bluuebunny/crossref_metadata_2025 huggingface dataset:
Deriving historical equilibrium-line altitudes from a glacier length record by linear inverse modelling
Authors: Klok E. J. , Oerlemans J.
Published: May 2003

Glaciers have fluctuated in historic times and the length fluctuations of many glaciers are known. From these glacier length records, a climate reconstruction described in terms of a reconstruction of the equilibrium-line altitude (ELA) or the mass-balance can be extracted. In order to derive a climate signal from numerous glacier length records, a model is needed that takes into account the main characteristics of a glacier, but uses little information about the glacier itself. Therefore, a simple analytical model was developed based on the assumption that the change in glacier length can be described by a linear response equation. Historical length observations, the climate sensitivity and the response time of a glacier were needed to calculate historical equilibrium-line altitudes. Both climate sensitivity and length response time were calculated from a perturbation analysis on the continuity equation. The model was tested on 17 European glacier length records. The results revealed that the ELA of most glaciers increased on average 54 m between AD 1920 and 1950. The results of the analytical model were compared to mass-balance reconstructions calculated with a numerical flowline model and derived from historical temperature and precipitation records. The findings lead us to believe that the analytical model could be very useful to gain information about the historical mass-balance rates and ELAs.
Theoretical equilibrium-line altitudes and glacier buildup sensitivity in southern Norway based on meteorological data in a geographical information system
Authors: Lie Øyvind , Dahl Svein Olaf , Nesje Atle
Published: May 2003

Three equations derived from a close exponential glacier-climate relationship at the equilibrium-line altitude (ELA) of Norwegian glaciers have been utilized and implemented in a geographical information system (GIS). The first equation enables calculation of the minimum altitude of areas climatically suited for glacier formation at present, and is termed the altitude of instantaneous glacierization (AIG). Equation (2) is based on the ‘principle of terrain adaptation’, enabling quantification of the glacial buildup sensitivity (GBS) in an area. The third equation calculates the theoretical climatic (instrumental) temperature-precipitation ELA (CTP-ELA) in presently non-glaciated areas by combining GBS with terrain altitude. The presented approach is primarily intended for palaeoclimatic analyses of former glacial records, and is tested here based on a plot of 122 temperature stations and 197 precipitation stations during the climate normal period 1961-1990 which has been recalculated to sea level using empirical vertical climatic gradients. These data were interpolated in the GIS using an ‘inverse square interpolation’ routine. Subsequently, the interpolated climatic data were recalculated to the terrain surface using vertical climatic gradients and a digital elevation model (DEM) of southern Norway (resolution 5 X 5 degree minutes/c. 1 km2). The present glacier distribution in southern Norway is reproduced in great detail, and maps showing the modem GBS and CTP-ELA in non-glacierized areas of southern Norway are presented. Based on the GBS analysis, four scenarios with ELA depressions of 150 m (average ‘Little Ice Age’ conditions), 500 m (average coastal Younger Dryas conditions), 1000 m (suggested late Weichselian maximum coastal conditions) and 1500 m are shown.
Late-Holocene North Atlantic climate ‘seesaws’, storminess changes and Greenland ice sheet (GISP2) palaeoclimates
Authors: Dawson Alastair G. , Elliott Lorne , Mayewski Paul , Lockett Peter , Noone Sean , Hickey Kieran , Holt Tom , Wadhams Peter , Foster Ian
Published: May 2003

The oxygen-isotope record of palaeotemperature from Greenland ice cores has for many years been the kingpin of climate reconstructions for the North Atlantic region and northern Europe. An air temperature ‘seesaw’ between Greenland and northern Europe, first described in AD 1765, is also well known and is related to the North Atlantic Oscillation (NAO). Whereas the NAO index series is based on instrumental records of air pressure, the North Atlantic climate ‘seesaw’ has conventionally been based on air-temperature records. Here we describe relationships between this ‘seesaw’ mechanism and the Greenland (GISP2) oxygen-isotope chronology of air-temperature variations, as well as relationships between GISP2 Na+ (sea-salt) variations and instrumental records of North Atlantic storminess. The GISP2 proxy air-temperature record is calibrated for the last 130 years with instrumental weather records for West Greenland, while the Na+ series is compared with instrumental records of North Atlantic storminess change. Reconstruction of an annual series of these climate parameters for the last 1000 years shows that during the ‘Mediaeval Warm Period’ there were no years characterized by high Na+ extremes (high North Atlantic storminess) but there were many years when there were extremes of temperature. Remarkably, there were no years of exceptionally low air temperature and high Na+ precipitation at GISP2 between AD 1650 and 1710, a period of time that in northern Europe incorporates the period of maximum ‘Little Ice Age’ cooling. It would appear also that for the last thousand years the most extreme ‘seesaw’ winters when GISP2 temperatures were very low and Na+ concentrations were high occurred in discrete clusters and pairs of years.
Stable carbon- and hydrogen-isotope ratios of subfossil oaks in southern Germany: methodology and application to a composite record for the Holocene
Authors: Mayr Christoph , Frenzel Burkhard , Friedrich Michael , Spurk Marco , Stichler Willibald , Trimborn Peter
Published: May 2003

The &D and δ13C values of tree rings from dendrochronologically dated subfossil Holocene oaks have been studied for palaeoenvironmental and palaeoclimate reconstructions. The wood material mainly originates from fluvial deposits of the river Main and to a lesser extent from the Danube and Rhine regions in southern Germany. The chronology consists of the isotope records of 82 trees that cover a large part of the Holocene. The periods 8230 BC to AD 905 are represented by 6'13C values; AD values exist for the time interval 6470 BC to AD 905. Not all records have the same time resolution and not all of them were prepared in the same way for isotope analysis. However, investigations on the influence of the preparation technique on the isotope values and on the isotope composition of different wood compartments (latewood and earlywood, respectively) allowed us to homogenize the records. The comparison of δD values of wood with different cambial ages showed that hydrogen-isotoperatios were affected by growth trends. The uniformity of the trends implies physiological rather than microclimatic causes of these δD growth trends. The growth trends were corrected by subtracting a standardized trend curve, which in most cases resulted in a higher conformity in the overlap of tree-ring sequences. The δ13C records showed no uniform trends. However, the differences between δ13C values of overlapping trees in several cases were markedly offset, making it difficult to interpret the δ13C long-term trends in some sections of the chronology. Despite that, there are some characteristics common to both isotope chronologies. Most noticeable is the occurrence of comparatively high values in the interval 4500 to 2000 BC indicating higher temperatures (δD) and possibly lower water availability (δ13C), and a decrease in both isotope chronologies since about 2000 BC.
Mid-Holocene warming in the northwest Kola Peninsula, Russia: northern pine-limit movement and stable isotope evidence
Authors: Boettger Tatjana , Hiller Achim , Kremenetski Konstantin
Published: May 2003

A set of 40 subfossil Scots pines (Pinus sylvestris L.) was sampled in small lakes beyond the modernpine limit in the northwest Kola Peninsula, Russia. Radiocarbon dating suggests that the pine expanded north of its present-day limit between 7000 and 3500yr BP. The most extensive occurrence of pine forests was reconstructed between 6250 and 5750 yr BP. Numerous samples collected from trunks and stubs in situ clearly indicate lower lake levels between 6200 and 4400 yr BP. Living and 14C dated subfossil pine samples were analysed for the mean carbon, oxygen and hydrogen stable isotope composition of their wood cellulose. The mean δ13C, δ18O and δ2H values of the wood samples from the mid-Holocene time are C. 1.1%, 0.9% and lock, respectively - more positive than those of living trees in this region. These results suggest that the mid-Holocene climate in the region was warmer and drier than nowadays. The data agree with previous palynological, macrofossil and limnological studies from northernmost Fennoscandia. During the late-Holocene climatic deterioration after c. 3500 yr BP, the decline of the northern pine limit was synchronous with other parts of northern Eurasia. Comparison with dated pine series from the north-central Kola Peninsula and Finnish Lapland suggests that the decline of the northernmost pine limit in the eastern part of the area may have occurred somewhat earlier than in the western part.
Salinity changes in the central Baltic Sea (NW Europe) over the last 10000 years
Authors: Emeis Kay-Christian , Struck Ulrich , Blanz Thomas , Kohly Alexander , Voβ Maren
Published: May 2003

We attempt a reconstruction of salinity levels of the central Baltic Sea based on diatom assemblages, the isotopic composition of organic matter and sedimentological expression of anoxia over the last 10 000 years. We use the data to investigate the dependence of salinity levels on climate evolution and isostasy. Changes in salinity of surface and deep waters were most pronounced from 8400 to approximately 5000 cal. BP. Density stratification between salty deep and fresher surface waters caused the frequent development of anoxic conditions and deposition of laminated sediments on large parts of the sea floor in the central Baltic Sea, and dramatic changes in organic carbon-accumulation rates. From 5000 to 3100 cal. BP, the salinity of the basin decreased, oxygenation of deep sea floors was improved, and fertility of the sea surface was significantly reduced. This is reflected by low accumulation rates of organic carbon in bioturbated sediments. Since 2800 cal. BP, salinity rose again and anoxic periods were more common. Even though the major steps in environmental evolution in the Baltic Sea coincide with known patterns of climatic change of the North Atlantic realm over the last 10 000 years, we find no conclusive evidence for synchronous changes or linear responses on submillennial timescales. However, we note that major variations in our salinity records agree with temporal patterns of reconstructed summer warmth and winter precipitation in southern Scandinavia. Both types of record suggest that climate in the mid-Holocene was far from stable. Our data also confirm that climate evolution over the late Holocene had significant impact on environmental conditions in the Baltic Sea.
Lateglacial and Holocene environmental changes in Portuguese coastal lagoons 1: the sedimentological and geochemical records of the Santo André coastal area
Authors: Maria da Conceição Freitas  , Andrade César , Rocha Fernando , Tassinari Colombo , Munhá José Manuel , Cruces Anabela , Vidinha Jesus , Carlos Marques da Silva
Published: May 2003

The sedimentological and geochemical study of a core corresponding to sedimentation in the Santo André lowland since 14 000 BP allowed the reconstruction of environmental changes of this area and discussion of the relative importance of local versus global forcing factors responsible for its evolution. The pre-Holocene section of the core represents terrestrial sedimentation in a fluviatile environment, contemporaneous of a low sea level and a distal shoreline. Sediment inputs were terrestrial and resulting from intensive weathering and high erosion rate in the adjacent watershed. During the Early Holocene ( c. 10 020 to 5380 BP) the sea invaded this lowland and defined an open marine shallow environment corresponding to a wide gulf which has been disturbed by multiple terrestrial inputs that might have been induced by massive episodes of fluvial discharge. The first symptoms of confinement were noticed close to 5400 BP, and c. 5380 BP a major environmental threshold occurred (possibly reflecting the marked deceleration of the sea-level rise rate) corresponding to the establishment of an efficient detrital barrier that completely isolated the bay and changed this lowland into a closed coastal lagoon. After 5380 BP, the lagoonal environment evolved as a function of local forcing factors, among which the frequency and efficiency of exchanges with the ocean predominate: until c. 3570 BP the lagoon was restricted, fed by fresh water and terrestrial sediment inputs; a second episode of lagoonal sedimentation lasts until c. 1620 BP, reflecting brackish conditions and increase in marine influence due to a reduced efficiency of the barrier. The upper section of the core represents the final stages of filling of the lagoonal margin by fluvial activity. Human settling and intervention in the barrier are possible causes of a short-lived return to brackish conditions recorded in the uppermost sediment unit of the core and of the dramatic increase of the sedimentation rates
Lateglacial and Holocene environmental changes in Portuguese coastal lagoons 2: microfossil multiproxy reconstruction of the Santo André coastal area
Authors: Cearreta Alejandro , Cachão Mário , Cabral M. Cristina , Bao Roberto , Maria de Jesus Ramalho
Published: May 2003

Benthic foraminiferal, ostracod, calcareous nannoplankton and diatom assemblages have been analysed from the 25.45 sedimentary succession of a borehole drilled in the Santo André lagoon (southwestern Portugal). The zones and subzones recognized according to their microfossil content have been used to define six palaeoenvironmental stages extending from the Lateglacial to the present. Stage A and the lower part of stage B (14.2 to 10.0 ka) represent a postglacial terrestrial environment when sea level was below present. Following eustatic sea-level rise, a normal marine, open-bay environment established during the upper part of stage B (10.0 to 5.4 ka). Before 5.4 ka, a coastal lagoon developed as a consequence of a sandy barrier formation. Since then, natural variation in the permeability of the detrital barrier through time has been the primary control of the physical, chemical and biological features of the lagoonal environment: during stage C (5.4 to 3.6 ka) as a freshwater-dominated lagoon, stage D (3.6 to 1.6 ka) as a brackish lagoonal environment, and stage E (1.6 to 0.5 ka) as a return to a freshwater-dominated lagoon. Finally, in the last 400 years (stage F), human intervention on the sandy barrier (artificial open- and closed-inlet conditions) has provoked rapid and dramatic environmental changes in Santo André.
Lateglacial and Holocene environmental changes in Portuguese coastal lagoons 3: vegetation history of the Santo Andre coastal area
Authors: Santos Luisa , Goñi María Fernanda Śnchez
Published: May 2003

Pollen analysis from a well-dated sedimentary sequence of the Santo Andr6 lagoon (SW Portugal) reflects the vegetational and environmental changes that occurred during the Lateglacial and the Holocene in this coastal area. The Wtnrm/Weichselian Lateglacial interstadial was contemporaneous with a well-developed local Pinus forest. During the early Holocene (between 10 020 and 5300 yr BP), a Mediterranean forest with Pinus colonized the Santo Andre basin. After 5300 yr BP the local development of Alnus, Salix and aquatic plants suggests the development of freshwater ponds as a consequence of the formation of a coastal barrier. Contemporaneously, the expansion of evergreen Quercus, which partially replaced the Pinus forest, suggests a regional drying trend at c. 5000 yr BP, a change also observed elsewhere in southern Iberia.
Interaction of alcohol and drugs in fatal poisonings
Authors: Koski Anna , Ojanperä Ilkka , Vuori Erkki
Published: May 2003

In Finnish data from 1995 / 2000, 1006 fatal poisonings due to alcohol (ethanol), a single drug or both were statistically analysed in retrospect to evaluate the interaction between alcohol and drugs. In 53% of these cases, low concentrations of some common benzodiazepines were present. The median postmortem blood alcohol concentration (BAC) was 3.3 (w/w) in the 615 alcohol poisonings, but significantly lower, ranging from 1.3 to 1.7, when promazine, doxepin, amitriptyline or propoxyphene were found together with alcohol. When levomepromazine, temazepam or zopiclone were present, the median BAC was also significantly lower, 2.5 trations of a drug (excluding citalopram), suggesting a positive concentration / effect relationship. Fatal toxicity indices (FTIs) were calculated by relating the number of deaths caused by a drug to the corresponding sales figures. Promazine had an extremely high FTI, followed by levomepromazine, propoxyphene, doxepin and amitriptyline. The other drugs had relatively low FTIs. The results reflect not only the acute toxicity of a given drug / alcohol combination but also the manners of use and abuse of these drugs.
Spermatogenesis recovery in the mouse after iron injury
Authors: De Lourdes Pereira Maria , Costa Fernando Garciae
Published: May 2003

Alloys used as prosthetic devices for bone/joint replacement include some heavy metals such as chromium, iron, nickel, or titanium. Unfortunately, due to the aggressive nature of the physiological environment, corrosion of these alloys promotes the release of metal ions into the surrounding tissues causing systemic toxic effects. Our previous preliminary studies have demonstrated that iron induced several morphological changes within mice seminiferous epithelium. The aim of the present work was to investigate, over a one-month period, the possibility of recovery of mice seminiferous epithelium, previously damaged by iron. Male Charles River mice were dosed subcutaneously with 0.5 mL of an iron suspension of 538 mg/L9-10 10 mg/L (n-5) every 72 hours during two weeks, followed by a recovery period of 30 days. Fragments of the seminiferous tubules were fixed in glutaraldehyde and prepared for light and transmission electron microscopy. Regeneration of spermatogenesis was noted after a one-month period, as illustrated by the presence of normal germ cells, in the usual position within the seminiferous tubules. These germinal elements and the Sertoli cells have shown normal cytological features. These results strongly suggest that the deleterious effects induced by iron are reversible. The presence of residual bodies within Sertoli cells cytoplasm indicates that they are able to perform a normal functional activity in a recovered spermatogenesis.
Favourable influence of low molecular weight heparin in mitigating the peroxidative membrane damage induced by a cytotoxic agent and an atherogenic diet
Authors: Deepa P R , Varalakshmi P
Published: May 2003

The present study is aimed to demonstrate the protective effect of a heparin derivative, low molecular weight heparin (LMWH) against erythrocyte membrane injury. Two models serve to induce membrane lipid peroxidative damage, namely a potent cytotoxic agent, adriamycin and a hypercholesterolemic atherogenic diet. Two groups of male Wistar rats (1409-10 g) received a single intravenous injection of adriamycin (ADR, 7.5 mg/kg), while two other groups were fed an atherogenic diet comprising a supplementation of 4% cholesterol, 1% cholic acid and 0.5% thiouracil (CCT diet) for 2 weeks. For each of the above two groups, LMWH (Troparin; 300 mg/day per rat subcutaneously) treatment commenced on day 8 and continued for a week. One group was maintained as the normal control group, and another group that received only LMWH treatment was designated as the LMWH drug control group. Erythrocyte membrane was isolated and assayed for its cholesterol levels, lipid peroxidation and ATPases activity. The activities of antioxidant enzymes were assessed in the haemolysate. The findings of the study were that both adriamycin and the atherogenic diet produced elevated membrane cholesterol levels and lipid peroxidation. The membrane ATPases suffered loss in activity. Accentuated oxidative stress was marked by rise in the activities of antioxidant enzymes (SOD, catalase and GPx). LMWH intervention reverted these changes thereby normalizing the membrane composition and function. The membrane protective effect of LMWH is illuminated by this work.
Changes in plasma lipids after a non-lethal dose of cycloheximide in rats
Authors: Lucić A , Bradamante V , Peraica M , Radić B , Domijan A-M , Fuchs R
Published: May 2003

This paper describes a study of the effect of a single intraperitoneal non-lethal dose of cycloheximide (CHM; 2.0 mg/kg body weight) on the concentration of plasma lipids and lipoproteins in male rats killed one, two, three, four and nine days after receiving the dose. The concentration of triglycerides, total cholesterol, high-density lipoproteins (HDL)-cholesterol and low-density lipoproteins (LDL)-cholesterol was measured in treated and control animals. The effect of CHM on the concentration of triglycerides, total cholesterol, HDL-cholesterol, and LDL-cholesterol was visible in rat plasma throughout the study. Total cholesterol and HDL-cholesterol concentrations showed the same pattern of changes, probably due to the reversible inhibition of apolipoprotein apo A-I synthesis by CHM. The concentration of triglycerides decreased after a lag period of three days when the reserves of apolipoprotein apo B, the main apolipoprotein of very low-density lipoproteins (VLDL)-cholesterols produced in the liver, were consumed.
Differential responses of rat alveolar macrophages to carpet dust in vitro
Authors: Ameen Mohamed , Ahmad Iqbal , Musthapa Syed , Baig Masroor Alam , Mishra Rinky , Rahman Qamar
Published: May 2003

Epidemiological studies of workers in carpet weaving units in carpet industries have shown a direct relation between the concentration of carpet dust in the air and respiratory symptoms. To predict the health risk of carpet weavers, this preliminary study was conducted to evaluate the toxic potential of different types of workplace dust by using alveolar macrophages (AMs). Several parameters were observed for cytotoxicity such as cell viability, the release of lactate dehydrogenase (LDH) in rat AMs treated with different concentration of carpet dust and haemolytic potential of erythrocytes. In addition, reactive oxygen/nitrogen species-inducing effects of carpet dust were assessed by nitric oxide (NO), reduced glutathione (GSH) release and hydrogen peroxide (H2O2) generation in AMs. Results of cell viability and hemolytic assay showed a direct correlation between increasing the dust concentration with enhancing the toxic effect. Knotted and tufted carpet dust increases the release of LDH, NO, GSH and H2O2 production with increasing dust concentration. Present observations have revealed that dusts collected from tufted carpet weaving units exhibited more toxicity to AMs than knotted carpet dust. These data further suggest that injurious effects of carpet dust to AMs could pave a way to evaluate the toxic potential of the different types of workplace dusts and component(s) involved in it.
Protective role of DLa-lipoic acid against adriamycin-induced cardiac lipid peroxidation
Authors: Balachandar A V , Malarkodi K P , Varalakshmi P
Published: May 2003

The cytoprotective activity of a-lipoic acid against free radical toxicity manifested during adriamycin (ADR)induced cardiotoxicity has been investigated. ADR is a potent antitumour drug known to cause severe cardiotoxicity. Although ADR generates free radicals, the role of these radicals in the development of cardiac toxicity is still not well understood. In the present study, we evaluated the influence of chronic ADR treatment on the cellular defence mechanism against free radicals and the effect of a-lipoic acid supplementation on ADR-induced cardiotoxicity in male Wistar rats. The increase in lipid peroxidation (LPO) and activities of serum myocardial enzymes, namely lactate dehydrogenase (LDH) and creatinephosphokinase, associated with the decrease in activities of enzymatic (SOD, CAT, GPx, G6PD and GR) and non-enzymatic (GSH, Vit C and Vit E) antioxidants levels were the salient features observed in ADR-induced cardiotoxicity. Lipoic acid pretreated groups showed significant increase in activities of both enzymatic and non-enzymatic antioxidant levels. These observations highlight the antioxidant property ofa-lipoic acid and its cytoprotective action against ADR-induced cardiotoxicity.
Acute lead exposure induces renal haeme oxygenase-1 and decreases urinary Na excretion
Authors: Vargas Hilda , Castillo Carlos , Posadas Francisco , Escalante Bruno
Published: May 2003

The effects of acute lead exposure on renal function, lipid peroxidation and the expression of haeme oxygenase (HO) in rat kidney were determined. A single injection of lead acetate (50 mg Pb/kg) was given to rats. Changes in renal function, characterized by a significant reduction in the Na excretion was observed six hours after Pb exposure; this effect persisted for 24 hours. TBARS levels increased in kidney cortex 24 hours after Pb administration. In kidney cortex, Pb exposure affected the expression of HO-1, a renal protein associated with oxidative stress. HO-1 mRNA increased 2.3-fold, three hours after Pb administration and remained increased for six, 12 and 24 hours. HO enzymatic activity and HO-1 protein increased six and three hours after Pb administration, respectively, and remained increased at 24 hours. HO inhibition by tin-protoporphyrin, potentiated Pb-induced increase in TBARS and prevented the Pb-induced reduction in Na excretion. Our data suggest that Pb may be acting through the generation of oxidant products and induction of HO.
The role of the cytoskeleton in mechanotransduction in human osteoblastlike cells
Authors: Rosenberg Nahum
Published: May 2003

The regulation of osteoblast proliferation is a key factor in maintaining bone mass. The enhancement of this process can be achieved by stimulating the proliferation of these cells. Mechanical stimulation is one of the important enhancing factors, but the exact cellular mechanisms of mechanical stimulation, i.e., mechanotransduction, are unknown. In order to investigate the role of the cytoskeleton components in mechanotransduction for cell proliferation, I compared the total DNA content in cultured replicates of osteoblast-like cells derived from three human donors following their exposure to enhancing mechanical stimulation, with and without added specific microtubular and microfilament polymerization blockers (Colchicin and Cytochalasin D, respectively). The results revealed the essential and unique role of the microtubular component of the cytoskeleton in mechanotransduction for proliferation by showing that Colchicin blocked the expected increase in the DNA content after mechanical stimulation of the cultured replicates without altering the total DNA content in replicates at static conditions. Conversely, a specific blockage of the microfilament polymerization presented uniform cytotoxic effect in both static and biomechanically active environments. Since previous reports indicated the essential role of microfilament polymerization for the osteoblast metabolic activity, the results of this study further support the hypothesis that the mechanotransduction mechanisms for proliferation and metabolic activity are mediated by different intracellular pathways.
Accurate bounds for the asymptotic constant in a statistical multiplexer with homogeneous generalized binary Markov sources
Authors: Xue J. , Alfa Attahiru Sule
Published: May 2003

This paper considers the asymptotic tail distribution of the number of cells queued in a statistical multiplexer fed with homogeneous generalized binary Markov sources. As the asymptotic decay rate is easy to obtain, we focus our effort on bounding the asymptotic constant, which is dependent on the initial phase combination of the sources and is hard to compute even for a moderate number of sources. We derive upper and lower bounds for the asymptotic constant, taking the initial phase combination into account. Numerical experiments show the accuracy of these bounds. They also show that, while the asymptotic decay rates are the same, the variation of initial phase combination of the sources may significantly affect the asymptotic constants.
Polling systems with periodic server routeing in heavy traffic: distribution of the delay
Authors: Olsen Tava Lennon , van der Mei R. D.
Published: May 2003

We consider polling systems with mixtures of exhaustive and gated service in which the server visits the queues periodically according to a general polling table. We derive exact expressions for the steady-state delay incurred at each of the queues under standard heavy-traffic scalings. The expressions require the solution of a set of onlyM—Nlinear equations, whereMis the length of the polling table andNis the number of queues, but are otherwise explicit. The equations can even be expressed in closed form for several routeing schemes commonly used in practice, such as the star and elevator visit order, in a general parameter setting. The results reveal a number of asymptotic properties of the behavior of polling systems. In addition, the results lead to simple and fast approximations for the distributions and the moments of the delay in stable polling systems with periodic server routeing. Numerical results demonstrate that the approximations are highly accurate for medium and heavily loaded systems.
Zero-sum games for continuous-time Markov chains with unbounded transition and average payoff rates
Authors: Guo Xianping , Hernández-Lerma Onésimo
Published: May 2003

This paper is a first study of two-person zero-sum games for denumerable continuous-time Markov chains determined by given transition rates, with an average payoff criterion. The transition rates are allowed to be unbounded, and the payoff rates may have neither upper nor lower bounds. In the spirit of the ‘drift and monotonicity’ conditions for continuous-time Markov processes, we give conditions on the controlled system's primitive data under which the existence of the value of the game and a pair of strong optimal stationary strategies is ensured by using the Shapley equations. Also, we present a ‘martingale characterization’ of a pair of strong optimal stationary strategies. Our results are illustrated with a birth-and-death game.
Stochastic ordering for continuous-time processes
Authors: Irle A.
Published: May 2003

We consider the following ordering for stochastic processes as introduced by Irle and Gani (2001). A process (Yt)t is said to be slower in level crossing than a process (Zt)t if it takes (Yt)t stochastically longer than (Zt)t to exceed any given level. In Irle and Gani (2001), this ordering was investigated for Markov chains in discrete time. Here these results are carried over to semi-Markov processes with particular attention to birth-and-death processes and also to Wiener processes.
Poisson approximation of multivariate Poisson mixtures
Authors: Roos Bero
Published: May 2003

We show how good multivariate Poisson mixtures can be approximated by multivariate Poisson distributions and related finite signed measures. Upper bounds for the total variation distance with applications to risk theory and generalized negative multinomial distributions are given. Furthermore, it turns out that the ideas used in this paper also lead to improvements in the Poisson approximation of generalized multinomial distributions.
Urn models and differential algebraic equations
Authors: Higueras I. , Moler J. , Plo F. , San Miguel M.
Published: May 2003

The aim of this paper is to study the distribution of colours, {Xn}, in a generalized Pólya urn model with L colours, an urn function and a random environment. In this setting, the number of actions to be taken can be greater than L, and the total number of balls added in each step can be random. The process {Xn} is expressed as a stochastic recurrent equation that fits a Robbins—Monro scheme. Since this process evolves in the (L—1)-simplex, the stability of the solutions of the ordinary differential equation associated with the Robbins—Monro scheme can be studied by means of differential algebraic equations. This approach provides a method of obtaining strong laws for the process {Xn}.
An improved approximation for assessing the statistical significance of molecular sequence features
Authors: Mercier S. , Cellier D. , Charlot D.
Published: May 2003

Using random walk theory, we first establish explicitly the exact distribution of the maximal partial sum of a sequence of independent and identically distributed random variables. This result allows us to obtain a new approximation of the distribution of the local score of one sequence. This approximation improves the one given by Karlin et al., which can be deduced from this new formula. We obtain a more accurate asymptotic expression with additional terms. Examples of application are given.
On the uniform ergodicity of Markov processes of order 2
Authors: Herkenrath Ulrich
Published: May 2003

We study the uniform ergodicity of Markov processes (Zn, n ≥ 1) of order 2 with a general state space (Z, 𝒵). Markov processes of order higher than 1 were defined in the literature long ago, but scarcely treated in detail. We take as the basis for our considerations the natural transition probability Q of such a process. A Markov process of order 2 is transformed into one of order 1 by combining two consecutive variables Z2n–1 and Z2n into one variable Yn with values in the Cartesian product space (Z × Z, 𝒵 ⊗ 𝒵). Thus, a Markov process (Yn, n ≥ 1) of order 1 with transition probability R is generated. Uniform ergodicity for the process (Zn, n ≥ 1) is defined in terms of the same property for (Yn, n ≥ 1). We give some conditions on the transition probability Q which transfer to R and thus ensure the uniform ergodicity of (Zn, n ≥ 1). We apply the general results to study the uniform ergodicity of Markov processes of order 2 which arise in some nonlinear time series models and as sequences of smoothed values in sequential smoothing procedures of Markovian observations. As for the time series models, Markovian noise sequences are covered.
Preservation of generalized bathtub-shaped functions
Authors: Savits Thomas H.
Published: May 2003

Block, Savits and Singh previously presented a preservation result for bathtub-shaped functions. In this paper, we strengthen and extend their results to a class of functions which allow for more than one change of monotonicity. Various applications are also considered.
Mixtures of distributions with increasing linear failure rates
Authors: Block Henry W. , Savits Thomas H. , Wondmagegnehu Eshetu T.
Published: May 2003

Populations of specific components are often heterogeneous and consist of a small number of different sub-populations. For example there are often two groups: defective components with shorter lifetimes and standard components with longer lifetimes. Another heterogeneous population results when components produced by two different manufacturing lines are combined. In either case a mixture results. The resulting population can be described using the statistical concept of a mixture. It is a well-known result that a mixture of distributions with decreasing failure rates has a decreasing failure rate. However, little is known about the monotonicity of a mixture when the various subpopulations have failure rates which are not necessarily decreasing. In this paper we study and attempt to determine the shape as well as the overall behavior of the failure rate of a mixture from two subpopulations each of which has increasing linear failure rate.
The coupon-collector's problem revisited
Authors: Adler Ilan , Oren Shmuel , Ross Sheldon M.
Published: May 2003

Consider the classical coupon-collector's problem in which items of m distinct types arrive in sequence. An arriving item is installed in system i ≥ 1 if i is the smallest index such that system i does not contain an item of the arrival's type. We study the expected number of items in system j at the moment when system 1 first contains an item of each type
Average cost under the PMλ, τ policy in a finite dam with compound Poisson inputs
Authors: Bae Jongho , Kim Sunggon , Lee Eui Yong
Published: May 2003

We consider the policy in a finite dam in which the input of water is formed by a compound Poisson process and the rate of water release is changed instantaneously from a to M and from M to a (M > a) at the moments when the level of water exceeds λ and downcrosses τ (λ > τ) respectively. After assigning costs to the changes of release rate, a reward to each unit of output, and a cost related to the level of water in the reservoir, we determine the long-run average cost per unit time.
Polymorphism of the rod visual pigment between allopatric populations of the sand goby (Pomatoschistus minutus): a microspectrophotometric study
Authors: Jokela Mirka , Vartio Annika , Paulin Lars , Fyhrquist-Vanni Nanna , Donner Kristian
Published: June 2003

Absorbance spectra were measured by microspectrophotometry in retinal rods of sand gobies (Pomatoschistus minutus) from four allopatric populations (Baltic Sea, Swedish west coast, English Channel and Adriatic Sea). Mean (± s.e.m.) wavelengths of maximum absorbance (λmax) were 508.3±0.5 nm,505.4±0.2 nm, 506.2±0.3 nm and 503.0±0.3 nm,respectively. Pairwise comparison between the populations (post-ANOVA Scheffe's test) shows that each of the λmax differences,except that between the Swedish west coast and the English Channel, is statistically significant (P<0.05). The shapes of the absorbance spectra indicated that the pigments were A1 rhodopsins with no measurable admixture of the A2 chromophore. Thus, the differences indicate polymorphism in the protein part (opsin) of the pigment. Convolution of A1 templates forλ max values 508.3 nm and 503.0 nm with quantum spectra of the downwelling light at two locations at the south-west coast of Finland indicated that a 13-19% improvement in quantum catch would accrue in the Baltic environment from the 5.3 nm red-shift of the rod pigment of Baltic compared with Adriatic sand gobies.
The funding and organization of infection control in NHS hospital trusts: a study of infection control professionals' views
Authors: Croxson B. , Allen P. , Roberts J. A. , Archibald K. , Crawshaw S. , Taylor L.
Published: May 2003

The problems associated with hospital-acquired infection have been causing increasing concern in England in recent years. This paper reports the results of a nationwide survey of hospital infection control professionals' views concerning the organizational structures used to manage and obtain funding for control of infection. A complex picture with significant variation between hospitals emerges. Although government policy dictates that specific funding for hospital infection control is formally made available, it is not always the case that infection control professionals have adequate resources to undertake their roles. In some cases this reflects the failure of hospitals' infection control budgetary mechanisms; in others it reflects the effects of decentralizing budgets to directorate or ward level. Some use was made of informal mechanisms either to supplement or to substitute for the formal ones. But almost all infection control professionals still believed they were constrained in their ability to protect the hospital population from the risk of infectious disease. It is clear that recent government announcements that increased effort will be made to support local structures and thereby improve the control of hospital acquired infection are to be welcomed.
Perceived access in a managed care environment: determinants of satisfaction
Authors: Akinci F. , Sinay T.
Published: May 2003

With increasing competition in the local and regional healthcare markets, and growing interest in assessing the effectiveness of services and patient outcomes, satisfaction measures are becoming prominent in evaluating the performance of the healthcare system. This study examines the independent effect of predisposing, enabling and medical need factors on perceived access to care with particular focus on insurance plans. A survey questionnaire is developed to investigate access limitations at three levels: (1) the health plan, (2) the individual provider(s) and (3) the healthcare organization. In addition, shortage of providers, residents' perceptions of their health status, satisfaction with access to care and socio-demographic indicators are incorporated into the analysis. Multivariate logistic regression is used to assess the independent effects of the above factors on a dichotomous dependent variable - residents' overall satisfaction with access to healthcare services. The most salient determinants of overall satisfaction with access to care were the type of health insurance plan, cost of insurance premiums, co-payments, difficulty with obtaining referrals, self-rated general health, the opportunity cost of taking time to see a provider (measured by the loss of hourly wages), marital status and the age factor over 80 years.
Tools of the trade: a comparative analysis of approaches to priority setting in healthcare
Authors: Mitton C. , Donaldson C.
Published: May 2003

In many countries, local managers and clinicians have been given responsibility to set health priorities and allocate resources accordingly. Although tools have been suggested for use in aiding this process, knowledge of these tools within health regions is lacking and comparative analysis in the literature is limited. Several approaches to priority setting are critiqued from both practical and theoretical perspectives, and a tangible way forward for such activity is provided. The approaches analysed include: needs assessment, core services, economic evaluation including quality-adjusted life year league tables, and programme budgeting and marginal analysis (PBMA). Needs assessment fails to recognize underlying economic principles of opportunity cost and the margin, while core services ignores the margin and has had limited impact in practice. Economic evaluations can consider marginal costs and benefits, but cannot always be used to inform decisions in a timely manner. PBMA is based on underlying economic principles and can pragmatically respond to objectives related to both efficiency and equity. Although PBMA is not without challenges, from an economic perspective, it does seem to 'get the thinking right', and, importantly, as a process, can incorporate some of the other approaches to priority setting discussed in this paper.
Barriers to evidence-based decision making among Polish healthcare managers
Authors: Niedźwiedzka B. M.
Published: May 2003

The 1999 reform of the Polish healthcare system revealed deficiencies in the research base and a lack of organized systems of information provision. Professionals who most need effective information systems are policymakers and healthcare managers. The main aim of the described study was to obtain data describing the needs, preferences and limitations of healthcare managers as information users, and to identify environmental factors influencing their information behaviour. A national postal survey was conducted and supplemented with information collected during focus groups, semi-structured interviews and through analysis of relevant policy documents. The target population included hospital chief executives, medical directors, head nurses and directors of the institutions responsible for health services planning and purchasing. Target institutions were drawn systematically from official lists, stratified by regions of the country and hospital reference level. The interviews were conducted with primary care unit managers and with Ministry of Health officials. National health strategy and directives, cost-effectiveness analyses of interventions and clinical practice guidelines emerged as information of primary importance to respondents. The main barriers to effective information behaviour were found to be: attitudes towards research activity, lack of appropriately processed data, lack of skills enabling information seeking and appraisal, inappropriate format of publications, ineffective dissemination of information and absence of services facilitating access to evidence. The current information environment of healthcare managers, together with their attitude towards information and deficiencies in information skills, appear to serve as a barrier to evidence-based practice in the Polish healthcare system.
Why is high-tech healthcare at home purchasing underdeveloped and what could be done to improve it?
Authors: Short D. , Norwood J.
Published: May 2003

Executive Letter (95)5 initiated a change of health policy preventing general practitioners (GPs) from prescribing packages of 'high-tech healthcare at home' (HTHC). From 1 April 1995, district health authorities were required to establish contracts to purchase such care. Several reasons were behind this policy change including the belief that contracting would improve service quality by encouraging competition between potential suppliers, securing better value for money, and establishing service specifications and monitoring mechanisms. Our survey of 98 health authorities, however, highlighted that contracting for home total parenteral nutrition, intravenous antibiotics for patients with cystic fibrosis, intravenous chemotherapy and continuous ambulatory peritoneal dialysis is largely undeveloped. The majority of districts contracted with historic providers and authorities freely admitted that they did not know whether they were obtaining value for money or a service of adequate quality. Only three districts had developed a strategy for purchasing HTHC as required by the Executive Letter, and only 17 had plans to re-examine their approach. Contracting for HTHC presents practical problems, including the complexity of the process and the significant time demands for efficient and effective contracting. Phase two of this research sought to produce a 'guide to good practice' for health authorities wishing to re-examine and improve their purchasing. We conducted case study analyses in districts that had made effective progress and those that had encountered difficulties, drawing upon lessons learned. We reported our findings to the NHS Executive and supplemented this with a 'toolbox' that included sample documents covering areas such as tendering, monitoring mechanisms, service specifications and different purchasing approaches.