Carsten , Wald Ingo , Slusallek Philipp
Published: November 2003

The addition of global illumination can dramatically increase the realism achievable when rendering virtual environments.In particular with interactive applications we expect the environment to reflect changes in the scenedue to global lighting effects instead of it being just a static backdrop. However, a sufficiently fast and accuratecomputation of global illumination at interactive rates has been difficult even with recent approaches based onrealtime ray tracing.

In this paper we present a highly scalable approach to interactive global illumination. It fully recomputes a high‐qualitysolution for each frame and thus offers immediate feedback even for dynamic scenes, achieving more than20 fps for simple scenes. Compared to previous systems we increased the raw performance by a factor of up toeight and removed the bottlenecks that were limiting scalability. The system now scales linearly in quality andavailable computing resources, tested with up to 48 CPUs in a commodity PC‐cluster. Due to its logarithmicscaling property with respect to scene complexity it even supports lighting simulation in complex scenes with morethan 50 million triangles. This scalability allows applications to perform flexible performance trade‐offs. We alsoargue that the realism achievable through interactive global illumination will make it a standard feature of future3D graphics systems once the required computing resources are readily available.
Visyllable Based Speech Animation
Authors: Kshirsagar Sumedha , Magnenat‐Thalmann Nadia
Published: November 2003

Visemes are visual counterpart of phonemes. Traditionally, the speech animation of 3D synthetic faces involvesextraction of visemes from input speech followed by the application of co‐articulation rules to generate realisticanimation. In this paper, we take a novel approach for speech animation — using visyllables, the visual counterpartof syllables. The approach results into a concatenative visyllable based speech animation system. The key contributionof this paper lies in two main areas. Firstly, we define a set of visyllable units for spoken English along withthe associated phonological rules for valid syllables. Based on these rules, we have implemented a syllabificationalgorithm that allows segmentation of a given phoneme stream into syllables and subsequently visyllables. Secondly,we have recorded the database of visyllables using a facial motion capture system. The recorded visyllableunits are post‐processed semi‐automatically to ensure continuity at the vowel boundaries of the visyllables. We defineeach visyllable in terms of the Facial Movement Parameters (FMP). The FMPs are obtained as a result of thestatistical analysis of the facial motion capture data. The FMPs allow a compact representation of the visyllables.Further, the FMPs also facilitate the formulation of rules for boundary matching and smoothing after concatenatingthe visyllables units. Ours is the first visyllable based speech animation system. The proposed technique iseasy to implement, effective for real‐time as well as non real‐time applications and results into realistic speechanimation.

Categories and Subject Descriptors (according to ACM CCS): 1.3.7 [Computer Graphics]: Three‐Dimensional Graphics and Realism
Narrative Use of Sign Language by a Virtual Character for the Hearing Impaired
Authors: Rieger Thomas , Braun Norbert
Published: November 2003

This paper describes the concept and control of a 3d virtual character system with facial expressions and gesturesas a conversational user interface with narrative expressiveness for the hearing impaired. The gestures and facialexpressions are based on morphing techniques. The system allows the generation of sign language and mouthmotion in real time from text at the level of lip reading quality. The concept of Narrative Extended Speech Acts(NESA) is introduced, based on Interactive Storytelling techniques and the concepts of Narrative Conflict andSuspense Progression. We define a choice of annotation tags to be used with NESAs. We use the NESAs to classifyconversation fragments and to enhance computer generated sign language. We note, how the sign language gesturesare generated and show the possibilities for editing sign language gestures. Furthermore, we give details onhow the NESAs are mapped to gestures. We show the possibilities of controlling the virtual character's behaviourand gestures in a human‐oriented way and provide an outlook on future work.

Categories and Subject Descriptors (according to ACM CCS): 1.3.6 [Computer Graphics]: Methodology and Techniques
Interactive Cutaway Illustrations
Authors: Diepstraten J. , Weiskopf D. , Ertl T.
Published: November 2003

In this paper we discuss different approaches to generate cutaway illustrations. The purpose of such a drawingis to allow the viewer to have a look into an otherwise solid opaque object. Traditional methods to draw thesekinds of illustrations are evaluated to extract a small and effective set of rules for a computer‐based renderingof cutaway illustrations. We show that our approaches are not limited to a specific rendering style but can besuccessfully combined with a great variety of well‐known artistic or technical illustration techniques. All methodsof this paper make use of modern graphics hardware functionality to achieve interactive frame rates.
The 1997 Election: Can an Improving Economy Secure a Fifth Tory Term?
Authors: Price Simon
Published: November 2003

The current government is in deep electoral trouble. Nothing is certain in politics, but it still seems very likely the Tories will be defeated by New Labour this spring. Yet the economy is in fine shape – inflation and interest rates are at historically low levels, economic growth is proceeding at a respectable rate, and unemployment continues to fall. Why won’t the electorate reward the government? In this article Simon Price argues that the Tories lost their reputation for economic competence in 1992 and this has swayed the public’s opinion.
Raising Standards in our Schools: Does Class Size Really Matter?
Authors: Vignoles Anna
Published: November 2003

In this article Anna Vignoles reports the results of a recent research project which evaluated the effects of class size and expenditure per pupil in secondary schools on students’ academic performance and their subsequent earnings. Controversially she concludes that simply providing secondary schools with more resources is not likely to improve student outcomes, although increasing class sizes dramatically would almost certainly have a negative impact. The implication of this research is that attention should be focused on identifying the characteristics and management strategies of successful secondary schools.
Are the Official Estimates of Productivity Growth Giving the MPC Misleading Signals?
Authors: Robson Paul , Blake Neil
Published: November 2003

Official estimates show that manufacturing productivity growth has stalled over the past few years, while average earnings have continued to rise. Should these developments worry the Monetary Policy Committee (MPC)? In this article, Neil Blake and Paul Robson argue that employment changes and to a lesser extent output, have been mis‐recorded. It turns out that productivity has been underestimated, with new estimates more consistent with the high average earnings growth data seen recently. Manufacturers have therefore been unnecessarily targeted by the MPC, while other evidence suggests that the service sector is the guilty party.
The Pivotal Role of the ECB in the New Europe
Authors: Allsopp Christopher , Vines David
Published: November 2003

With the successful launch of EMU at the beginning of January 1999, the key question is how well the new grouping of 11 countries – Euroland – will perform macroeconomically. Strains and difficulties between countries appear solvable if the context is a healthy growing Europe, but are more dangerous if the group as a whole performs badly. In this article Christopher Allsopp and David Vines argue that the European Central Bank has a pivotal role. This is not just for the obvious reason, enshrined in the Treaty, that the independent Bank is charged with ensuring price stability. Beyond that, the ECB will necessarily be the main co‐ordinating institution for macroeconomic policy. The single monetary authority interacts, for good or ill, with eleven national governments, eleven fiscal authorities and eleven national labour markets. The game is rigged in an unfamiliar way.
Evaluating the Monetary Policy Committee
Authors: Budd Alan
Published: November 2003

The Bank of England’s Monetary Policy Committee has now been in operation for two years. How can one judge whether it is performing its tasks successfully? In this article Alan Budd considers some of the difficulties in answering what might appear to be a straightforward question.
How Psychological Science Informs the Teaching of Reading
Authors: Rayner Keith , Foorman Barbara R. , Perfetti Charles A. , Pesetsky David , Seidenberg Mark S.
Published: November 2003

This monograph discusses research, theory, and practice relevant to how children learn to read English. After an initial overview of writing systems, the discussion summarizes research from developmental psychology on children's language competency when they enter school and on the nature of early reading development. Subsequent sections review theories of learning to read, the characteristics of children who do not learn to read (i.e., who have developmental dyslexia), research from cognitive psychology and cognitive neuroscience on skilled reading, and connectionist models of learning to read. The implications of the research findings for learning to read and teaching reading are discussed. Next, the primary methods used to teach reading (phonics and whole language) are summarized. The final section reviews laboratory and classroom studies on teaching reading. From these different sources of evidence, two inescapable conclusions emerge: (a) Mastering the alphabetic principle (that written symbols are associated with phonemes) is essential to becoming proficient in the skill of reading, and (b) methods that teach this principle directly are more effective than those that do not (especially for children who are at risk in some way for having difficulty learning to read). Using whole-language activities to supplement phonics instruction does help make reading fun and meaningful for children, but ultimately, phonics instruction is critically important because it helps beginning readers understand the alphabetic principle and learn new words. Thus, elementary-school teachers who make the alphabetic principle explicit are most effective in helping their students become skilled, independent readers.
Revisiting Norton Long's Ecology of Games: A Network Approach
Authors: Cornwell Benjamin , Curry Timothy J. , Schwirian Kent. P.
Published: November 2003

Because the ecology of games (Long, 1958) is generally a qualitative perspective, it rarely has been applied as a means of empirically analyzing the management of community affairs. Here we pair the perspective's emphasis on key actors' goals with a conceptualization of local issues as reference points for the structure of local games. To illustrate, we examine the building of Paul Brown Stadium in Cincinnati, Ohio, in the 1990s using this approach. We treat connections among the actors involved in the affair, the games in which they were involved, and the stadium‐related issues they addressed as three‐mode network data. We use multidimensional scaling and network‐based measures to generate a picture of the structure of the ecology of games relative to the stadium affair. We find that a relational treatment of the ecology of games helps us understand the structure and process of community affairs, and enhances the descriptive utility of Long's perspective.
Quantal transmission at mossy fibre targets in the CA3 region of the rat hippocampus
Authors: Lawrence J. Josh , Grinspan Zachary M. , McBain Chris J.
Published: November 2003

Recent anatomical evidence that inhibitory interneurones receive approximately 10 times more synapses from mossy fibres than do principal neurones (Acsády et al. 1998) has led to the re‐examination of the extent to which interneurones are involved in CA3 network excitability. Although many of the anatomical and physiological properties of mossy fibre–CA3 interneurone synapses have been previously described (Acsády et al. 1998; Tóth et al. 2000), an investigation into the quantal nature of transmission at this synapse has not yet been conducted. Here, we employed variance–mean (VM) analysis to compare the release probability, quantal size (q) and number of release sites (n) at mossy fibre target neurones in CA3. At six of seven interneurone synapses in which a high concentration of Ca2+ was experimentally imposed, the variance–mean relationship could be approximated by a parabola. Estimates of n were 1–2, and the weighted release probability in normal Ca2+ conditions ranged from 0.34 to 0.51. At pyramidal cell synapses, the variance–mean relationship approximated a linear relationship, suggesting that release probability was significantly lower. The weighted quantal amplitude was similar at interneurone synapses and pyramidal cell synapses, although the variability in quantal amplitude was larger at interneurone synapses. Mossy fibre transmission at CA3 interneurone synapses can be explained by a lower number of release sites, a broader range of release probabilities, and larger range of quantal amplitudes than at CA3 pyramidal synapses. Finally, quantal events on to interneurones elicited spike transmission, owing in part to the more depolarized membrane potential than pyramidal cells. These results suggest that although mossy fibre synapses on to pyramidal cells are associated with a larger number of release sites per synapse, the higher connectivity, higher initial release probability, and larger relative impact per quantum on to CA3 interneurones generate strong feedforward inhibition at physiological firing frequencies of dentate granule cells. Given the central role of CA3 interneurones in mossy fibre synaptic transmission, these details of mossy fibre synaptic transmission should provide insight into CA3 network dynamics under both physiological and pathophysiological circumstances.
Recovery of the human photopic electroretinogram after bleaching exposures: estimation of pigment regeneration kinetics
Authors: Mahroo O. A. R. , Lamb T. D.
Published: November 2003

We used a fibre electrode in the lower conjunctival sac of the human eye to record the a‐wave of the photopic electroretinogram elicited in response to dim red flashes, delivered in the presence of a rod‐saturating blue background, before and after exposure of the eye to bright white illumination that bleached a significant fraction of cone photopigment. Responses were recorded from two normal subjects whose pupils were maximally dilated. A range of intensities of bleaching light were used, from 500 to 3000 photopic cd m−2, and exposures were made sufficiently long in duration to achieve a steady‐state bleach. In addition, responses were also recorded following shorter durations of exposures to the highest intensity (3000 cd m−2); these durations ranged from 5 to 60 s. The amplitude of the a‐wave response to dim flashes was reduced following the exposures, with brighter or longer exposures causing greater reduction. The amplitude then recovered within about 4 min to the prebleach level. The amplitudes measured at ca 15 ms after the flash were used to derive the effective intensity of the flashes, thereby quantifying the fraction of photopigment available at the time of delivery of each flash. Recovery from all exposures in both subjects followed a common time course, which could be described well by a model of pigment kinetics based on rate‐limited regeneration, where the initial rate of recovery following a total bleach was ca 50% of the total pigment per minute, and the residual pigment level for half the maximal rate was ca 20% of the total pigment. The same parameters, together with a fixed photosensitivity, could account for the steady‐state pigment levels seen at each bleaching intensity, and also for the fraction of pigment bleached following exposures of different duration at the highest intensity. The dim‐flash ERG thus provides a novel method for assessing pigment regeneration in vivo. Our finding that pigment regeneration follows rate‐limited kinetics may explain previous reports of pigment regeneration deviating from first order kinetics. We present a model of regeneration in which the rate limit arises from a limitation in the delivery of 11‐cis‐retinoid to the photoreceptor outer segments.
Epileptiform activity in rat hippocampus strengthens excitatory synapses
Authors: Abegg Mathias H. , Savic Nataŝa , Ehrengruber Markus U. , McKinney R. Anne , Gähwiler Beat H.
Published: November 2003

Although epileptic seizures are characterized by excessive excitation, the role of excitatory synaptic transmission in the induction and expression of epilepsy remains unclear. Here, we show that epileptiform activity strengthens excitatory hippocampal synapses by increasing the number of functional (RS)‐α‐amino‐3hydroxy‐5methyl‐4‐isoxadepropionate (AMPA)‐type glutamate receptors in CA3–CA1 synapses. This form of synaptic strengthening occludes long‐term potentiation (LTP) and enhances long‐term depression (LTD), processes involved in learning and memory. These changes in synaptic transmission and plasticity, which are fully blocked with N‐methyl‐D‐aspartate (NMDA) receptor antagonists, may underlie epilepsy induction and seizure‐associated memory deficits.
Calmodulin kinase is functionally targeted to the action potential plateau for regulation of L‐type Ca2+ current in rabbit cardiomyocytes
Authors: Wu Yuejin , Kimbrough John T. , Colbran Roger J. , Anderson Mark E.
Published: November 2003

L‐type Ca2+ current (ICa−L) triggers Ca2+ release from the sarcoplasmic reticulum (SR) and both SR and ICa−L are potential sources of intracellular Ca2+ (Ca2+i) for feedback regulation of ICa−L. Ca2+i bound to calmodulin (Ca2+–CaM) can inhibit ICa−L, while Ca2+–CaM can also activate Ca2+–CaM‐dependent protein kinase II (CaMK) to increase ICa. However, it is not known whether ICa−L or the SR is the primary source of Ca2+ for ICa−L regulation. The L‐type Ca2+ channel C terminus is implicated as a critical transduction element for ICa−L responses to Ca2+–CaM and CaMK, and the C terminus undergoes voltage‐dependent steric changes, suggesting that Ca2+i control of ICa−L may also be regulated by cell membrane potential. We developed conditions to separately test the relationship of Ca2+–CaM and CaMK to ICa−L and SR Ca2+i release during voltage clamp conditions modelled upon time and voltage domains relevant to the cardiac action potential. Here we show that CaMK increases ICa−L after brief positive conditioning pulses, whereas Ca2+–CaM reduces ICa−L over a broad range of positive and negative conditioning potentials. SR Ca2+ release was required for both Ca2+–CaM and CaMK ICa−L responses after strongly positive conditioning pulses (+10 and +40 mV), while Ca2+i from ICa−L was sufficient for Ca2+–CaM during weaker depolarizations. These findings show that ICa−L responses to CaMK are voltage dependent and suggest a new model of L‐type Ca2+ channel regulation where voltage‐dependent changes control ICa−L responses to Ca2+–CaM and CaMK signalling.
Mini‐dystrophin restores L‐type calcium currents in skeletal muscle of transgenic mdx mice
Authors: Friedrich O. , Both M. , Gillis J. M. , Chamberlain J. S. , Fink R. H. A.
Published: November 2003

L‐type calcium currents (iCa) were recorded using the two‐microelectrode voltage‐clamp technique in single short toe muscle fibres of three different mouse strains: (i) C57/SV129 wild‐type mice (wt); (ii) mdx mice (an animal model for Duchenne muscular dystrophy; and (iii) transgenically engineered mini‐dystrophin (MinD)‐expressing mdx mice. The activation and inactivation properties of iCa were examined in 2‐ to 18‐month‐old animals. Ca2+ current densities at 0 mV in mdx fibres increased with age, but were always significantly smaller compared to age‐matched wild‐type fibres. Time‐to‐peak (TTP) of iCa was prolonged in mdx fibres compared to wt fibres. MinD fibres always showed similar TTP and current amplitudes compared to age‐matched wt fibres. In all three genotypes, the voltage‐dependent inactivation and deactivation of iCa were similar. Intracellular resting calcium concentration ([Ca2+]i) and the distribution of dihydropyridine binding sites were also not different in young animals of all three genotypes, whereas iCa was markedly reduced in mdx fibres. We conclude, that dystrophin influences L‐type Ca2+ channels via a direct or indirect linkage which may be disrupted in mdx mice and may be crucial for proper excitation–contraction coupling initiating Ca2+ release from the sarcoplasmic reticulum. This linkage seems to be fully restored in the presence of mini‐dystrophin.
Ovine feto‐placental metabolism
Authors: Ward J. W. , Wooding F. B. P. , Fowden A. L.
Published: November 2003

Fetal growth depends on the transplacental nutrient supply, which, in turn, is determined partially by the consumption and production of nutrients by the uteroplacental tissues. In fetal sheep, the rates of growth and umbilical glucose uptake decline coincidently towards term in parallel with the normal prepartum rise in plasma cortisol. While cortisol is known to reduce growth in fetal sheep, its effects on the uteroplacental handling and delivery of nutrients remain unknown. Hence, this study, quantified the rates of umbilical uptake and uteroplacental consumption of nutrients in preterm fetuses infused with cortisol for 5 days to mimic the prepartum cortisol surge. Umbilical uptakes of glucose and lactate, but not oxygen, were significantly lower in cortisol‐ than saline‐infused fetuses, irrespective of whether values were expressed as absolute or weight‐specific rates. The rate of uteroplacental consumption of glucose, but not oxygen, was significantly higher in cortisol‐ than saline‐infused animals. Absolute rates of uteroplacental lactate production were lower in cortisol‐infused animals. When all data were combined, fetal plasma cortisol levels were positively correlated to uteroplacental glucose consumption and inversely related to umbilical glucose uptake. Cortisol treatment had no apparent effect on placental mRNA expression for the glucose transporters, GLUT‐1 and GLUT‐3. The results demonstrate that cortisol is physiological regulator of uteroplacental metabolism and nutrient delivery to the sheep fetus. These observations have important implications for fetal growth both in late gestation and during adverse intrauterine conditions, which raise fetal cortisol levels earlier in gestation.
Activation of the store‐operated calcium current ICRAC can be dissociated from regulated exocytosis in rat basophilic leukaemia (RBL‐1) cells
Authors: Bakowski Daniel , Burgoyne Robert D. , Parekh Anant B.
Published: November 2003

In many cell types, the emptying of intracellular Ca2+ stores results in the opening of store‐operated Ca2+ channels in the plasma membrane. However, the nature of the signal that couples store content to the opening of these Ca2+ channels is unclear. One model proposes that the Ca2+ channels are initially stored in cytoplasmic vesicles but inserted into the plasma membrane upon store depletion via a regulated exocytoytic mechanism (vesicular fusion model). Using the whole‐cell patch‐clamp technique to measure the store‐operated Ca2+ current ICRAC and the capacitance method to monitor vesicular fusion, an indicator of exocytosis, we have investigated the effects of interfering with regulated exocytosis on the ability of ICRAC to activate. We find that the recombinant protein α‐SNAP1–285, an inhibitor of exocytosis in many systems, suppresses such fusion but has no impact on the activation of ICRAC. A variety of other manoeuvres that interfere with vesicle trafficking and exocytosis were also without effect on ICRAC. Impairing constitutive exocytosis with brefeldin A reduced the extent of ICRAC, but this effect was less pronounced when current density was considered instead. Activation of ICRAC can therefore be clearly dissociated from an exocytotic mechanism, a finding that is not easily reconcilable with the vesicular fusion model.
The hippocampal intrinsic network oscillator
Authors: Fischer Yacov
Published: November 2003

Oscillatory activity characterizes the activity of the hippocampus in vivo; however, the underlying mechanism remains unknown. It is also known that during oscillations the number of action potentials provided by the principal cells is surprisingly low, and it is still an open question how oscillations can emerge under such constraints. One suggestion is that the discharge activity of inhibitory cells takes this function; however, this has been found, in my previous studies, not to be the case for cholinergically mediated and intrinsically generated hippocampal oscillations. This study identifies the hippocampal intrinsic network oscillator and the interactions which underlie the concurrent expression of cholinergically mediated theta (4–15 Hz) and gamma (20–80 Hz) oscillations. A particular axonal network that involves the hippocampal associative pathway, shown to consist of axonal collaterals of CA2 and some CA3 pyramidal cells, forms the oscillator core element. It is functionally activated via two cholinergically mediated reactions. First, direct activation of CA2 and CA3 pyramidal cells to discharge. Second, enhancement of gap junction‐mediated axo‐axonic interactions among axons of the core element and associated axons of interneurones, which together form the full oscillator. With these two reactions it is possible to explain the rhythmicities and patterns of activity, under the condition of a low number of action potentials. The discharge of CA3 pyramidals serves mainly as a trigger, while firing by CA2 pyramidals, and to a lesser degree by CA3 pyramidals, maintains the oscillatory activity. The cholinergically mediated 2‐fold increase in axonal gap junction communication between cells serves two functions: (a) creation of specific activation pathways to produce the rhythmicities and patterns, and (b) formation of a reverberatory system that extends the time during which the sparsely generated action potentials can interact in the network, thereby providing a new source of action potentials, critical for the expression of oscillatory activity.
β2‐adrenergic regulation of ciliary beat frequency in rat bronchiolar epithelium: potentiation by isosmotic cell shrinkage
Authors: Shiima‐Kinoshita Chisa , Min Kyong‐Yob , Hanafusa Toshiaki , Mori Hiroshi , Nakahari Takashi
Published: November 2003

Single bronchiolar ciliary cells were isolated from rat lungs. The β2‐adrenergic regulation of ciliary beat frequency (CBF) was studied using video‐optical microscopy. Terbutaline (a β2‐adrenergic agonist) increased CBF in a dose‐dependent manner, and it also decreased the volume of the ciliary cells. These terbutaline actions were inhibited by a PKA inhibitor (H‐89) and mimicked by forskolin, IBMX and DBcAMP. Ion transport inhibitors were used to isosmotically manipulate the volume of the terbutaline‐stimulated bronchiolar ciliary cells. Amiloride (1 μm) and bumetanide (20 μm) potentiated cell shrinkage and the CBF increase, and they shifted the terbutaline dose–response curve to the lower‐concentration side. Quinidine (500 μm), in contrast, increased cell volume and suppressed the CBF increase. Moreover, a KCl solution containing amiloride (1 μm) and strophanthidin (100 μm) increased cell volume and suppressed the CBF increase, and then the subsequent removal of either amiloride or strophanthidin decreased cell volume and further increased CBF. NPPB (10 μm) or glybenclamide (200 μm) had no effect on the action of terbutaline. Thus, in terbutaline‐stimulated ciliary cells, cell shrinkage enhances the CBF increase; in contrast, cell swelling suppresses it. However, the results of direct manupulation of cell volume by applying osmotic stresses (hyperosmotic shrinkage or hyposmotic swelling) were the opposite of the findings of the isosmotic experiments: hyposmotic cell swelling enhanced the CBF increase, while isosmotic swelling suppressed it. These results suggest that isosmotic and non‐isosmotic volume changes in terbutaline‐stimulated bronchiolar ciliary cells may trigger different signalling pathways. In conclusion, terbutaline increases CBF and decreases the volume of rat bronchiolar ciliary cells via cAMP accumulation under isosmotic conditions, and the isosmotic cell shrinkage enhances the CBF increase by increasing cAMP sensitivity.
Large Axisymmetric Deformations of Elastic/Plastic Perforated Circular Plates
Authors: Wu D. , Peddieson J. , Buchanan G. R. , Rochelle S. G.
Published: November 2003

A mathematical model of axisymmetric elastic/plastic perforated circular plate bending and stretching is developed which accounts for through thickness yielding, through thickness variations in perforation geometry, elastic outer edge restraint, and moderately large deflections. Selected numerical solutions of the resulting differential equations are presented graphically and used to illustrate interesting trends.
Lateral loss and dose discrepancies of multileaf collimator segments in intensity modulated radiation therapy
Authors: Cheng Chee W. , Das Indra J. , Huq M. Saiful
Published: November 2003

In the step‐and‐shoot technique delivery of intensity modulated radiation therapy (IMRT), each static field consists of a number of beamlets, some of which may be very small. In this study, we measured the dose characteristics for a range of field sizes: to for 6 and 15 MV x rays. For a given field length, a number of treatment fields are set up by sequentially increasing the field width using a multi leaf collimator. A set of fields is delivered with the accelerator operated in the IMRT mode. Using an ion chamber, the output factors at 1 cm and 3 cm laterally from a field edge are measured at different depths in a solid water phantom. Our results show that with insufficient lateral distance in at least one direction, the absorbed dose never reaches the equilibrium values, and can be significantly lower for very small field sizes. For example, the output factor of the field relative to at is 0.832 and 0.790 for 6 MV and 15 MV x rays, respectively. Multiple output factor curves are obtained for different field lengths and different buildup conditions. Thus under nonequilibrium conditions, output factors are critically dependent on the field size and the conventional method of determining the equivalent square does not apply. Comparison of output factors acquired in the commissioning of the accelerator with those measured in the present study under conditions of nonequilibrium shows large discrepancies between the two sets of measurements. Thus monitor units generated by a treatment planning system using beam data commissioned with symmetric fields may be underestimated by depending on the size and shape of the segments. To facilitate manual MU calculation as an independent check in step‐and‐shoot IMRT, the concept of effective equivalent square (EES) is introduced. Using EES, output factors can be calculated using existing beam data for fields with asymmetric collimator settings and under conditions of lateral disequilibrium.
Optimization of megavoltage beam and detector characteristics for portal imaging in radiotherapy
Authors: Flampouri Stella
Published: November 2003

Radiotherapy is usually verified with portal imaging using the treatment beam. These megavoltage x‐ray images suffer from poor contrast and can be improved by developing an imaging mode in the linear accelerator. The bremsstrahlung target is modified to produce enough low‐energy photons for imaging. In this work the problem of optimizing the beam/detector combination to achieve optimal image quality is addressed. To optimize the system, consisting of the linac and the detector for a given phantom or patient, Monte Carlo (MC) simulations and experimental measurements were carried out to investigate the parameters involved. A simple model of the system was generated for investigation of the effect of the target parameters on the quality of the image. The best targets were installed in a medical accelerator. To investigate the detector parameters in order to build the most suitable detector for imaging, the linac/phantom/detector system was simulated with MC. Contrast calculated from images predicted from the models gave a measure of the suitability of these detectors for imaging with the new beams. Experiments were carried out to verify the MC results. The optimized “imaging” beam was commissioned for clinical use and tested in a clinical trial to compare the new portal images with conventional ones. Camera based electronic portal imaging was also tested with the “imaging” beam and used for megavoltage CT acquisition. The optimal system of target (Al, 6 mm) and detector screen for film imaging and for the camera based EPID) produced high quality images with less dose than conventional systems.
Quantum Cascade Surface-Emitting Photonic Crystal Laser
Authors: Colombelli Raffaele , Srinivasan Kartik , Troccoli Mariano , Painter Oskar , Gmachl Claire F. , Tennant Donald M. , Sergent A. Michael , Sivco Deborah L. , Cho Alfred Y. , Capasso Federico
Published: November 2003

We combine photonic and electronic band structure engineering to create a surface-emitting quantum cascade microcavity laser. A high-index contrast two-dimensional photonic crystal is used to form a micro-resonator that simultaneously provides feedback for laser action and diffracts light vertically from the surface of the semiconductor surface. A top metallic contact allows electrical current injection and provides vertical optical confinement through a bound surface plasmon wave. The miniaturization and tailorable emission properties of this design are potentially important for sensing applications, while electrical pumping can allow new studies of photonic crystal and surface plasmon structures in nonlinear and near-field optics.
TWO PHOTON PHOTOCONDUCTIVITY OF ZnS USING XeCl LASER
Authors: SINGH R. D. , AHLAWAT D. S. , GAUR ARUN
Published: November 2003

Log Q versus log I ph characteristics and laser enhanced mobility in the case of ZnS have been studied using a XeCl laser. The comparison of results in this case with multiphoton photoconductivity of other materials indicates two photon excitation from a lower valance band, wherefrom one-photon excitation is forbidden but two-photon excitation is allowed. Since the band-gap of ZnS is smaller than the photon energy of the XeCl laser, the result seems to be interesting.
EXCITONS IN A NARROW PARABOLIC QUANTUM WELL UNDER EXTERNAL FIELDS
Authors: NICULESCU ECATERINA C. , BURILEANU LILIANA
Published: November 2003

The effects of electric and magnetic fields on the ground (1S-like) and excited (2S-like) states of an exciton in a narrow GaAs/Al x Ga 1-x As parabolic quantum well are studied. The effective-mass approximation within a perturbation-variational scheme is adopted. We find that the hole-mass anisotropy and nonparabolicity of the conduction band significantly modify the electron properties in such structures in which the quantum confinement plays a fundamental role. The effect of the electric field on the spatial distribution of the electron and hole is also investigated. In the low field regime, the diamagnetic shift of the exciton energies is calculated.
MAGNETIC BEHAVIOR OF IRON IONS IN THE P2O5·CaO GLASS MATRIX
Authors: ARDELEAN I. , ANDRONACHE C. , PǍŞCUŢǍ P.
Published: November 2003

The temperature dependence of the magnetic susceptibility of x Fe 2 O 3·(100-x)-[ P 2 O 5· CaO ] glasses with 0<x≤50 mol % have been investigated. These data revealed that the valence states and the distribution of iron ions in the glass matrix depend on the Fe 2 O 3 content. For the glasses with x≤1 mol % only Fe 3+ ions are evidenced. In the case of the glasses with 3≤x≤35 mol % both Fe 3+ and Fe 2 ions co-exist in the P 2 O 5· CaO glass matrix, the Fe 2+ ion content is higher than that of the Fe 3+ ions for glasses with x≥10 mol %. For the glasses with x>35 mol %, the evaluated values of the μ eff indicate either the presence of Fe + ions or the coordination influence on the magnetic moment of iron ions, but the presence of small quantities of the antiferromagnetic or ferrimagnetic interactions between iron ions in studied temperature range cannot be excluded. The high temperature susceptibility results indicate that the iron ions are isolated or participate in dipole-dipole interactions for glasses with x≤35 mol % and are antiferromagnetically coupled for higher contents of Fe 2 O 3.
HYBRIDIZATION EFFECTS IN SOME UTSi (2:1:3; 1:1:1; 2:3:1) COMPOUNDS
Authors: LUPSA ILEANA , VALEANU MIHAELA
Published: November 2003

The presence of magnetic moments in uranium atoms in some of U 2 TSi 3, UTSi and U 2 T 3 Si ( T is a 3d, 4d or 5d transition element) compounds is discussed in terms of the hybridization of s, p, d and f atomic orbitals. The hybridization strength in these ternary series of isostructural compounds was calculated using the semiquantitative band structure approach of Straub and Harrison. The prediction criterion for the presence of magnetic ordering, comparing the band width with a critical energy, seems to hold. The dominant influence of fd hybridization effects in the change of magnetic properties inside an isostructural group is in evidence.
NEW FOUR-MODE CHARGE-RELATED ENTANGLED STATE REPRESENTATION
Authors: FAN HONGYI , JING OUYANG
Published: November 2003

We construct a new kind of four-mode charge-related entangled state |q,k;n,m>θϕ in Fock space, which can describe the process of photons, emitted from two energy levels in a optical cavity, being absorbed by another two levels simultanuously. The relation between |q,k;n,m>θϕ and the four-mode entangled state |η,σ,τ>θϕ (H.-Y. Fan et al., Mod. Phys. Lett.B16, 861 (2002)) is pointed out.
EFFECT OF DISC-WATER INTERACTION ON THE WETTING BEHAVIOR OF WATER PHASE BETWEEN TWO DISCS
Authors: YUAN YIN-QUAN , ZOU XIAN-WU , XIONG PING-FAN , JIN ZHUN-ZHI
Published: November 2003

The effect of the interaction between a disc and water-like particle on the wetting behavior of water-like phase between two discs has been investigated by free energy analysis and discontinuous molecular dynamic simulations. A detailed description for the partial wetting-complete wetting transition is provided and the analytical expressions describing the wetting behavior are obtained.
Decoding Transcriptional Programs Regulated by PPARs and LXRs in the Macrophage
Authors: Ricote Mercedes , Valledor Annabel F. , Glass Christopher K.
Published: November 2003

Macrophages play essential roles in immunity and homeostasis. As professional scavengers, macrophages phagocytose microbes and apoptotic and necrotic cells and take up modified lipoprotein particles. These functions require tightly regulated mechanisms for the processing and disposal of cellular lipids. Under pathological conditions, arterial wall macrophages become foam cells by accumulating large amounts of cholesterol, contributing to the development of atherosclerosis. Peroxisome proliferator–activated receptors (PPARs) and liver X receptors (LXRs) are members of the nuclear receptor superfamily of transcription factors that have emerged as key regulators of macrophage homeostasis. PPARs and LXRs control transcriptional programs involved in processes of lipid uptake and efflux, lipogenesis, and lipoprotein metabolism. In addition, PPARs and LXRs negatively regulate transcriptional programs involved in the development of inflammatory responses. This review summarizes recent efforts to decode the differential and overlapping roles of PPARs and LXRs in the context of macrophage lipid homeostasis and the control of inflammation.
Cyclooxygenase-2 Expression and Inhibition in Atherothrombosis
Authors: Cipollone Francesco , Rocca Bianca , Patrono Carlo
Published: November 2003

Arachidonic acid metabolism plays an important role in acute ischemic syndromes affecting the coronary or cerebrovascular territory, as reflected by biochemical measurements of eicosanoid biosynthesis and the results of inhibitor trials in these settings. Two cyclooxygenase (COX)-isozymes have been characterized, COX-1 and COX-2, that differ in terms of regulatory mechanisms of expression, tissue distribution, substrate specificity, preferential coupling to upstream and downstream enzymes, and susceptibility to inhibition by the extremely heterogeneous class of COX-inhibitors. Although the role of platelet COX-1 in acute coronary syndromes and ischemic stroke is firmly established through ≈20 years of thromboxane metabolite measurements and aspirin trials, the role of COX-2 expression and inhibition in atherothrombosis is substantially uncertain, because the enzyme was first characterized in 1991 and selective COX-2 inhibitors became commercially available only in 1998. In this review, we discuss the pattern of expression of COX-2 in the cellular players of atherothrombosis, its role as a determinant of plaque “vulnerability,” and the clinical consequences of COX-2 inhibition. Recent studies from our group suggest that variable expression of upstream and downstream enzymes in the prostanoid biosynthetic cascade may represent important determinants of the functional consequences of COX-2 expression and inhibition in different clinical settings.
Nicotine Enhances Angiotensin II-Induced Mitogenic Response in Vascular Smooth Muscle Cells and Fibroblasts
Authors: Li Jian-Mei , Cui Tai-Xing , Shiuchi Tetsuya , Liu Hong-Wei , Min Li-Juan , Okumura Midori , Jinno Toyohisa , Wu Lan , Iwai Masaru , Horiuchi Masatsugu
Published: November 2003

Objective—

The pathogenetic mechanism of tobacco-related cardiovascular diseases is still not well defined. We examined the potential possibility of an interaction between nicotine, a major component of cigarette smoke, and angiotensin II (Ang II), which plays an important role in the pathogenesis of cardiovascular diseases characterized by Ang II type 1 (AT
1
) receptor-mediated abnormal growth of vascular smooth muscle cells (VSMC) and fibroblasts.

Methods and Results—

Nicotine or Ang II-stimulated [
3
H]thymidine incorporation and
c-fos
expression in adult rat aortic VSMC and adventitial fibroblast. The nicotine-induced DNA synthesis was not affected by valsartan, an AT
1
receptor-specific blocker, or PD123319, an Ang II type 2 (AT
2
) receptor-specific antagonist. Nicotine or Ang II stimulation rapidly increased extracellular signal-regulated kinase (ERK) activation, tyrosine- and serine-phosphorylation of signal transducer and activator of transcription (STAT)1 and STAT3, and p38 mitogen-activated protein kinase (p38 MAPK), in both cell types. Interestingly, co-administration of nicotine and Ang II at lower doses, which did not affect cell growth, induced DNA synthesis and
c-fos
expression accompanied by enhancement of ERK, STAT, and p38MAPK activity. PD98059, a mitogen-activated protein kinase/ERK kinase inhibitor, or SB23058, a p38MAPK inhibitor, significantly attenuated the vasotrophic effect of nicotine and Ang II.

Conclusions—

These results suggest that nicotine exerts a growth-promoting effect on vascular cells and enhances the Ang II-induced vasotrophic effect, which is at least partly mediated by the activation of ERK, STAT, and p38MAPK.
Evidence for Protein Kinase C-Mediated Activation of Rho- Kinase in a Porcine Model of Coronary Artery Spasm
Authors: Kandabashi Tadashi , Shimokawa Hiroaki , Miyata Kenji , Kunihiro Ikuko , Eto Yasuhiro , Morishige Kunio , Matsumoto Yasuharu , Obara Kazuo , Nakayama Koichi , Takahashi Shosuke , Takeshita Akira
Published: November 2003

Objective—

We have recently demonstrated that protein kinase C (PKC) and Rho-kinase play important roles in coronary vasospasm in a porcine model. However, it remains to be examined whether there is an interaction between the two molecules to cause the spasm.

Methods and Results—

A segment of left porcine coronary artery was chronically treated with IL-1β–bound microbeads in vivo. Two weeks after the operation, phorbol ester caused coronary spasm in vivo and coronary hypercontractions in vitro at the IL-1β–treated segment; both were significantly inhibited by hydroxyfasudil, a specific Rho-kinase inhibitor. Guanosine 5′-[γ-thio]triphosphate (GTPγS), which activates Rho with a resultant activation of Rho-kinase, enhanced Ca
2+
sensitization of permeabilized vascular smooth muscle cells, which were resistant to the blockade of PKC by calphostin C. The GTPγS-induced Ca
2+
sensitization was greater in the spastic segment than in the control segment. Western blot analysis revealed that only PKCδ isoform was activated during the hypercontraction.

Conclusions—

These results demonstrate that PKC and Rho-kinase coexist on the same intracellular signaling pathway, with PKC located upstream on Rho-kinase, and that among the PKC isoforms, only PKCδ may be involved. Thus, the strategy to inhibit Rho-kinase rather than PKC may be a more specific and useful treatment for coronary spasm.
The Role of β-Transducin Repeat-Containing Protein (β-TrCP) in the Regulation of NF-κB in Vascular Smooth Muscle Cells
Authors: Wang Xiaohong , Adhikari Neeta , Li Qinglu , Guan Zhanjun , Hall Jennifer L.
Published: November 2003

Objective—

Degradation of IκB is an essential step in nuclear factor (NF)-κB activation. However, the determinants regulating this process have not been defined in vascular smooth muscle cells (VSMCs). We hypothesized that the E3-ligase, β-transducin repeat-containing protein 1 (β-TrCP1), was a rate-determining mediator that regulates the ubiquitin-mediated degradation of IκBα (in VSMC).

Methods and Results—

Upregulation of β-TrCP1 accelerated the rate of IκBα degradation, leading to increased NF-κB activity. In contrast, VSMCs harboring a dominant-negative β-TrCP1 transgene lacking the F-box domain exhibited a reduction in serum-stimulated NF-kB activity but no alteration in response to tumor necrosis factor (TNF). These findings suggest that β-TrCP1 increases the rate of NF-κB activation but is not rate-limiting in response to TNF in VSMCs. Endogenous β-TrCP1 expression was regulated through the conserved Wnt cascade. Upregulation of Wnt1 resulted in β-catenin–mediated activation of Tcf-4, leading to increased β-TrCP1 expression and NF-κB activity. Furthermore, VSMCs harboring a Tcf-4 mutant lacking a β-catenin binding domain exhibited a significant reduction in β-TrCP1 expression along with abolishment of NF-κB activity.

Conclusions—

We provide the first evidence of crosstalk between the Wnt cascade and NF-κB signaling in VSMCs. This crosstalk is mediated through the E3-ligase, β-TrCP1.