bluuebunny/crossref_metadata_2025 huggingface dataset:
Adaptive robust stabilization of dynamic nonholonomic chained systems
Authors: Ge S. S. , Wang J. , Lee T. H. , Zhou G. Y.
Published: October 2004

In this article, the stabilization problem is investigated for dynamic nonholonomic systems with unknown inertia parameters and disturbances. First, to facilitate control system design, the nonholonomic kinematic subsystem is transformed into a skew‐symmetric form and the properties of the overall systems are discussed. Then, a robust adaptive controller is presented in which adaptive control techniques are used to compensate for the parametric uncertainties and sliding mode control is used to suppress the bounded disturbances. The controller guarantees the outputs of the dynamic subsystem (the inputs to the kinematic subsystem) to track some bounded auxiliary signals which subsequently drive the kinematic subsystem to the origin. In addition, it can also be shown all the signals in the closed loop are bounded. Simulation studies on the control of a unicycle wheeled mobile robot are used to show the effectiveness of the proposed scheme. © 2001 John Wiley & Sons, Inc.
Virtual passive control of flexible arms with collocated and noncollocated feedback
Authors: Wu Shang‐Teh
Published: October 2004

A novel approach to the control of flexible manipulators is proposed. The controller includes both joint‐variable and tip‐deflection feedback. It is shown that tip‐deflection feedback transforms the original structure into new system in which the structure parameters are virtually scaled up or down. The new system can hence be easily stabilized via a strictly passive feedback law. A co‐hub, lumped‐parameter structure with multiple massless links is first investigated and stability conditions are developed. The results are then applied to a distributed‐parameter flexible arm, which is decomposed into an equivalent lumped‐parameter structure via a set of modal functions normalized in a particular way. Tip‐deflection feedback is shown to be capable of enhancing control performance on a flexible arm, and stability is ensured as long as the gain associated with the noncollocated feedback satisfies a simple inequality. The stability criteria re valid independent of high‐order flexible modes. © 2001 John Wiley & Sons, Inc.
Dynamic modeling, stability, and energy efficiency of a quadrupedal walking machine
Authors: Lin Ben Sheng , Song Shin‐Min
Published: October 2004

In the past, the dynamics of walking machines was studied based on very simple or simplified leg structures. A more complete dynamic model is essential for the further development of a practical walking machine. In this paper, the dynamic model of a realistic quadrupedal walking machine is derived for simulation and real‐time control purposes. The walker has four cylindrical pantograph legs, and the whole system consists of twenty‐nine links. The walking gait is wave gait with at least three feet on the ground at any time. Significant efforts have been made to improve the computational efficiency of the inverse dynamics, and the required CPU time is less than 10 ms on an IBM 3090. The derived dynamic model is then applied to study two practical issues of walking: dynamic stability and mechanical efficiency of different legs and gaits. Simulation results show clear advantages of one leg type over another, and of some walking strategies in terms of adjusting velocities, strokes, and duty factors for greater efficiency. © 2001 John Wiley & Sons, Inc.
Fibonacci solitaire
Authors: Gnedin Alexander , Kerov Sergei
Published: October 2004

Fibonacci Solitaire is a combinatorial algorithm which associates with a permutation of [n]={1,…,n} a partition of [n] into couples and singletons. We study the output configuration when the algorithm is applied to a random permutation, with emphasis on the large n‐asymptotics. We show that the set of singletons, properly scaled, resembles a familiar ‘stick‐breaking’ Poisson configuration, whereas the configuration of couples becomes close to uniform. © 2002 John Wiley & Sons, Inc. Random Struct. Alg., 20, 71–88, 2002
Two‐coloring random hypergraphs
Authors: Achlioptas Dimitris , Han kim Jeong , Krivelevich Michael , Tetali Prasad
Published: October 2004

A 2‐coloring of a hypergraph is a mapping from its vertex set to a set of two colors such that no edge is monochromatic. Let H=H(k, n, p) be a random k‐uniform hypergraph on a vertex set V of cardinality n, where each k‐subset of V is an edge of H with probability p, independently of all other k‐subsets. Let \documentclass{article}\pagestyle{empty}\begin{document}$ m = p{{n}\choose{k}}$\end{document} denote the expected number of edges in H. Let us say that a sequence of events ℰn holds with high probability (w.h.p.) if limn→∞Pr[ℰn]=1. It is easy to show that if m=c2kn then w.h.p H is not 2‐colorable for c>ln 2/2. We prove that there exists a constant c>0 such that if m=(c2k/k)n, then w.h.p H is 2‐colorable. © 2002 Wiley Periodicals, Inc. Random Struct. Alg. 20: 249–259, 2002
Right order spectral gap estimates for generating sets of ℤ4
Authors: Löwe Matthias , Meise Christian
Published: October 2004

Using coupling arguments, a distance method and Zeifman's method we give sharp estimates on the spectral gap for a special case of the class of Markov chains on generating n‐tuples of Abelian groups. In our case the group is ℤ4. © 2002 Wiley Periodicals, Inc. Random Struct. Alg. 20: 220–238, 2002
Evasive random walks and the clairvoyant demon
Authors: Abrams Aaron , Landau Henry , Landau Zeph , Pommersheim James , Zaslow Eric
Published: October 2004

A pair of random walks (R, S) on the vertices of a graph G is successful if two tokens moving one at a time can be scheduled (moving only one token at a time) to travel along R and S without colliding. We consider questions related to P. Winkler's clairvoyant demon problem, which asks whether for random walks R and S on G, Pr[(R, S)is successful] >0. We introduce the notion of an evasive walk on G: a walk S so that for a random walk R on G, Pr[(R, S)is successful] >0. We characterize graphs G having evasive walks, giving explicit constructions on such G. Also, we show that on a cycle, the tokens must collide quickly with high probability. © 2002 Wiley Periodicals, Inc. Random Struct. Alg. 20: 220–229, 2002
The group‐noted state transition method applied to a PC management system
Authors: Hiyama Kunio
Published: October 2004

To improve software productivity, my colleagues and I pointed out in a previous paper that the state transition method is suitable as the functional description and implementation method. In that paper we proposed the distributed state transition method, which was derived from the model of distributed sequential machines and showed results obtained by applying it to an electronic switching system. In this paper, to enlarge the application range of the state transition method, I consider applying it to a PC management database system, and propose a new integrated design method derived from the single sequential machine model as being suitable. First I propose the “group‐noted state transition method” by introducing the sequential machine model. Then I propose this design method as follows. Initially, the function of the outer world of the system is classified into several groups, and management jobs are then divided into the same number of groups corresponding to them. The database information can also be classified in the same way and can support the design of the database system. After that, the state transition description is defined from the input/output information to/from the groups of the outer world. Furthermore, the method of notation in which the status group is added to the status name is proposed by classifying statuses using the concept of the management cycle. I also propose a new method for designing the software structure in which state transition diagram information is stored in the database system by converting it to table format. Results clarify that it is possible to make an integrated management database system by using this state transition method. They also clarify how to make a more advanced system by cooperating with the workflow system. © 2001 Scripta Technica, Syst Comp Jpn, 32(10): 13–21, 2001
High‐speed line detection method using hough transform in local area
Authors: Murakami Kazuhito , Naruse Tadashi
Published: October 2004

In this paper, a high‐speed line detection method using Hough transform is proposed. This approach is inspired by features of human foveal vision. In particular, line segment candidates are extracted at sufficient level of accuracy by applying Hough transform inside a local window. After that, greater areas are generated by extension of line segment candidates, and segment verification is executed. Such local window is then moved sequentially until the entire image is covered. Such processing makes possible absorption of quantization errors of Hough transform as well as extraction of shorter segments that were hard to detect by means of standard Hough transform. Generally, the proposed algorithm supports the same level of accuracy as standard Hough transform while featuring acceleration (and computing cost reduction); moreover, further performance boost can be achieved through parallel processing. © 2001 Scripta Technica, Syst Comp Jpn, 32(10): 22–30, 2001
Learning of Short Boolean Conjunctions from Negative Examples
Authors: Tsukiji Tatsuie , Tokutani Takashi
Published: October 2004

Learning from examples in the presence of overwhelmingly many irrelevant variables has been studied in the field of machine learning theory, where the learner is required to derive as succinct hypotheses as possible. In this paper, we consider the following computational learning problem: Given a set of negative examples in n Boolean variables, the learner is required to find O(log n) relevant variables whose conjunction gives a consistent hypothesis. This problem belongs to a complexity class called β2. We prove that this problem is equivalent, by probabilistic log‐space Turing reduction, to the problem of finding satisfiable assignments for polynomial‐size ${\bf \Pi}^{0}_{3}$‐circuits with O(log2 n) inputs. As a consequence, we can show that learning of O(log n)‐length Boolean conjunctions from negative examples is neither β2‐hard unless P ⊆ POLYLOG‐SPACE, nor polynomial‐time computable unless NP ⊆ DTIME(2O(√n)).

In this paper, we also discuss the polynomial‐time learnability of an O(log n)‐length monotone Boolean conjunction from negative examples, when the examples are drawn from the uniform distribution. © 2001 Scripta Technica, Syst Comp Jpn, 33(1): 1–7, 2002
A Method of Embedding Binary Data into JPEG Bitstreams
Authors: Kobayashi Hiroyuki , Noguchi Yoshihiro , Kiya Hitoshi
Published: October 2004

This paper considers irreversible coding by JPEG, and proposes a method of embedding binary data into the image. The proposed method embeds the information into the AC coefficients after quantization. The information is embedded in the AC coefficients of higher frequency, and by setting the quantization table corresponding to these AC coefficients to small values, visual image degradation is limited. In the proposed method, the embedded information is completely recovered in decoding, leaving little effect on the image after recovering the information. The coded sequence can be decoded using a conventional JPEG decoder, even in an environment where the information is not to be recovered or cannot be recovered. The method is designed so that image degradation is also limited in such a case. © 2001 Scripta Technica, Syst Comp Jpn, 33(1): 18–26, 2002
Susceptibility to DNA damage induced by antibiotics in lymphocytes from malnourished children
Authors: González C. , Nájera O. , Cortés E. , Toledo G. , López L. , Betancourt M. , Ortiz R.
Published: October 2004

Infectious disease and malnutrition in children are public health problems in developing countries. Malnutrition is associated with higher levels of DNA damage, and this increased damage could be due to different factors, including the possibility that cells from malnourished children could be more susceptible to environmental damage. The aim of the present study was to evaluate the susceptibility of lymphocytes from malnourished children to DNA damage induced by antibiotics by using the comet assay. The same group of malnourished infected children were studied before and after a treatment period, and compared to a group of well‐nourished infected children. Results showed that before and after drug treatment, tail length migration was two times greater in malnourished than in well‐nourished children. The proportion of cells with high damage was also increased in malnourished children. Additionally in well‐nourished and malnourished children, a cell subpopulation (non‐damaged cells) more resistant to DNA damage induced by antibiotics was observed; this was more prevalent in the well‐nourished children. Meanwhile, in malnourished children, a cell population seems to be more susceptible and reaches higher levels of DNA damage. This might help explain the impaired immune response observed in malnourished children. The increased DNA migration and the increased proportion of cells with higher levels of damage seem to indicate that malnourished children are more susceptible to DNA damage induced by drugs. Teratogenesis Carcinog. Mutagen. 22:147–158, 2002. © 2002 Wiley‐Liss, Inc.
The influence of 2‐chlorodeoxyadenosine (2‐CdA) on the adenine energy charge and glutathione content of human erythrocytes
Authors: Marczak A. , Bukowska B. , Koczmara M. , Jóźwiak Z.
Published: October 2004

We have examined the effect of exposure of human erythrocytes to the new chemotherapy drug 2‐chlorodeoxyadenosine (2‐CdA, cladribine), focusing on the glutathione (GSH and GSSG) content and the adenine energy charge (AEC). Incubation of erythrocytes with 0.1–5 μg/ml 2‐CdA induced no significant change in the reduced or total glutathione level or in the AMP and ATP concentrations. The ADP concentration increased slightly and the AEC value is in the range typical of healthy organisms. Incubation of erythrocytes with 2‐CdA also caused cell shape changes, converting most of the cells to echinocytes.
Assessment of left atrial input impedance in normal subjects and in hypertensive patients
Authors: Dernellis John , Panaretou Maria
Published: October 2004

Background

To assess left atrial (LA) input impedance in patients with signs and/or symptoms of heart failure and normal left ventricular ejection fraction, transesophageal Doppler pulmonary venous (PV) flow velocity and pulmonary capillary wedge pressure (PCWP) were studied in 20 patients and compared to 20 matched normal controls.

Methods

LA impedance was calculated as the ratio of harmonic terms of the PCWP (measured by right heart catheterization) to the corresponding harmonic terms of PV flow (measured by transesophageal Doppler echocardiography). Eight harmonics were analyzed.

Results

Left ventricular mass index (LVMI, p<0.001), heart rate (p<0.05), systolic and diastolic blood pressure (p<0.001), isovolumic relaxation time (IVRT, p<0.001), peak A transmitral flow velocity (p<0.001), peak reversal atrial PV flow velocity (p<0.001) and LA diameter (p<0.001) were increased in patients compared to controls. Spectra of impedance moduli were displaced upwards and to the right. The increase in the impedance moduli was observed at all frequencies of the first to seventh harmonic components (p<0.001). In multivariate tests LVMI (p=0.003), IVRT (p=0.001), and LA diameter (p=0.007) had a significant effect on all harmonic components of the impedance moduli (adjusted R2=0.970 to 0.999, p<0.001).

Conclusions

LA input impedance derived from data obtained invasively and semi‐invasively represents left ventricular diastolic function. Resistance to left ventricular filling is increased in hypertensive patients.
Estimating and forecasting pre-fishery abundance of Atlantic salmon (Salmo salar L.) in the Northeast Atlantic for the management of mixed-stock fisheries
Authors: Potter E.C.E. , Crozier W.W. , Schön P-J. , Nicholson M.D. , Maxwell D.L. , Prévost E. , Erkinaro J. , Gudbergsson G. , Karlsson L. , Hansen L.P. , MacLean J.C. , Ó Maoiléidigh N. , Prusov S.
Published: October 2004

Most exploitation of Atlantic salmon (Salmo salar) is restricted to “homewater fisheries”, which operate close to or within the rivers of origin of the stocks, but two “distant-water fisheries” are permitted to operate off the west coast of Greenland and in the Norwegian Sea, and take salmon from a large number of rivers over a wide geographical area. Providing robust quantitative catch advice for these mixed-stock fisheries depends upon the ability to forecast stock abundance for about 2000 salmon river-stocks around the North Atlantic, more than 1500 of which are in Europe. A “run-reconstruction” model is presented for estimating the historic pre-fishery abundance (PFA) of salmon for countries or regions around the Northeast Atlantic, based upon catch data and estimates of non-reporting rates and exploitation rates. These estimates are then used to develop predictive models of PFA on the basis of estimates of the egg deposition, derived from the run-reconstruction model and various environmental data. Although the selected environmental indices correlated with the PFA of both southern and northern European stock complexes, the main statistical significance in the forecast models was provided by temporal trends in the PFA. Clearly, such a model is only tenable in the short term, and will be poor at predicting a major change in stock status. Alternative approaches, based upon juvenile production indices and including Bayesian techniques, are therefore being considered.
Ultraviolet‐ and short‐wavelength cone contributions alter the early components of the ERG of young zebrafish
Authors: Bilotta Joseph , Trace Sara E. , Vukmanic Eric V. , Risner Michael L.
Published: October 2004

The electroretinogram (ERG) is a commonly used measure to examine retinal processing in both basic and clinical research. The purpose of this study was to determine the retinal mechanisms responsible for the developmental differences found in the zebrafish ERG waveform. The ERG of young zebrafish possesses a voltage‐negative response to ultraviolet‐ and short‐wavelength stimuli, but not to middle‐ and long‐wavelength stimuli; the ERG of adult zebrafish does not possess this response component. ERGs were obtained from young zebrafish before and after the introduction of either aspartate, or a combination of APB (dl‐2‐amino‐4‐phosphonobutyric acid) and PDA (cis‐2,3‐piperidinedicarboxylic acid) in order to suppress the responses of various types of retinal neurons. Log irradiance versus response amplitude functions of the ERG response to 200‐ms stimuli of various wavelengths at various times following stimulus onset (70 and 120 ms) was derived as well as spectral sensitivity. Aspartate eliminated all voltage‐positive responses regardless of stimulus wavelength; irradiance–response functions following aspartate were similar to the early responses of young control fish to ultraviolet‐ and short‐wavelength stimuli. APB + PDA produced similar but not identical results as aspartate, suggesting that the combination of these agents does not completely eliminate all post‐receptoral contributions to the ERG. Spectral sensitivity functions derived from aspartate‐exposed subjects at various time measurements were dominated by contributions from ultraviolet‐ and short‐wavelength‐sensitive cone types. These wavelength‐dependent ERG responses are similar to those found in humans with enhanced S‐cone syndrome. Finally, ERG waveform differences across stimulus wavelength suggest that the circuitry of ultraviolet‐ and short‐wavelength cone types is different to that of middle‐ and long‐wavelength cone types in young zebrafish.
Beurteilung der Fahreignung
Authors: Golz D. , Huchler S. , Jörg A. , Küst J.
Published: October 2004

Zusammenfassung: In diesem Artikel wird zunächst erörtert, welche Hinweise und Vorgaben zur Beurteilung der Fahreignung bei neurologisch erkrankten Kraftfahrern der Fahrerlaubnis-Verordnung ( FeV, 1998 ), den Begutachtungs-Leitlinien zur Kraftfahrereignung ( Bundesanstalt für Straßenwesen, 2000 ) sowie dem Kommentar zu den Begutachtungs-Leitlinien ( Schubert et al., 2002 ) zu entnehmen sind. Diese Inhalte werden kritisch diskutiert. Nachfolgend wird beschrieben, welche Vorgehensweise bei der Untersuchung der Fahreignung zu empfehlen ist. Im einzelnen wird dabei auf die Diagnostik von Leistungen im Bereich der visuellen Wahrnehmung, der Aufmerksamkeit, der exekutiven und intellektuellen Funktionen, der motorischen Funktionen sowie von Persönlichkeitsfaktoren eingegangen. Ferner werden die Durchführung einer Fahrverhaltensprobe sowie Exploration und Verhaltensbeobachtung zur Urteilsbildung näher beschrieben.
Analysis of Self-Concept in Older Adults in Different Contexts
Authors: de Gracia Blanco Manuel , Garre Olmo Josep , Arbonès María Marcó , Monreal Bosch Pilar
Published: October 2004

Summary: Self-concept is a construct consisting of a group of specific self-perceptions that are hierarchically organized. Age-associated changes of self-concept are related to the individual's perception of the changes occurring throughout the aging process. The authors examined external validity and internal consistency of an instrument that has been developed to assess self-concept in older adults and examined self-concept's characteristics in two different contexts. Results confirm the multidimensionality of the scale and show a satisfactory external validity, indicating good discriminatory capacity. Findings support the hypothesis that older people who live in a nursing home have a poor self-esteem, self-concept, and psychological well-being and have a greater presence of depressive symptoms than people who live in their own home.
The Role of Structure in the Assessment of Psychopathology
Authors: Leichsenring Falk
Published: October 2004

Summary: This study investigated the role that the structure of a diagnostic instrument plays in the assessment of personality functioning. Empirical studies have shown that the cards of the Rorschach and Holtzman Inkblot Technique (HIT) vary significantly with regard to their structure. Thus, it was possible to investigate if cards of high vs. low structure tend to elicit specific diagnostically useful responses. For this purpose, samples of normals (n = 30), patients with neurotic disorders (n = 30), borderline patients (n = 30), acute schizophrenics (n = 25), and chronic schizophrenics (n = 25) were studied with the HIT. For each diagnostic group it was examined if cards of high vs. low structure tended to elicit more thought disordered responses, hostility, and anxiety according to the HIT scoring system. With regard to structure, two aspects were differentiated, structural vs. interpretative ambiguity of the HIT cards. In all nonschizophrenic groups, cards of high structural ambiguity elicited significantly less thought disordered responses. By contrast, cards of high interpretative ambiguity elicited more thought disordered responses, anxiety, and hostility in all groups except the chronic schizophrenics. The measures of structural vs. interpretative ambiguity of the HIT cards showed a negative correlation in all diagnostic groups. According to these results, both aspects of ambiguity and their interplay play an important role in the assessment of psychopathology, at least within the range of ambiguity represented by the inkblots of the HIT.
Some Psychometric Properties of the Ghent Parental Behavior Scale1
Authors: Van Leeuwen Karla G. , Vermulst Ad A.
Published: October 2004

Summary: The theoretical basis of the Ghent Parental Behavior Questionnaire (GPBS) originates from social-learning theories. Parents rate the frequency of their behavior toward a target child between 8 and 14 years old, and children rate the behavior of their parents. Confirmatory factor analyses provide evidence for a solid factor structure in different samples. Nine scales are distinguished: Positive parenting, Monitoring, Rules, Discipline, Inconsistent discipline, Harsh punishment, Ignoring, Material rewarding, and Autonomy. It is also feasible to distinguish two second-order factors: Support and Negative control. The internal consistency is acceptable to good. Correlations between ratings of parents and children are positive and significant. We also find evidence for the assumption that positive parenting is negatively associated with problem behavior and stress in parenting, and, in addition, that inadequate parenting is positively related to problem behavior and stress in parenting.
Magnetotail behavior during storm time “sawtooth injections”
Authors: Lui A. T. Y. , Hori T. , Ohtani S. , Zhang Y. , Zhou X. Y. , Henderson M. G. , Mukai T. , Hayakawa H. , Mende S. B.
Published: October 2004

A series of magnetic storms occurred during 16–21 April 2002 with multiple local minima in the Dst index. During this storm period, Geotail traversed the magnetotail from the premidnight tail lobe in the midtail region to the postmidnight plasma sheet in the near‐Earth region. Simultaneous observations of energetic particles at the geostationary altitude showed the feature known as “sawtooth injections” remarkably well from 18 April to 19 April. This conjunction allows us to examine the magnetotail behavior in the tail lobe and the plasma sheet associated with sawtooth injections. In the tail lobe, close but not perfect time coincidence is found between injection onset and start of southward dipping of the magnetic field vector in the tail lobe. Long‐duration (1–2 hours) southward dipping in the tail lobe magnetic field appears to be a global behavior of the tail lobe in association with sawtooth injections. In the plasma sheet, intermittent occurrences of plasma flow reversal from sunward to tailward and of magnetic field from northward to southward are found. The duration of southward magnetic field is typically short (1–5 min) within the plasma sheet. There are some sawtooth injections that are not accompanied by any significant changes in plasma sheet parameters (plasma flows, magnetic and electric fluctuation levels), suggesting the plasma sheet behavior to be localized even in association with sawtooth injections that are global in nature. There was no indication of the magnetotail being driven in a relatively “steady state” in association with sawtooth injections during this sequence of storms.
Oxygen atom Rydberg emission in the equatorial ionosphere from radiative recombination
Authors: Slanger T. G. , Cosby P. C. , Huestis D. L. , Meier R. R.
Published: October 2004

Radiative recombination of O+ generates a variety of O‐atom Rydberg levels, which then radiatively cascade to the ground state. The last two steps in the cascade produce 844.6 nm and 130.2–130.6 nm radiation in the triplet set of Rydberg levels and 777.2–777.5 nm and 135.6 nm radiation in the quintets. These four emissions are well known from ionospheric observations, and the higher members of the cascades are sometimes seen in auroral spectra but rarely in the nightglow. Sky spectra taken in 2000 at the Keck II telescope with the ESI echelle spectrograph reveal 20 members of the Rydberg transitions in the 390–930 nm region not previously observed in the nightglow. Most of these are not seen in earlier Keck spectra, taken at solar minimum. We are able to quantify the relative intensities of the emissions across the entire wavelength region using standard star spectra, allowing comparisons to be made with theoretical calculations. As the atmosphere is optically thin for the quintet transitions, corrections for radiative scattering are not necessary, and relative agreement between theory and observations is excellent. For the triplets the data agree more closely with the optically thick calculations. The relationship between the intensities of the quintet 3d‐3p (926–926.6 nm) and the triplet 3p‐3s (844.6 nm) multiplets is investigated and found to be linear. Accurate wavelengths are determined for the Rydberg quintets on the basis of observations with the high‐resolution (∼40,000) Keck I/HIRES system. For the triplets the multiplets are incompletely resolved. Examples of spectra are presented where the 844.6 nm multiplet is the only OI Rydberg emission observed. We argue that the cause is Bowen fluorescence, a consequence of photoexcitation of the OI 3d‐2p transition by H Lyman‐β radiation in the geocorona. The fact that so many of the oxygen Rydberg lines have been identified in this study and that their intensities are consistent with cascade models of radiative recombination is a strong confirmation of the importance of this process in the tropical nightglow near solar maximum.
Long‐term and seasonal trends in stratification in the California Current, 1950–1993
Authors: Palacios Daniel M. , Bograd Steven J. , Mendelssohn Roy , Schwing Franklin B.
Published: October 2004

State‐space model decomposition of subsurface temperatures from the World Ocean Database is used to detect and characterize changes in thermal stratification in the upper 200 m of the California Current System (CCS) over the period 1950–1993. Model results are analyzed at eight locations representing the meridional and offshore extent of the CCS between 31°N and 40°N. Thermocline strength, depth, and temperature are derived from the mean‐level trend term and the seasonal component of the state‐space models. Over the 44 years, the mean level of the coastal thermocline strengthened and deepened, while it weakened and shoaled offshore. These tendencies are likely the result of geostrophic adjustment to changes in basin‐scale circulation, as well as to a long‐term increase in upper ocean heat content of 2–9% throughout the study area. Reduction in nutrient inputs to the surface layer resulting from these climate signals are a likely explanation for the pronounced decline in biological production in CCS ecosystems observed over the same period. Substantial decadal variability superimposed on these linear tendencies may play a role in determining the response of the upper ocean to interannual events such as El Niño. The seasonal component of thermocline depth and strength exhibited a high degree of nonstationarity, with alternating periods of weakened and enhanced annual cycles lasting 3–5 years, along with changes in the phase. This changing seasonality may have implications for marine species whose life cycles are closely tuned to the seasonal cycle.
Numerical study of tidal circulation and nonlinear dynamics in Lunenburg Bay, Nova Scotia
Authors: Sheng Jinyu , Wang Liang
Published: October 2004

A three‐dimensional ocean circulation model is used to study the barotropic tidal circulation and nonlinear tidal dynamics in Lunenburg Bay, Nova Scotia. The model performance is first assessed using the observed bottom pressures and currents made in Septembers of 1991 and 2003. The model results reproduce reasonably well the observed tidal circulation in the study region. The simulated tidal circulation is dominated by the semidiurnal (M2) tide and an intense jet‐like flow through a narrow channel connecting Lunenburg Bay and two shallow coves. To demonstrate the importance of nonlinear tidal dynamics in the region, the first two harmonics of M2 (i.e., M4 and M6) are computed from the model results forced by the M2 tide at the model open boundaries. Both M4 and M6 are relatively large in western Lunenburg Bay and vicinity, indicating the importance of the nonlinear tidal dynamics over these areas. To quantify the role of various nonlinear terms in generating the intense jet and associated residual flows in the region of the jet, both transient and tidally averaged (time mean) momentum equations are examined. The transient and time mean momentum balances demonstrate that the nonlinear interaction of the tidal currents with local bathymetry is balanced primarily by the horizontal pressure gradients, momentum advection, and dissipation. The Coriolis effect plays a minor role in the study region.
Using the “blue spike” to characterize biomass‐burning sites during Southern African Regional Science Initiative (SAFARI) 2000
Authors: McCourt M. L. , McMillan W. W. , Ackerman S. , Holz R. , Revercomb H. E. , Tobin D.
Published: October 2004

During several flights of the ER‐2 while participating in the Southern African Regional Science Initiative (SAFARI 2000), the University of Wisconsin–Madison's Scanning High Resolution Interferometer Sounder (S‐HIS) obtained spectra containing isolated fires within its field of view (FOV). These fire‐laden FOVs contain a spectral feature caused by rotational hot band transitions of CO2 near 2400 cm−1. Because of its location on the blue side of the 4.3 μm band of CO2, this feature is commonly referred to as the “blue spike.” Using this feature, we detected fires on four flights: 24 and 27 August and 6 and 7 September 2000. Fire locations are further verified by the ER‐2 pilot's flight logs and elevated brightness temperatures in the thermal detectors of the MODIS Airborne Simulator (MAS) also on board the ER‐2. Using line‐by‐line radiative transfer calculations (Genln2) with corrections for a fire's extreme high temperatures (HiTemp), we model S‐HIS spectra for various scenes: background (cool surface and cool atmosphere), smoldering (warm surface and cool atmosphere), hot gas layer (cool surface and warm atmosphere), and fire (hot surface and hot atmosphere) cases. Using the controlled burn in the Timbavati Game Reserve on 7 September 2000 as a test case, we spectrally modeled the blue spike feature seen in the spectra obtained by S‐HIS while the ER‐2 flew over the fire. For this case, we found that ∼4.12 ± 0.05% of the FOV contained the hot gas layer while ∼0.23 ± 0.05% was actively burning. Originally viewed as a straightforward task of using the blue spike to characterize the fire temperature and size (fraction of S‐HIS FOV), our analysis shows that numerous variables, including amount of carbon dioxide, amount of water vapor, and the temperature near the fire, play significant roles in the blue spike's shape and spectral position.
New radiation environment and effects models in the European Space Agency's Space Environment Information System (SPENVIS)
Authors: Heynderickx D. , Quaghebeur B. , Wera J. , Daly E. J. , Evans H. D. R.
Published: October 2004

The European Space Agency (ESA) Space Environment Information System (SPENVIS) provides standardized access to models of the hazardous space environment through a user‐friendly Web interface, available at http://www.spenvis.oma.be/. SPENVIS is designed to help spacecraft engineers perform rapid analyses of environmental problems and, with extensive documentation and tutorial information, allows engineers with relatively little familiarity with the models to produce reliable results. SPENVIS is based on internationally recognized standard models and methods in many domains. It uses an ESA‐developed orbit generator to produce orbital point files necessary for many different types of problem. It has various reporting and graphical utilities and extensive help facilities. SPENVIS also contains an active, integrated version of the European Cooperation for Space Standardization Space Environment Standard, and access to in‐flight data. Apart from radiation and plasma environments, SPENVIS includes meteoroid and debris models, atmospheric models (including atomic oxygen), and magnetic field models. Recently, the radiation sources and effects module have been rewritten, providing enhanced mission analysis features, new radiation effects models, and streamlined navigation between various model pages.
The 5‐HT4 receptor agonist, tegaserod, is a potent 5‐HT2B receptor antagonist in vitro and in vivo
Authors: Beattie D T , Smith J A M , Marquess D , Vickery R G , Armstrong S R , Pulido‐Rios T , McCullough J L , Sandlund C , Richardson C , Mai N , Humphrey P P A
Published: October 2004

Tegaserod (Zelnorm®) is a potent 5‐hydroxytryptamine4 (5‐HT4) receptor agonist with clinical efficacy in disorders associated with reduced gastrointestinal motility and transit. The present study investigated the interaction of tegaserod with 5‐HT2 receptors, and compared its potency in this respect to its 5‐HT4 receptor agonist activity.

Tegaserod had significant binding affinity for human recombinant 5‐HT2A, 5‐HT2B and 5‐HT2C receptors (pKi=7.5, 8.4 and 7.0, respectively). The 5‐HT2B receptor‐binding affinity of tegaserod was identical to that at human recombinant 5‐HT4(c) receptors (mean pKi=8.4) in human embryonic kidney‐293 (HEK‐293) cells stably transfected with the human 5‐HT4(c) receptor.

Tegaserod (0.1–3 μM) inhibited 5‐HT‐mediated contraction of the rat isolated stomach fundus potently (pA2=8.3), consistent with 5‐HT2B receptor antagonist activity. Tegaserod produced, with similar potency, an elevation of adenosine 3′,5′ cyclic monophosphate in HEK‐293 cells stably transfected with the human 5‐HT4(c) receptor (mean pEC50=8.6), as well as 5‐HT4 receptor‐mediated relaxation of the rat isolated oesophagus (mean pEC50=8.2) and contraction of the guinea‐pig isolated colon (mean pEC50=8.3).

Following subcutaneous administration, tegaserod (0.3 or 1 mg kg−1) inhibited contractions of the stomach fundus in anaesthetized rats in response to intravenous dosing of α‐methyl 5‐HT (0.03 mg kg−1) and BW 723C86 (0.3 mg kg−1), selective 5‐HT2B receptor agonists. At similar doses, tegaserod (1 and 3 mg kg−1 subcutaneously) evoked a 5‐HT4 receptor‐mediated increase in colonic transit in conscious guinea‐pigs.

The data from this study indicate that tegaserod antagonizes 5‐HT2B receptors at concentrations similar to those that activate 5‐HT4 receptors. It remains to be determined whether this 5‐HT2B receptor antagonist activity of tegaserod contributes to its clinical profile.

British Journal of Pharmacology (2004) 143, 549–560. doi:10.1038/sj.bjp.0705929
Evidence for P2Y1, P2Y2, P2Y6 and atypical UTP‐sensitive receptors coupled to rises in intracellular calcium in mouse cultured superior cervical ganglion neurons and glia
Authors: Calvert Jennifer A , Atterbury‐Thomas Amelia E , Leon Catherine , Forsythe Ian D , Gachet Christian , Evans Richard J
Published: October 2004

P2Y receptors are expressed in the nervous system and are involved in calcium signalling in neurons and glia. In the superior cervical ganglion (SCG), RT–PCR analysis indicated the presence of P2Y1,2&6 receptors. Rises in intracellular calcium in response to P2Y receptor stimulation were determined from adult mouse cultured SCG neurons and glia.

ADP evoked suramin (100 μM)‐ and pyridoxalphosphate‐6‐azophenyl‐2′,4′‐disulphonic acid (PPADS, 30 μM)‐sensitive rises in intracellular calcium in ∼80% of SCG neurons (EC50∼20 μM). ADP‐evoked responses were abolished in neurons from P2Y1 receptor‐deficient mice (responses to UTP were unaffected).

The pyrimidines UTP (EC50∼85 μM) and UDP (EC50>90 μM) evoked PPADS‐ and suramin‐sensitive responses in ∼70 and ∼20% of SCG neurons, respectively.

In SCG glial cells, ADP (EC50∼30 μM) evoked calcium responses in ∼50% of glia. These were suramin and PPADS sensitive and essentially abolished in SCG glial cells cultured from adult P2Y1 receptor‐deficient mice.

UTP (EC50∼25 μM) and UDP (EC50>200 μM) evoked suramin‐ and pyridoxalphosphate‐6‐azophenyl‐2′,5′‐disulphonate‐sensitive rises in calcium in ∼60 and 20% SCG glial cells, respectively.

These results indicate the presence of several P2Y receptors coupled to an increase in intracellular calcium in the SCG: ADP‐sensitive P2Y1 receptors and UDP‐sensitive P2Y6 receptors in SCG neurons and glial cells, a novel UTP‐sensitive P2Y receptor in SCG neurons and UTP‐ and ATP‐sensitive P2Y2 receptors in SCG glia.

British Journal of Pharmacology (2004) 143, 525–532. doi:10.1038/sj.bjp.0705959
Heterologous desensitization of the sphingosine‐1‐phosphate receptors by purinoceptor activation in renal mesangial cells
Authors: Xin Cuiyan , Ren Shuyu , Pfeilschifter Josef , Huwiler Andrea
Published: October 2004

Sphingosine‐1‐phosphate (S1P) is considered a potent mitogen for mesangial cells and activates the classical mitogen‐activated protein kinase (MAPK) cascade via S1P receptors. In this study, we show that S1P signalling is rapidly desensitized upon S1P receptor activation. A complete loss of S1P sensitivity occurs after 10 min of S1P pretreatment and remains for at least 8 h. A similar desensitization is also seen with the S1P mimetic FTY720‐phosphate, but not with the nonphosphorylated FTY720, nor with sphingosine or ceramide.

Prestimulating the cells with extracellular ATP or UTP, which bind to and activate P2Y receptors on mesangial cells, a similar rapid desensitization of the S1P receptor occurs, suggesting a heterologous desensitization of S1P receptors by P2Y receptor activation. Furthermore, adenosine binding to P1 receptors triggers a similar desensitization. In contrast, two other growth factors, PDGF‐BB and TGFβ2, have no significant effect on S1P‐induced MAPK activation.

S1P also triggers increased inositol trisphosphate (IP3) formation, which is completely abolished by S1P pretreatment but only partially by ATP pretreatment, suggesting that IP3 formation and MAPK activation stimulated by S1P involve different receptor subtypes.

Increasing intracellular cAMP levels by forskolin pretreatment has a similar effect on desensitization as adenosine. Moreover, a selective A3 adenosine receptor agonist, which couples to phospholipase C and increases IP3 formation, exerted a similar effect.

Pretreatment of cells with various protein kinase C (PKC) inhibitors prior to ATP prestimulation and subsequent S1P stimulation leads to a differential reversal of the ATP effect. Whereas the broad‐spectrum protein kinase inhibitor staurosporine potently reverses the effect, the PKC‐α inhibitor CGP41251, the PKC‐δ inhibitor rottlerin and calphostin C show only a partial reversal at maximal concentrations.

Suramin, which is reported as a selective S1P3 receptor antagonist compared to the other S1P receptor subtypes, has no effect on the S1P‐induced MAPK activation, thus excluding the involvement of S1P3 in this response.

In summary, these data document a rapid homologous and also heterologous desensitization of S1P signalling in mesangial cells, which is mechanistically triggered by PKC activation and eventually another staurosporine‐sensitive protein kinase, as well as by increased cAMP formation.

British Journal of Pharmacology (2004) 143, 581–589. doi:10.1038/sj.bjp.0705980
Macroscopic, microscopic and biochemical characterisation of spontaneous colitis in a transgenic mouse, deficient in the multiple drug resistance 1a gene
Authors: Banner Katharine H , Cattaneo Christophe , Net Jean‐Loic Le , Popovic Aleksandar , Collins David , Gale Jeremy D
Published: October 2004

A novel animal model of spontaneous colonic inflammation, the multiple drug‐resistant (mdr1) a−/− mouse, was identified by Panwala and colleagues in 1998. The aim of our study was to further characterise this model, specifically by measuring cytokines that have been implicated in inflammatory bowel disease (IBD) (IL‐8 and IFN‐γ) in the colon/rectum of mdr1a−/− mice, and by determining the sensitivity of these, together with the macroscopic, microscopic and disease signs of colitis, to dexamethasone (0.05, 0.3 and 2 mg kg−1 subcutaneously (s.c.) daily for 7 days).

All mdr1a−/− mice had microscopic evidence of inflammation in the caecum and colon/rectum, while control mice with the same genetic background did not. Significant increases in colon/rectum and caecal weights and also in cytokine levels (both IFN‐γ and IL‐8) in homogenised colon/rectum were observed in mdr1a−/− mice compared to mdr1a+/+ mice.

Dexamethasone reduced the increases in tissue weights and also microscopic grading of colitis severity, but had no effect on IFN‐γ or IL‐8.

This study supports the similarity of the gastrointestinal inflammation present in mdr1a−/− mice to that of human IBD, in particular Crohn's disease. This has been demonstrated at the macroscopic and microscopic levels, and was supported further by elevations in colonic levels of IFN‐γ and IL‐8 and the disease signs observed. The incidence of colitis was much higher than previously reported, with all mice having microscopic evidence of colitis. The limited variance between animals in the parameters measured suggests that this model is reproducible.

British Journal of Pharmacology (2004) 143, 590–598. doi:10.1038/sj.bjp.0705982
Chemical insights from structural studies of enzymes
Authors: Naismith J.H.
Published: October 2004

The rapid progress in structural and molecular biology over the past fifteen years has allowed chemists to access the structures of enzymes, of their complexes and of mutants. This wealth of structural information has led to a surge in the interest in enzymes as elegant chemical catalysts. Enzymology is a distinguished field and has been making vital contributions to medicine and basic science long before structural biology. This review for the Colworth Medal Lecture discusses work from the author's laboratory. This work has been carried out in collaboration with many other laboratories. The work has mapped out the chemical mechanisms and structures of interesting novel enzymes. The review tries to highlight the interesting chemical aspects of the mechanisms involved and how structural analysis has provided a detailed insight. The review focuses on carbohydrate-processing pathways in bacteria, and includes some recent data on an integral membrane protein.
Distribution of lipid raft markers in live cells
Authors: Glebov O.O. , Nichols B.J.
Published: October 2004

GPI (glycosylphosphatidylinositol)-anchored proteins are characteristic components of biochemically defined lipid rafts. Rafts may be involved in T-cell stimulation, but it is not clear whether molecules involved in TCR (T-cell receptor) signalling are partitioned to T-cell synapses through raft microdomains or through specific protein–protein interactions. We have used FRET (fluorescence resonance energy transfer) analysis to study the distribution of GPI-anchored fluorescent proteins in the plasma membrane of live cells. Multiple criteria suggested that FRET between different GPI-anchored fluorescent proteins in COS-7 or unstimulated Jurkat T-cells is generated by a random, unclustered distribution. Stimulation of TCR signalling in Jurkat T-cells by beads coated with antibodies against TCR subunits resulted in localized increases in fluorescence of raft markers. However, measurements of FRET and ratio imaging showed that there was no detectable clustering and no overall enrichment of raft markers in these regions.
Can membrane nanotubes facilitate communication between immune cells?
Authors: Önfelt B. , Davis D.M.
Published: October 2004

Recent observations have revealed that intercellular connections can be formed through membrane nanotubes. These delicate structures could facilitate transport of organelles and membrane proteins between cells. The sharing of cell surface and cytoplasmic components between cells could be commonplace in biology, but an important physiological role for membrane nanotubes between immune cells is difficult to test with current technology.