bluuebunny/crossref_metadata_2025 huggingface dataset:
Additive and multiplicative covariate regression models for relative survival incorporating fractional polynomials for time‐dependent effects
Authors: Lambert Paul C. , Smith Lucy K. , Jones David R. , Botha Johannes L.
Published: November 2005

Relative survival is used to estimate patient survival excluding causes of death not related to the disease of interest. Rather than using cause of death information from death certificates, which is often poorly recorded, relative survival compares the observed survival to that expected in a matched group from the general population. Models for relative survival can be expressed on the hazard (mortality) rate scale as the sum of two components where the total mortality rate is the sum of the underlying baseline mortality rate and the excess mortality rate due to the disease of interest. Previous models for relative survival have assumed that covariate effects act multiplicatively and have thus provided relative effects of differences between groups using excess mortality rate ratios. In this paper we consider (i) the use of an additive covariate model, which provides estimates of the absolute difference in the excess mortality rate; and (ii) the use of fractional polynomials in relative survival models for the baseline excess mortality rate and time‐dependent effects. The approaches are illustrated using data on 115 331 female breast cancer patients diagnosed between 1 January 1986 and 31 December 1990. The use of additive covariate relative survival models can be useful in situations when the excess mortality rate is zero or slightly less than zero and can provide useful information from a public health perspective. The use of fractional polynomials has advantages over the usual piecewise estimation by providing smooth estimates of the baseline excess mortality rate and time‐dependent effects for both the multiplicative and additive covariate models. All models presented in this paper can be estimated within a generalized linear models framework and thus can be implemented using standard software. Copyright © 2005 John Wiley & Sons, Ltd.
Analysis of time‐dependent covariates in a regressive relative survival model
Authors: Giorgi Roch , Gouvernet Joanny
Published: November 2005

Relative survival is a method for assessing prognostic factors for disease‐specific mortality. However, most relative survival models assume that the effect of covariate on disease‐specific mortality is fixed‐in‐time, which may not hold in some studies and requires adapted modelling. We propose an extension of the Esteveet al.regressive relative survival model that uses the counting process approach to accommodate time‐dependent effect of a predictor's on disease‐specific mortality. This approach had shown its robustness, and the properties of the counting process give a simple and attractive computational solution to model time‐dependent covariates. Our approach is illustrated with the data from the Stanford Heart Transplant Study and with data from a hospital‐based study on invasive breast cancer. Advantages of modelling time‐dependent covariates in relative survival analysis are discussed. Copyright © 2005 John Wiley & Sons, Ltd.
A case study in comparing therapies involving informative drop‐out, non‐ignorable non‐compliance and repeated measurements
Authors: Härkänen T. , Knekt P. , Virtala E. , Lindfors O.
Published: November 2005

Virtually no comparisons of different psychotherapies with long follow‐up times have been carried out until now. The Helsinki Psychotherapy Study is a randomized clinical trial, where patients were monitored for 12 months after the onset of study treatments, of which each lasted approximately 6 months. The patients' psychiatric status was measured at five pre‐determined time points during the follow‐up period. In general, the analyses of trials are complicated in cases where compliance with the given treatment is incomplete or the drop‐out from the follow‐up is non‐ignorable. In the present study, the quality of the treatment deviated from the protocol for some patients and some patients took auxiliary treatments which had similar effects to the study treatment during the study treatment or follow‐up period. This might have resulted in standard intention‐to‐treat analyses providing excessively conservative or liberal conclusions. Non‐compliance may have been non‐ignorable in some cases, so subject‐specific latent factors may have influenced the outcome both directly and indirectly via compliance behaviour. The most and least healthy patients are the most likely to dropout from the follow‐up a priori, so the missing data process is informative. The missing data can partly be augmented with surrogate information collected during interviews with patients who dropped out. A Bayesian hierarchical as‐treated model, which uses random‐effects‐based selection models to account for non‐ignorable missing data and non‐compliance, was compared with different mixed effects models. Copyright © 2005 John Wiley & Sons, Ltd.
Goodness of fit of relative survival models
Authors: Stare Janez , Pohar Maja , Henderson Robin
Published: November 2005

Additive regression models are preferred over multiplicative models in the analysis of relative survival data. Such preferences are mainly grounded in practical experience with mostly cancer registries data, where the basic assumption of the additivity of hazards is more likely to be met. Also, the interpretation of coefficients is more meaningful in additive than in multiplicative models. Nonetheless, the question of goodness of fit of the assumed model must still be addressed, and while there is an abundance of methods to check the goodness of fit of multiplicative models, the respective arsenal for additive models is almost empty. We propose here a variety of procedures for testing the null hypothesis of a good fit. These are based on partial residuals defined similarly to Schoenfeld residuals familiar for Cox model diagnostics. The tests have appropriate sizes under the null hypothesis, and good power under different alternatives. We investigate their performance through simulations and apply the methods to data from a study into survival of colon cancer patients. Copyright © 2005 John Wiley & Sons, Ltd.
Meta‐analysis of heterogeneously reported trials assessing change from baseline
Authors: Abrams Keith R. , Gillies Clare L. , Lambert Paul C.
Published: November 2005

This paper considers the quantitative synthesis of published comparative study results when the outcome measures used in the individual studies and the way in which they are reported varies between studies. Whilst the former difficulty may be overcome, at least to a limited extent, by the use of standardized effects, the latter is often more problematic. Two potential solutions to this problem are; sensitivity analyses and a fully Bayesian approach, in which pertinent external information is included. Both approaches are illustrated using the results of two systematic reviews and meta‐analyses which consider the difference in mean change in systolic blood pressure and the difference in physical functioning between an intervention and control group. The two examples illustrate that by adopting a fully Bayesian approach, as opposed to undertaking sensitivity analyses assuming fixed values for unknown parameters, the overall intervention effect can be estimated with greater uncertainty, but that assessing the sensitivity of results to choice of prior distributions in such analyses is crucial. Copyright © 2005 John Wiley & Sons, Ltd.
A time‐dependent discrimination index for survival data
Authors: Antolini Laura , Boracchi Patrizia , Biganzoli Elia
Published: November 2005

To derive models suitable for outcome prediction, a crucial aspect is the availability of appropriate measures of predictive accuracy, which have to be usable for a general class of models. The Harrell'sCdiscrimination index is an extension of the area under the ROC curve to the case of censored survival data, which owns a straightforward interpretability. For a model including covariates with time‐dependent effects and/or time‐dependent covariates, the original definition ofCwould require the prediction of individual failure times, which is not generally addressed in most clinical applications. Here we propose a time‐dependent discrimination indexCtdwhere the whole predicted survival function is utilized as outcome prediction, and the ability to discriminate among subjects having different outcome is summarized over time.Ctdis based on a novel definition of concordance: a subject who developed the event should have a less predicted probability of surviving beyond his/her survival time than any subject who survived longer. The predicted survival function of a subject who developed the event is compared to: (1) that of subjects who developed the event before his/her survival time, and (2) that of subjects who developed the event, or were censored, after his/her survival time. Subjects who were censored are involved in comparisons with subjects who developed the event before their observed times. The index reduces to the previousCin the presence of separation between survival curves on the whole follow‐up. A confidence interval forCtdis derived using the jackknife method on correlated one‐sampleU‐statistics.

The proposed index is used to evaluate the discrimination ability of a model, including covariates having time‐dependent effects, concerning time to relapse in breast cancer patients treated with adjuvant tamoxifen. The model was obtained from 596 patients entered prospectively at Istituto Nazionale per lo Studio e la Cura dei Tumori di Milano (INT). The model discrimination ability was validated on an independent testing data set of 175 patients provided by Centro Regionale Indicatori Biochimici di Tumore (CRIBT) in Venice. Copyright © 2005 John Wiley & Sons, Ltd.
Evaluating technologies for classification and prediction in medicine
Authors: Pepe M. S.
Published: November 2005

Modern technologies promise to provide new ways of diagnosing disease, detecting subclinical disease, predicting prognosis, selecting patient specific treatment, identifying subjects at risk for disease, and so forth. Advances in genomics, proteomics and imaging modalities in particular hold great potential for assisting with classification/prediction in medicine. Before a classifier can be adopted for routine use in health care, its classification accuracy must be determined. Standards for evaluating new clinical classifiers however, lag far behind the well established standards that exist for evaluating new clinical treatments.

In this paper, we discuss a phased approach to developing a new classifier (or biomarker). It mirrors the internationally established phase 1–2–3 paradigm for therapeutic drugs. The defined phases lead to a logical sequence of studies for classifier development. We emphasize that evaluating classification accuracy is fundamentally different from simply establishing association with outcome. Therefore, study objectives and designs differ from the familiar methods of clinical trials. We discuss these briefly for each phase.

Finally, we argue that classifier development requires some rethinking of traditional data analysis techniques. As an example we show that maximizing the likelihood function to fit a logistic regression model to multiple predictors, can yield a poor classifier. Instead we demonstrate that an approach that maximizes an alternative objective function characterizing classification accuracy performs better. Copyright © 2005 John Wiley & Sons, Ltd.
Bayesian back‐calculation using a multi‐state model with application to HIV
Authors: Sweeting Michael J. , De Angelis Daniela , Aalen Odd O.
Published: November 2005

Back‐calculation is a method of obtaining estimates of the number of infections of a disease over time. Data on an endpoint of the disease, together with knowledge of the time from infection to endpoint, allows reconstruction of the incidence of infection. The technique has had much success when applied to the HIV epidemic, using incidence of AIDS diagnoses to inform past HIV infections. In recent years, the period from infection to AIDS has changed considerably due to new regimes of anti‐viral therapies. This has led to attempts to use incidence of first positive HIV test as an alternative basis for back‐calculation. Developing on earlier work, this paper explores the feasibility of a multi‐state formulation of the back‐calculation method that models the disease and diagnosis processes and uses HIV diagnoses as an endpoint. Estimation is carried out in a Bayesian framework, which naturally allows incorporation of external information to inform the diagnosis probabilities. The idea is illustrated on data from the HIV epidemic in homosexuals in England and Wales. Copyright © 2005 John Wiley & Sons, Ltd.
Grid support of a wind farm with active stall wind turbines and AC grid connection
Authors: Hansen Anca D. , Sørensen Poul , Iov Florin , Blaabjerg Frede
Published: November 2005

One of the main concerns in the grid integration of large wind farms is their ability to behave as active controllable components in the power system. This article presents the design of a new integrated power control system for a wind farm made up exclusively of active stall wind turbines with AC grid connection. The designed control system has the task of enabling such a wind farm to provide the best grid support. It is based on two control levels: a supervisory control level, which controls the power production of the whole farm by sending out reference signals to each individual wind turbine, and a local control level, which ensures that the reference power signals at the wind turbine level are reached. The ability of active stall wind farms with AC grid connection to control the power production to the reference power ordered by the operators is assessed and discussed by means of simulations. Copyright © 2005 John Wiley & Sons, Ltd.
X-Ray Diagnosis of Acute Scaphoid Fractures
Authors: CHEUNG G. C. , LEVER C. J. , MORRIS A. D.
Published: November 2005

In a retrospective review of the radiographs taken for 113 acute scaphoid fractures, each view was assessed for the clarity of demonstration of the fracture. The X-rays on which diagnosis of fracture were made, were taken between 0 and 16 days after injury (mean, 2 days). Whenever a lateral, supinated oblique or elongated view was taken, the fracture was always seen clearly on an alternative view. We recommend the use of four views at initial presentation of suspected scaphoid fracture: PA and lateral to assess carpal alignment, with pronated oblique and ulnar deviated PA to detect the fracture.
Stimulated Jitter Measurement in the Assessment of Recovery after different Methods of Peripheral Nerve Repair
Authors: LENIHAN D. V. , SOJITRA N. M. , GLASBY M. A.
Published: November 2005

The recording of stimulated jitter offers a quantitative method for following the recovery of neuromuscular function after peripheral nerve repair. In groups of rats, electrophysiological recording of jitter was carried out on control animals and on animals 90 days after sciatic nerve division and subsequent repair with either direct end-to-end suture (NS), nerve graft (NG) or freeze thawed muscle graft (FTMG). It was found that values for jitter were highest in the FTMG group. The NS and NG groups demonstrated statistically similar jitter values when compared with each other and with the normal. It was concluded that the speed of nerve regeneration is slower in the FTMG group, at least initially, and that 90 days after sciatic nerve repair the FMTG group had an increase in the number of immature neuromuscular junctions when compared with the NS or NG groups. Jitter measurement would appear to offer a means of detecting small differences in nerve regeneration. The value of this in future developments in nerve repair is discussed.
The Natural History of Post-Traumatic Reflex Sympathetic Dystrophy
Authors: ZYLUK A.
Published: November 2005

The paper presents the results of a prospective trial to examine the natural history of early reflex sympathetic dystrophy (RSD). Thirty patients with post-traumatic RSD of the hand were observed without treatment. They were reassessed 1, 2 and 6 months after diagnosis with a final assessment at 10 to 18 months (average 13 months). Twenty-seven patients completed the study. Three were withdrawn during the study because of persistence of signs and symptoms of RSD and were given further treatment. Of the 27 patients who completed the study, only one showed sufficient features of the condition to warrant the diagnosis of mild RSD. In the remaining 26, most features of RSD had resolved spontaneously. Pain and swelling disappeared more quickly than other features of RSD. Although the signs and symptoms of RSD had largely gone at 13 months, the hands were still functionally impaired because of weaker grip strength.
Conservative Versus Operative Treatment for Kienböck’s Disease
Authors: DELAERE O. , DURY M. , MOLDEREZ A. , FOUCHER G.
Published: November 2005

In this retrospective study on Kienböck’s disease, a comparison was made between 21 cases operated on by various techniques and 22 cases treated conservatively, with a mean follow-up of 65 months. Operative management of the disease did not show any superiority over conservative treatment. Moreover, surgery was responsible for a loss of mobility of 24%, and for a change in social activities in about a quarter of the patients, while grip strength was only slightly improved. Surgical indications for Kienböck’s disease should be carefully considered, keeping in mind their side-effects, and the relative benignity in some cases of the natural course of the disease.
The Effect of the Extent of A1 Pulley Release on the Force Required to Flex the Digits
Authors: LOW C. K. , PEREIRA B. P. , NG R. T. H. , LOW Y. P. , WONG H. P.
Published: November 2005

The A1 pulley was released distally in consecutive stages by 25%, 50%, 75% and 100% of its length. The force required to fully flex the digit at each stage was recorded. The force decreased with more extensive A1 pulley release and this became significant when more than 50% of the pulley was released. These changes were probably due to loss of friction force rather than bowstringing of the tendon.
The Motion Analysis System and the Fingertip Motion Area
Authors: CHIU H-Y. , SU F. C. , WANG S-T.
Published: November 2005

The reliability of the motion analysis system and the normal value of the fingertip motion area have been studied in young adults. The results indicate that the motion analysis system is a reliable tool for the evaluation of fingertip motion. It was found that the fingertip motion area in young adults has a linear correlation with the square of the finger length. Therefore, the normal value of the fingertip motion area can be calculated from the finger length.
Thumb Reconstruction by Pollicization of an Index Finger Stump Combined with a Wrap-Around Flap from the Big Toe
Authors: BARBATO B. D. , LEBLANC P. , LEMERLE J. P.
Published: November 2005

A finger stump pollicization combined with a thin wrap-around procedure from the big toe for reconstruction of the thumb is described. This technique permits excellent functional and cosmetic restoration, providing length to the new thumb as well as widening the first web. There is joint motion in the reconstructed thumb. Sensibility of the transferred pulp is good and allows fine pinch without pulp shrinkage. This method is indicated in cases of multidigit amputations, for thumb loss near the carpometacarpal joint.
Extended Wrap-Around Flap for Thumb Reconstruction following Radical Excision of a Congenital Arteriovenous Fistula
Authors: HATTORI Y. , DOI K. , KAWAKAMI F. , WATANABE M.
Published: November 2005

A 38-year-old woman presented with a large congenital arteriovenous fistula in her left hand with ischaemic atrophy of the thumb and index finger. Radical resection of the lesion and ray amputation of the index finger was done. To allow radical excision and reconstruction of the thumb and skin defect, we used an extended wrap-around flap. This flap is useful for primary reconstruction of the thumb following radical excision of a congenital arteriovenous fistula involving the thumb.
Biomechanical Properties of Absorbable Implants in Finger Fractures
Authors: FITOUSSI F. , LU W. , IP W. Y. , CHOW S. P.
Published: November 2005

The mechanical rigidity of five different methods of pin fixation in two proximal phalangeal fracture models was studied and absorbable implants were compared with metallic implants in a biomechanical cadaver study. Thirty phalanges were tested in apex palmar bending, compression and torsion. Results showed that rigidity of absorbable implants was comparable with metallic implants, except in torsion.
Solitary Dislocation of the Scaphoid
Authors: LEUNG Y. F. , WAI Y. L. , KAM W. L. , IP P. S.
Published: November 2005

Solitary dislocation of the scaphoid can be classified as simple, or complex if the distal carpal row is included. It may be total or partial. Partial dislocation of the proximal pole may occur in a radial, palmar or dorsal direction. Each type has a different significance in terms of surgical approaches, complications and prognosis.
Simultaneous Dislocation of the Scaphoid and Hamate Bones
Authors: SAKADA T. , NINOMIYA S. , OHMORI M.
Published: November 2005

We report a rare case of simultaneous dislocations of the hamate and scaphoid in an 18-year-old boy. Despite the extensive damage to the wrist joint, the functional results of open reduction and suture of intercarpal ligaments have been satisfactory, without carpal instability and degenerative osteoarthritis.
Posterior Interosseous Nerve Palsy
Authors: SUEMATSU N. , HIRAYAMA T.
Published: November 2005

Eleven patients with non-traumatic paralysis of posterior interosseous innervated muscles were divided into three types, and the association between the type of paralysis and sites of compression was investigated. Type 1 (drop finger and thumb) showed a simultaneous compression of the recurrent branch and the descending branch at the entrance point and within the supinator. Type 2 (drop fingers) had compression of the recurrent branch alone, and Type 3 (drop thumb) had compression of the descending branch alone. The exit point from the supinator is considered to be the site of compression in Types 2 and 3.
Ulnar Nerve Laceration as a Result of Elbow Arthroscopy
Authors: HAHN M. , GROSSMAN J. A. I.
Published: November 2005

We report a case of an ulnar laceration during elbow arthroscopy in a 31-year-old man.
Median Nerve Contusion during Endoscopic Carpal Tunnel Release
Authors: DHEANSA B. S. , BELCHER H. J. C. R.
Published: November 2005

Median nerve contusion occurred in two patients treated by endoscopic carpal tunnel release. We discuss the possible cause of this complication and how to avoid it.
Von Willebrand’s Disease presenting as Acute Carpal Tunnel Syndrome
Authors: PARTHENIS D. G. , KARAGKEVREKIS C. B. , WALDRAM M. A.
Published: November 2005

We describe a patient who developed acute carpal tunnel syndrome due to spontaneous bleeding without a history of injury. Immediate decompression relieved the symptoms. Further haematological investigations revealed that the patient was suffering from von Willebrand’s disease.
Entrapment of the Palmar Cutaneous Branch of the Median Nerve
Authors: DE SMET L.
Published: November 2005

We report a case of anterior wrist pain and numbness of the palm of the hand caused by compression of the palmar cutaneous branch of the median nerve by an occult synovial cyst.
Intraneural Lipofibroma of the Median Nerve
Authors: CAMILLERI I. G. , MILNER R. H.
Published: November 2005

Intraneural lipofibroma of the median nerve is rare. We present three cases of this condition and discuss the surgical management. Open biopsy and carpal tunnel release are usually required.
Intraneural Ganglion of the Brachial Plexus
Authors: NAKAMICHI K. , TACHIBANA S.
Published: November 2005

We report a case of an intraneural ganglion of the brachial plexus. Excision relieved the symptoms.
Avulsion of the Flexor Digitorum Profundus Tendon Associated with a Chondroma of the Distal Phalanx
Authors: CANOVAS F. , NICOLAU F. , BONNEL F.
Published: November 2005

An avulsion of the profundus tendon associated with a chondroma of the distal phalanx is presented. The injury occurred during housework and the tendon avulsion can be explained by a weakness of the profundus tendon insertion.
An Unusual Variant of the Levator Claviculae Muscle Encountered in Exploration of the Brachial Plexus
Authors: O’SULLIVAN S. T. , KAY S. P. J.
Published: November 2005

The levator claviculae muscle is a vestigal muscle which occurs in less than 2% of humans. The embryological origin of this muscle is controversial. We report a case in which an unusual variant of this muscle was encountered during exploratory surgery following a brachial plexus injury. The anatomical findings in this case suggest that this muscle may arise from either the sternocleidomastoid or trapezius muscles or from the primordial ventrolateral musculature.
Evolution on display: promoting Irish natural history and Darwinism at the Dublin Science and Art Museum
Authors: ADELMAN JULIANA
Published: November 2005

In 1890 the staff of the Dublin Natural History Museum began a comprehensive rearrangement of the collection in their care. Inspired by visits to American museums and motivated by a desire to produce a truly educational display, curators arranged the zoological collection to include cases on the history and geographical distribution of animals. These cases explicitly depicted, in words and specimens, the main arguments of Charles Darwin's On the Origin of Species. Placed at a ground-floor entrance to the museum, the cases invited the visitor to examine the remainder of the collection in terms of evolution by natural selection. The exhibit was supplemented by guidebooks and several lecture-demonstrations, which served to further reinforce its messages. Through an analysis of the exhibit's development and contents, this paper will show how these cases reflected not only the status of evolutionary thinking in Ireland, but also the curators' goals for the future development of Irish natural history.
Dissolved organic carbon and dissolved organic nitrogen export from forested watersheds in Nova Scotia: Identifying controlling factors
Authors: Aitkenhead‐Peterson J. A. , Alexander J. E. , Clair T. A.
Published: November 2005

Riverine nutrient export represents a transfer of terrestrial nutrients to lakes, estuaries and the near‐coastal zone. In this study, we constructed regional predictive models for riverine dissolved organic carbon (DOC) and organic nitrogen (DON) exports. We used a subset of 10 watersheds to construct regional empirical models of DOC and DON export, reserving two watersheds for testing the predictive ability of each model. For the subset of 10 watersheds, mean watershed soil column C:N ratio explained 75% of the variance in DOC export and 73% of the variance in DON export (p < 0.01). Organic C:N explained 63% and 71% of the variance in DOC and DON exports, respectively. There was a stronger relationship between riverine DOC:DON ratio and mineral soil C:N (R2 = 0.77 p < 0.001) than with organic C:N (R2 = 0.49 p < 0.05), suggesting that de‐coupling of DOC and DON dynamics in rivers may occur when hydrologic flow paths favor organic layers. We suggest that mean watershed soil C:N ratio is likely to be an integrator of several controls on riverine DOC export including temperature and precipitation (climatic control), soil texture and nutrient status (edaphic control), vegetative species and their associated micro‐flora (biological control) and watershed topography (topographical control). Soil C:N appears to be a useful tool for predicting variability in both DOC and DON flux at a regional scale.
Representation of vegetation and other nonerodible elements in aeolian shear stress partitioning models for predicting transport threshold
Authors: King James , Nickling William G. , Gillies John A.
Published: November 2005

The presence of nonerodible elements is well understood to be a reducing factor for soil erosion by wind, but the limits of its protection of the surface and erosion threshold prediction are complicated by the varying geometry, spatial organization, and density of the elements. The predictive capabilities of the most recent models for estimating wind driven particle fluxes are reduced because of the poor representation of the effectiveness of vegetation to reduce wind erosion. Two approaches have been taken to account for roughness effects on sediment transport thresholds. Marticorena and Bergametti (1995) in their dust emission model parameterize the effect of roughness on threshold with the assumption that there is a relationship between roughness density and the aerodynamic roughness length of a surface. Raupach et al. (1993) offer a different approach based on physical modeling of wake development behind individual roughness elements and the partition of the surface stress and the total stress over a roughened surface. A comparison between the models shows the partitioning approach to be a good framework to explain the effect of roughness on entrainment of sediment by wind. Both models provided very good agreement for wind tunnel experiments using solid objects on a nonerodible surface. However, the Marticorena and Bergametti (1995) approach displays a scaling dependency when the difference between the roughness length of the surface and the overall roughness length is too great, while the Raupach et al. (1993) model's predictions perform better owing to the incorporation of the roughness geometry and the alterations to the flow they can cause.
Space‐time optimization of groundwater quality sampling networks
Authors: Herrera Graciela S. , Pinder George F.
Published: November 2005

A method is herein proposed and demonstrated for the space‐time optimization of monitoring networks for groundwater quality. The objective is to provide a minimum cost design algorithm that will assist in determining where and when to sample existing wells dedicated to defining, through periodic sampling, the behavior of groundwater contaminants. The method has three characteristics: (1) The combined spatial and temporal redundancy of the sampling network is considered by using a Kalman filter coupled with a stochastic transport model in which velocity and dispersion are spatially correlated random fields. (2) The sampling network is optimized using an enumerative method that minimizes a function of the estimate variance. (3) A real‐time update of the estimate is obtained using again the Kalman filter. The synthetic examples presented show that for a contaminant plume in motion this method can obtain cost‐effective sampling networks.
Liquid fragmentation and intermittent flow regimes in unsaturated fractured media
Authors: Ghezzehei Teamrat A. , Or Dani
Published: November 2005

Flow processes in unsaturated fractures considerably differ from flow in rock matrix because of the dominance of gravitational forces, accentuated by variations in fracture geometry. This gives rise to liquid fragmentation, fingering, and intermittent flow regimes that are not amenable to standard continuum representation. We develop an alternative modeling framework to describe the onset of liquid fragmentation and subsequent flow behavior of discrete liquid clusters. The transition from a slowly growing anchored liquid element to a finger‐forming mobile liquid element is estimated from the force balance between retarding capillary forces dominated by contact angle hysteresis and suspended liquid weight. A model for liquid fragmentation within the fracture plane (smooth and parallel walled fractures) for given a steady input flux and aperture size is developed and tested. Predictions of sizes and detachment intervals of liquid elements are in good agreement with experimental results. The results show that the mass of detached liquid element is only weakly related to flow rate but increases with fracture aperture size. Periodic discharge similar to that experimentally observed is a result of the interplay between capillary, viscous, and gravitational forces. We show that the presence of even a few irregularities in a fracture plane may induce complicated flux patterns downstream. Similar erratic fluxes are observed in studies involving gravity‐driven unsaturated flow.
Estimation of global river transport of sediments and associated particulate C, N, and P
Authors: Beusen A. H. W. , Dekkers A. L. M. , Bouwman A. F. , Ludwig W. , Harrison J.
Published: November 2005

This paper presents a multiple linear regression model developed for describing global river export of sediments (suspended solids, TSS) to coastal seas, and approaches for estimating organic carbon, nitrogen, and phosphorous transported as particulate matter (POC, PN, and PP) associated with sediments. The model, with river‐basin spatial scale and a 1‐year temporal scale, is based on five factors with a significant influence on TSS yields (the extent of marginal grassland and wetland rice, Fournier precipitation, Fournier slope, and lithology), and accounts for sediment trapping in reservoirs. The model generates predictions within a factor of 4 for 80% of the 124 rivers in the data set. It is a robust model which was cross‐validated by using training and validation sets of data, and validated against independent data. In addition, Monte Carlo simulations were used to deal with uncertainties in the model coefficients for the five model factors. The global river export of TSS calculated thus is 19 Pg yr−1 with a 95% confidence interval of 11–27 Pg yr−1 when accounting for sediment trapping in regulated rivers. Associated POC, PN, and PP export is 197 Tg yr−1 (as C), 30 Tg yr−1 (N), and 9 Tg yr−1 (P), respectively. The global sediment trapping included in these estimates is 13%. Most particulate nutrients are transported by rivers to the Pacific (∼37% of global particulate nutrient export), Atlantic (28–29%), and Indian (∼20%) oceans, and the major source regions are Asia (∼50% of global particulate nutrient export), South America (∼20%), and Africa (12%).
Steady plumes produced by downwellings in Earth‐like vigor spherical whole mantle convection models
Authors: Davies J. Huw
Published: November 2005

If mantle thermal upwellings (plumes) are the cause of volcanic “hot spots,” then observations suggest that plumes are relatively fixed with nonuniform distribution and limited lifetimes. To date, fixity of upwellings has only been shown in models of convection at either low‐vigor or with layering, though studies where the lower mantle has high viscosity do frequently show upwellings with much lower drift velocities than the surface velocity. Since more vigorous convection traditionally shows more time dependence, fixity of upwellings has not been expected for nonlayered convection at Earth‐like vigor; rather, we might expect slow but increasing drift velocities. I have undertaken numerical models of whole mantle convection in three‐dimensional spherical geometry at approaching Earth‐like vigor. Surprisingly, these simulations show prominent steady, virtually fixed, plumes arising from self‐organization controlled by the smaller but numerous cold downwellings. If downwelling (subduction) dominates Earth's interior dynamics, then this work suggests that plume fixity need not require layering. The regular spacing and permanence of model upwellings contrast with observations of hot spots though. In these models, which do not simulate plates, the fixity and regular spacing result from the freedom of downwellings to occur everywhere except where plumes reach the surface. I suggest that on Earth this feedback is weakened by the presence of plates but that whole mantle thermal convection can still produce relatively fixed plumes, though we might expect them to be weaker, more mobile, and transient.
Effects of atmospheric teleconnections on seasonal precipitation in mountainous regions of the southwestern U.S.: A case study in northern New Mexico
Authors: Guan Huade , Vivoni Enrique R. , Wilson John L.
Published: November 2005

This study uses instrument records and geostatistical modeling to examine hydrologically important temporal and spatial patterns of seasonal precipitation associated with the El Niño‐Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO) in a mountainous region of northern New Mexico. PDO is the more dominant factor, compared to ENSO, with a larger influence on winter and spring precipitation (wetter for high PDO, drier for low PDO). Extreme ENSO effects are not significant during the high PDO years, but during low PDO years El Niño strongly dampens winter and spring precipitation anomalies. Elevation modulates ENSO and PDO effects on winter anomalies, but does not seem to for other seasons. For a wetter‐than‐normal winter, the anomalies are larger at higher elevations, and are positive. For a drier‐than‐normal winter, the anomalies are larger at lower elevations, and are negative. For neutral ENSO, summer precipitation is predictable but spatially variable, indicating different local climates. High‐resolution mapping brings out hydrologically important patterns of precipitation anomalies that would otherwise be blurred by spatial averaging.
THEMIS VIS and IR observations of a high‐altitude Martian dust devil
Authors: Cushing Glen E. , Titus Timothy N. , Christensen Philip R.
Published: November 2005

The Mars Odyssey Thermal Emission Imaging System (THEMIS) imaged a Martian dust devil in both visible and thermal‐infrared wavelengths on January 30, 2004. We believe this is the first documented infrared observation of an extraterrestrial dust devil, and the highest to be directly observed at more than 16 kilometers above the equatorial geoid of Mars. This dust devil measured over 700 meters in height and 375 meters across, and the strongest infrared signature was given by atmospheric dust absorption in the 9‐micron range (THEMIS IR band 5). In addition to having formed in the extremely low‐pressure environment of about 1 millibar, this dust devil is of particular interest because it was observed at 16:06 local time. This is an unusually late time of day to find dust devils on Mars, during a period when rapid surface cooling typically reduces the boundary‐layer turbulence necessary to form these convective vortices. Understanding the mechanisms for dust‐devil formation under such extreme circumstances will help to constrain theories of atmospheric dynamics, and of dust lifting and transport mechanisms on Mars.
Atmospheric hydroperoxides in West Antarctica: Links to stratospheric ozone and atmospheric oxidation capacity
Authors: Frey Markus M. , Stewart Richard W. , McConnell Joseph R. , Bales Roger C.
Published: November 2005

The troposphere above the West Antarctic Ice Sheet (WAIS) was sampled for hydroperoxides at 21 locations during 2‐month‐long summer traverses from 2000 to 2002, as part of the U.S. International Trans‐Antarctic Scientific Expedition (US ITASE). First‐time quantitative measurements using a high‐performance liquid chromatography method showed that methylhydroperoxide (MHP) is the only important organic hydroperoxide occurring in the Antarctic troposphere and that it is found at levels 10 times those previously predicted by photochemical models. During three field seasons, means and standard deviations for hydrogen peroxide (H2O2) were 321 ± 158 pptv, 650 ± 176 pptv, and 330 ± 147 pptv. While MHP was detected but not quantified in December 2000, levels in summer 2001 and 2002 were 317 ± 128 pptv and 304 ± 172 pptv. Results from firn air experiments and diurnal variability of the two species showed that atmospheric H2O2 is significantly impacted by a physical snow pack source between 76° and 90°S, whereas MHP is not. We show strong evidence of a negative correlation between stratospheric ozone and H2O2 at the surface. Between 27 November and 12 December in 2001, when ozone column densities dropped below 220 Dobson units (DU) (means in 2000 and 2001 were 318 DU and 334 DU, respectively), H2O2 was 1.7 times that observed in the same period in 2000 and 2002, while MHP was only 80% of the levels encountered in 2002. Photochemical box model runs match MHP observations only when the production rate from CH3O2 + HO2 was increased to the upper limit of its estimated range of uncertainty. Model results suggest that NO and OH levels on WAIS are closer to coastal values, while Antarctic Plateau levels are higher, confirming that region to be a highly oxidizing environment. The modeled sensitivity of H2O2 and particularly MHP to NO offers the potential to use atmospheric hydroperoxides to constrain the NO background and thus estimate the past oxidation capacity of the remote atmosphere using ice cores.
Gravity currents in aquatic canopies
Authors: Tanino Y. , Nepf H. M. , Kulis P. S.
Published: November 2005

A lock exchange experiment is used to investigate the propagation of gravity currents through a random array of rigid, emergent cylinders which represents a canopy of aquatic plants. As canopy drag increases, the propagating front varies from the classic profile of an unobstructed gravity current to a triangular profile. Unlike the unobstructed lock exchange, the gravity current in the canopy decelerates with time as the front lengthens. Two drag‐dominated regimes associated with linear and nonlinear drag laws are identified. The theoretical expression for toe velocity is supported by observed values. Empirical criteria are developed to predict the current regime from the cylinder Reynolds number and the array density.
Experimental Estimates of the Constants Relating Signal Change to Contrast Concentration for Cerebral Blood Volume by T2* MRI
Authors: Newman George C , Hospod Frank E , Patlak Clifford S , Fain Sean E , Pulfer Kari A , Cook Thomas D , O'Sullivan Finbarr
Published: November 2005

Estimates of cerebral blood volume (CBV) obtained from dynamic contrast T2* -weighted magnetic resonance imaging (MRI) tend to be significantly higher than values obtained by other methods. This may relate to the common assumption that the proportionality constants relating signal change to contrast concentration are equal in tissue and artery. To test this hypothesis and provide estimates for the ratio of those proportionality constants, the authors compared measurements of CBV by both MRI and computed tomography (CT) scans in nine healthy volunteers obtained using identical kinetic paradigms for the two imaging modalities. Both boluses and infusions of contrast were studied. Measurements were made in nine anatomic regions of interest of the cerebral hemispheres bilaterally. Cerebral blood volume values obtained by CT were generally lower than those obtained by MRI, especially in the cerebral cortex. As a result, the calculated values of the ratios of proportionality constants relating signal change to concentration in tissue and artery after bolus injections were significantly less than 1 in cortex (0.69) and white matter (0.76), although not in deep gray matter structures (0.87). Values of the ratios based on infusion measurements were closer to 1. In addition, CBV measurement errors with bolus MRI were significantly larger than those observed with infusion MRI or by CT. The reasons that the constants differ from 1 and for the larger variance of bolus MRI are discussed in terms of the T2* signal mechanisms. These studies help define the magnitude by which CBV is overestimated with typical T2*-weighted perfusion imaging. Infusion measurements of CBV can reduce the variance intrinsic to T2* MRI and lessen the likelihood of type II error.
Solid solutions Ne–nD2. Diagram of phase equilibrium
Authors: Belan V. G. , Gal’tsov N. N. , Prokhvatilov A. I. , Strzhemechnyĭ M. A.
Published: November 2005

X-Ray investigations of vacuum condensates of the binary mixtures Ne–nD2 at temperatures from 6 K to the melting point of the solutions are performed. A diagram of phase equilibrium of the liquid and solid mixtures is proposed on the basis of the experimentally obtained and published data on the phase composition and mutual solubility of the components. The isotopic effect in the mutual solubility of the components is determined. A long-lived but metastable hexagonal phase is found, and the conditions for the formation and decomposition of this phase are determined.
Diffusion description of the kinetics of isotopic phase separation of He3–4He solid solutions
Authors: Grigor’ev V. N. , Degtyarev I. A. , Sokolov S. S.
Published: November 2005

The process of the separation of solid solutions of helium isotopes is examined using a diffusion approach with boundary conditions prescribed on the boundary of the inclusion of a new phase, the position of the boundary being a function of time. The diffusion processes occurring simultaneously outside and inside an inclusion are taken into account. The time dependence of the pressure is calculated on the basis of the time dependences of the concentration of the diffusing substance. A theoretical calculation using existing experimental data is performed.
Enhancement of superconductivity in tin films of different widths by an external electromagnetic field
Authors: Dmitriev V. M. , Zolochevskiĭ I. V. , Salenkova T. V. , Khristenko E. V.
Published: November 2005

The current-voltage characteristics of high-quality thin tin films, ranging in width from 7 to 50 μm, irradiated by microwave radiation are investigated. The behavior of the critical current Ic and of the maximum current Im for the existence of a stationary flow of the characteristic vortices of the transport current (formation current of the first phase-slip line) is analyzed. The regimes of enhancement and suppression of the currents Ic and Im by a microwave field are studied and analyzed. The criteria for separating films into narrow and wide are established. It is shown that the superconductivity enhancement effect is a general effect and is observed for uniform (narrow films) and nonuniform (wide films) distributions of the superconducting current over the film width.
Evolution of the spin state of a 3d ion in a pyramidal complex
Authors: Zhitlukhina E. S. , Lamonova K. V. , Orel S. M. , Pashkevich Yu. G.
Published: November 2005

The evolution of the spin state of a metallic 3d ion in a pyramidal MeO5 environment is studied. Ions of metals with 3d6 (Fe2+,Co3+) and 3d4 configurations (Mn3+,Cr2+) are studied. The change in the spin state of the metal ion from S=0 to S=1 and S=2 with a variation of the effective charge Zeff of the metal ion and the displacements of the oxygen ions is investigated. The stability of the spin state as a function of the magnitude and symmetry of the displacements of the ligands is checked. Breathing-mode distortions, displacements of the 3d ion along the Z axis, Jahn-Teller distortions of the basal plane of the pyramid, and fluting distortions of the plane of the pyramid are studied. It is shown that different types of distortions produce different behaviors of the terms corresponding to a change in the spin states of all three types. It is found that the spin state of the coordination complex MeO5 with the 3d4 configuration of the metal ion is most sensitive to breathing-mode distortions and Jahn-Teller type distortions stabilize the state with spin S=1 for the 3d6 configuration.
Kinetics of homogeneous crystallization of nitrogen according to electron diffraction data for free clusters
Authors: Danil’chenko A. G. , Kovalenko S. I. , Samovarov V. N.
Published: November 2005

An electron diffraction investigation of the structure of free neon clusters (N2)n¯ is performed in the average-size range 102⩽n¯⩽105 molecules/cluster. The first cluster beams of nitrogen consisting of monostructural aggregations with hexagonal close packing of the molecules are obtained. A sequence of structural transformations resulting in the formation of a high-temperature β phase of nitrogen in bulk samples with homogeneous nucleation is proposed on the basis of an analysis of the results obtained.