bluuebunny/crossref_metadata_2025_split huggingface dataset:
Correlations between seismic parameters, EM parameters, and petrophysical/petrological properties for sandstone and carbonate at low water saturations
Authors: Koesoemadinata Adam P. , McMechan George A. 
Published: May 2003

Empirical relations are found between measured petrophysical/petrologic, seismic, and electrical properties of sandstone and carbonate samples by least‐squares fitting at room pressure and ambient saturation. The measured parameters include porosity (φ), fluid permeability (k), clay content (C), grain density (ρg), bulk density (ρb), P‐wave velocity (Vp), electrical conductivity (σ), and dielectric constant (κ). The samples are from reservoir analog sites in the Ferron Sandstone in central Utah and the Ellenburger carbonate in central Texas. Crossplots and regression analysis are done separately for the sandstone and the carbonate samples. For the sandstone samples, predictions with correlation coefficients (R2) greater than 0.75 include ρb from φ, ln k from φ and C, κ from ln k and φ, κ from ρb and C, and κ from ln k. Predictions with 0.65 < R2 < 0.75 include κ from Vp and ρb, κ from Vp and φ, Vp from ln k and C, κ from ln φ, and κ from ρb. In general, σ is difficult to predict, with the best R2(0.48) obtained in a prediction of σ from ln k. Relationships for the carbonate samples are generally less reliable, which is attributed to a complex history of multiple phases of karsting and burial. The largest R2 values obtained are 0.67 for prediction of σ from κ, and 0.36 for prediction of σ from ρg. All the other R2 values are ≤0.19. Both the sandstone and the carbonate data show σ‐φ; relations with negative coefficients, rather than positive as predicted by Archie's law, because of the very low water saturations. In the sandstone, the water connectivity is reduced with increasing grain surface area (with increasing φ and k), so σ decreases. In the carbonate, σ correlates with the degree of dolomitization, and the water content is too low to contribute to σ.
Enhancing the resolving power of least‐squares inversion with active constraint balancing
Authors: Yi Myeong‐Jong , Kim Jung‐Ho , Chung Seung‐Hwan 
Published: May 2003

Most geophysical inverse problems are solved using least‐squares inversion schemes with damping or smoothness constraints to improve stability and convergence rate. Since the Lagrangian multiplier controls resolution and stability of the inverse problem, we always want to use the optimum multiplier, which is not easy to get and is usually obtained by experience or a time‐consuming optimization process. We present a new regularization approach, in which the Lagrangian multiplier is set as a spatial variable at each parameterized block and automatically determined via the parameter resolution matrix and spread function analysis. For highly resolvable parameters, a small value of the Lagrangian multiplier is assigned, and vice versa. This approach, named “active constraint balancing” (ACB), tries to balance the constraints of the least‐squares inversion according to sensitivity for a given problem so that it enhances the resolution as well as the stability of the inversion process. We demonstrate the performance of the ACB by applying it to a two‐dimensional resistivity tomography problem, which results in a remarkable enhancement of the spatial resolution. Enhancement of the resolution is also verified in the application of resistivity tomography to a field data set acquired at a tunnel construction site.
Gaussian envelope for 3D geomagnetic data inversion
Authors: Tontini Fabio Caratori , Faggioni Osvaldo , Beverini Nicolò , Carmisciano Cosmo 
Published: May 2003

We describe an inversion method for 3D geomagnetic data based on approximation of the source distribution by means of positive constrained Gaussian functions. In this way, smoothness and positivity are automatically imposed on the source without any subjective input from the user apart from selecting the number of functions to use. The algorithm has been tested with synthetic data in order to resolve sources at very different depths, using data from one measurement plane only.The forward modeling is based on prismatic cell parameterization, but the algebraic nonuniqueness is reduced because a relationship among the cells, expressed by the Gaussian envelope, is assumed to describe the spatial variation of the source distribution.We assume that there is no remanent magnetization and that the magnetic data are produced by induced magnetization only, neglecting any demagnetization effects. The algorithm proceeds by minimization of a χ2misfit function between real and predicted data using a nonlinear Levenberg‐Marquardt iteration scheme, easily implemented on a desktop PC, without any additional regularization. We demonstrate the robustness and utility of the method using synthetic data corrupted by pseudorandom generated noise and a real field data set.
Identifying, removing, and imaging P‐S conversions at salt‐sediment interfaces
Authors: Lu Richard S. , Willen Dennis E. , Watson Ian A. 
Published: May 2003

The large velocity contrast between salt and the surrounding sediments generates strong conversions between P‐ and S‐wave energy. The resulting converted events can be noise on P‐wave migrated images and should be identified and removed to facilitate interpretation. On the other hand, they can also be used to image a salt body and its adjacent sediments when the P‐wave image is inadequate. The converted waves with smaller reflection and transmission angles and much larger critical angles generate substantially different illumination than does the P‐wave. In areas where time migration is valid, the ratio between salt thickness in time and the time interval between the P‐wave and the converted‐wave salt base on a time‐migrated image is about 2.6 or 1.3, depending upon whether the seismic wave propagates along one or both of the downgoing and upcoming raypaths in salt as the S‐wave, respectively. These ratios can be used together with forward seismic modeling and 2D prestack depth migration to identify the converted‐wave base‐of‐salt (BOS) events in time and depth and to correctly interpret the subsalt sediments. It is possible to mute converted‐wave events from prestack traces according to their computed arrival times. Prestack depth migration of the muted data extends the updip continuation of subsalt sedimentary beds, and improves the salt–sediment terminations in the P‐wave image. Prestack and poststack depth‐migrated examples illustrate that the P‐wave and the three modes of converted waves preferentially image different parts of the base of salt. In some areas, the P‐wave BOS can be very weak, obscured by noise, or completely absent. Converted‐wave imaging complements P‐wave imaging in delineating the BOS for velocity model building.
Cancellation of multiple harmonic noise series in geophysical records
Authors: Butler Karl E. , Russell R. Don 
Published: May 2003

We describe a procedure for the simultaneous estimation of multiple stationary sinusoidal contaminants in a time series and demonstrate its application to the cancellation of powerline noise in seismic and seismoelectric records. An estimate of the noise in each record is obtained by seeking a linear combination of sinusoids that are harmonics of one or more fundamental frequencies; this combination must fit the data in a least‐squares sense. The algorithm accommodates estimation windows of arbitrary length, including windows shorter than one fundamental period, without cross‐contamination between harmonic estimates.Provision is made for refining the fundamental frequencies, for which small errors (e.g., 0.01 Hz in 60 Hz) can result in significant residual noise near the ends of the record (beating). Our strategy is novel in that it uses all specified harmonics and iteratively searches frequency space for a best fit using numerical derivatives. This determination is very robust for at least two fundamentals (the limit of our investigation) and often converges rapidly to three or four decimal places.Cancellation of harmonic noise has been essential in our research to uncover seismoelectric signals that are often completely masked by powerline noise. We expect this procedure will be useful in other geophysical methods—especially exploration seismology, for which powerline contamination is a recognized problem.
Adaptive decomposition of multicomponent ocean‐bottom seismic data into downgoing and upgoing P‐ and S‐waves
Authors: Schalkwijk K. M. , Wapenaar C. P. A. , Verschuur D. J. 
Published: May 2003

With wavefield decomposition, the recorded wavefield at a certain depth level can be separated into upgoing and downgoing wavefields as well as into P‐ and S‐waves. The medium parameters at the considered depth level (e.g., just below the ocean‐bottom) need to be known in order to be able to do a decomposition. In general, these parameters are unknown and, in addition, measurement‐related issues, such as geophone coupling and crosstalk between the different components, need to be dealt with. In order to apply decomposition to field data, an adaptive five‐stage decomposition scheme was developed in which these issues are addressed. In this study, the adaptive decomposition scheme is tested on a data example with a relatively shallow water depth (∼120 m), consisting recordings from of a full line of ocean‐bottom receivers. Although some of the individual stages in the decomposition scheme are more difficult to apply because of stronger interference between events compared to data acquired over deeper water, the end result is satisfying. Also, a good decomposition result is obtained for the S‐waves. The extension of the decomposition scheme to a complete line of ocean‐bottom cable data consists of a repeated application of the procedure for each receiver. The resulting decomposed upgoing P‐ and S‐wavefields are processed, yielding poststack time migrated images of the subsurface. Comparison with the images obtained from the original (i.e., not decomposed) measurements shows that wavefield decomposition just below the ocean bottom leads to a strong attenuation of multiply reflected events at the sea surface and better event definition in both P‐ and S‐wave sections. Other decomposition effects like improved angle‐dependent amplitudes cannot be evaluated in this way.
Tapering off long-term benzodiazepine use with or without group cognitive-behavioural therapy: three-condition, randomised controlled trial
Authors: Voshaar Richard C. Oude , Gorgels Wim J. M. J. , Mol Audrey J. J. , Van Balkom Anton J. L. M. , Van De Lisdonk Eloy H. , Breteler Marinus H. M. , Van Den Hoogen J. M. , Zitman Frans G. 
Published: June 2003

BackgroundBenzodiazepine withdrawal programmes have never been experimentally compared with a nonintervention control condition.AimsTo evaluate the efficacy and feasibility of tapering off long-term benzodiazepine use in general practice, and to evaluate the value of additional group cognitive–behavioural therapy (CBT).MethodA 3-month randomised, controlled trial was conducted in which 180 people attempting to discontinue long-term benzodiazepine use were assigned to tapering off plus group CBT, tapering off alone or usual care.ResultsTapering off led to a significantly higher proportion of successful discontinuations than usual care (62% v. 21%). Adding group CBT did not increase the success rate (58% v. 62%). Neither successful discontinuation nor intervention type affected psychological functioning. Both tapering strategies showed good feasibility in general practice.ConclusionsTapering off is a feasible and effective way of discontinuing long-term benzodiazepine use in general practice. The addition of group CBT is of limited value.
Continuation of clozapine treatment: practice makes perfect
Authors: Whiskey Eromona , Wykes Til , Duncan-McConnell Denise , Haworth Elke , Walsh Nick , Hastilow Sarah 
Published: June 2003

Aims and MethodThe study aimed to identify the predictors of drop-out from clozapine treatment by examining the demographic and clinical characteristics of patients registered on clozapine within a 6-month period in one NHS Trust.ResultsDuring the study period, 54 patients were registered and began clozapine treatment and 31% had discontinued within 6 months. Two people died and the remainder discontinued because of non-compliance or side-effects, including neutropenia. Two factors were predictive: the age of the patient (older patients were more likely to discontinue) and the hospital where the initial registration was made.Clinical ImplicationsNeither ethnicity, previous registration nor the individual prescriber are a bar to successful persistence with clozapine. However, one set of hospitals with a history of evidence-based practice and high clozapine prescribing was more successful in retaining patients on maintenance treatment. Although specific data are needed to identify more subtle contributing factors to continuation, it is clear that there is scope for improving the rate of persistence with clozapine treatment.
Computed tomography in suppurative ear disease: does it influence management?
Authors: Banerjee A. , Flood L. M. , Yates P. , Clifford K. 
Published: June 2003

The value of high resolution computerized tomography (CT) prior to routine mastoid surgery for cholesteatoma remains controversial. Doubts about sensitivity and specificity, in detecting the extent of underlying pathology and in predicting asymptomatic complications, prevent widespread adoption.This retrospective study looks at the influence of pre-operative scanning on the surgical management of chronic suppurative otitis media over an 18-month period. The radiological findings determined the choice of surgical approach, but contributed less to the decision to operate and the prediction of potential hazards. CT is of most value when the otologist can be flexible in surgical technique, tailoring it to imaging findings.
Intratympanic gentamicin for Ménière’s disease; a survey of current UK practice
Authors: Obholzer R. J. , Wareing M. J. 
Published: June 2003

Intratympanic gentamicin is increasingly used in the treatment of Ménière’s disease. Many protocols have been published for its use, but there is little difference in outcome between them. The goal of the study was therefore to assess current UK practice in the use of intratympanic gentamicin.A postal and e-mail survey of consultant ENT surgeons in the UK was conducted. Of 34 consultants who regularly used intratympanic gentamicin, 21 used a protocol based upon a single intratympanic dose of gentamicin via a needle through the tympanic membrane and repeated after at least a week. The remaining 13 used either a regime of more frequent administration or attempted a more complicated route of delivery in an effort to improve reliability and selectivity of action.In the absence of evidence demonstrating benefit from regimens of increased complexity the majority of consultants are using the simplest possible protocol.
A middle-ear simulator for practicing prosthesis placement for otosclerosis surgery using ward-based materials
Authors: Owa A. O. , Gbejuade H. O. , Giddings C. 
Published: June 2003

Complications following stapedectomy are the most common cause of litigation involving otological cases in the USA. Manipulation and placement of the prosthesis during a stapedectomy may have a profound effect on the final hearing results. Concerns have been raised over the reduced number of cases, training of residents, and the maintenance of the necessary skills to achieve consistently good results.Temporal bone dissection is an important adjunct to developing the required skills to perform stapedectomies. However the reduced availability of specimens limits their use for teaching or practising the procedure.In order to circumvent these problems an inexpensive and easily constructed middle-ear simulator has been developed based on materials readily available in any ENT ward. It is believed that this might help trainees develop the necessary skills to master the procedure.
Cefepime versus Ceftazidime as Empiric Therapy for Fever in Neutropenic Patients with Cancer
Authors: Chandrasekar Pranatharthi H , Arnow Paul M 
Published: June 2003

OBJECTIVE: To compare the efficacies of cefepime and ceftazidime as empiric therapy during the management of fever in cancer patients with chemotherapy-induced neutropenia. METHODS: A prospective, double-blind, randomized study of cefepime 2 g every eight hours and ceftazidime 2 g every eight hours was performed in 276 adult neutropenic (absolute neutrophil count <500/mm3) cancer patients with fever. RESULTS: Median duration of neutropenia was five days. Sixty-one percent (n = 188) of the patients were evaluable. Treatment was successful in 57% (58/101) of cefepime-treated patients and 60% (52/87) of ceftazidime-treated patients (95% CI −18 to 12; p = 0.77). Bacteremic clearance occurred in 71% (12/17) of cefepime-treated patients and 40% (6/15) of ceftazidime-treated patients (p = 0.3). Both drugs were well tolerated. CONCLUSIONS: Cefepime appears to be as effective as ceftazidime in the initial treatment of febrile episodes in adult cancer patients with chemotherapy-associated neutropenia of modest duration.
Evaluation of Outcomes in Converting from Intravenous Ondansetron to Oral Granisetron: An Observational Study
Authors: McCune Jeannine S , Oertel Maryann D , Pfeifer Dennis , Houston Shelly A , Bingham Andrea , Sawyer William T , Lindley Celeste M 
Published: June 2003

OBJECTIVE: To describe a systematic evaluation of the outcomes associated with revising institutional guidelines for the prevention of acute chemotherapy-induced nausea and vomiting (CINV) to promote cost-effective use of the serotonin (5-HT3) antagonists. METHODS: The 5-HT3 antagonist of choice in the antiemetic guidelines was revised from intravenous ondansetron to oral granisetron in August 1995. Patient assessments were conducted immediately prior to (Period 1) and after (Period 2) guideline revision using validated questionnaires. The effectiveness of the two 5-HT3 antagonists were compared and reported to the prescribing oncologists. Outcomes were assessed one year after guideline revision (Period 3) using identical methods. RESULTS: No difference was found in the rate of total control (no emesis, no nausea) between patients receiving oral granisetron (60%) and intravenous ondansetron (56%) (p = 0.408, Period 1 vs. 2). Nausea severity, the number of emesis episodes, and use of rescue antiemetics were also equivalent. Prescriber compliance with using the 5-HT3 antagonist of choice and dose increased from 48% to 61% following adoption of oral granisetron. By Period 3, compliance increased to 78%, and satisfactory control of acute CINV was again documented. The costs for prevention of acute CINV decreased from $107 in Period 1 (intravenous ondansetron only) to $65 in Period 3 (oral granisetron). CONCLUSIONS: Outcomes associated with use of oral granisetron and intravenous ondansetron were equivalent in this patient population. Guideline revision and outcome documentation by the oncology pharmacists resulted in increased compliance with institution guidelines and a 40% cost savings.
Hypothyroidism and Depression: A Therapeutic Challenge
Authors: Rack Sarah Kotchen , Makela Eugene H 
Published: June 2003

OBJECTIVE: To describe a patient with longstanding depression and hypothyroidism who had marked mood improvement only after triiodothyronine (T3) was added to her thyroxine (T4) replacement therapy. CASE SUMMARY: A 50-year-old white woman had a long history of depression and documented hypothyroidism since 1991. Despite treatment with T4 with dosages up to 0.3 mg/d, she continued to be depressed, have symptoms of hypothyroidism, and have a persistently elevated thyroid-stimulating hormone concentration. Addition of a low dose of T3 to her regimen resulted in significant mood improvement. DISCUSSION: The relationship between hypothyroidism and depression is well known. It is possible that this patient's long history of depression may have been a consequence of inadequately treated hypothyroidism, due either to poor patient compliance or resistance to T4. Nevertheless, her depression responded to addition of a low dose of T3 to her regimen. This case emphasizes the importance of screening depressed patients for hypothyroidism. Her clinical course also suggests that depression related to hypothyroidism may be more responsive to a regimen that includes T3 rather than to replacement with T4 alone. This is consistent with the observation that T3 is superior to T4 as adjuvant therapy in the treatment of unipolar depression. CONCLUSIONS: Depressed patients should be screened for hypothyroidism. In hypothyroid patients, depression may be more responsive to a replacement regimen that includes T3 rather than T4 alone. Therefore, inclusion of T3 in the treatment regimen may be warranted after adequate trial with T4 alone.
Treatment of Affective Disorder and Obesity with Topiramate
Authors: Teter Christian J , Early John J , Gibbs Carol M 
Published: June 2003

OBJECTIVE: To report a case of weight loss and mood stabilization in a patient being treated with the antiepileptic drug topiramate. CASE SUMMARY: A 37-year-old obese white woman with affective instability and obesity was being treated with adjunctive topiramate therapy. The patient lost 10 kg over 10 weeks of treatment with topiramate and improved clinically, as evidenced by a reduction in the number of × that she had to be admitted to a management unit for constant observation, and a decrease in the number of × that mechanical restraints or medication interventions were required for aggressive outbursts. Furthermore, the patient successfully completed two home visits while receiving topiramate therapy and was out of the hospital on her third home visit at the time of this writing. DISCUSSION: This case further strengthens previous reports that topiramate may be useful in treating affective disorders as well as inducing weight loss in a patient population in which weight gain is common. The patient discussed in this case report had no acute illnesses or changes in health status, no changes in diet, and no changes in her medications that could have accounted for the sudden weight loss. In addition, the patient's behavior did not improve until topiramate was added as adjunctive therapy of valproic acid, citalopram, and chlorpromazine during an adequate trial period. CONCLUSIONS: Controlled studies need to be performed to evaluate the use of topiramate in the psychiatric population and, in particular, the benefits of topiramate therapy in psychiatric patients with an additional diagnosis of obesity.
Toxic Metronidazole-Induced MRI Changes
Authors: Horlen Cheryl K , Seifert Charles F , Malouf Cathy S 
Published: June 2003

OBJECTIVE: To report a case of changes documented by magnetic resonance imaging (MRI) of the head probably due to accumulation of metronidazole in a patient with liver dysfunction. CASE SUMMARY: A 34-year-old Hispanic man with cirrhosis and hepatitis C being treated with metronidazole for Bacteroides fragilis meningitis and bacteremia developed ataxia, disorientation, and peripheral neuropathy. An MRI at the time meningitis was diagnosed was negative. After the patient received >60 g of metronidazole, an MRI revealed increased signal intensity below, behind, and lateral to the fourth ventricle. Concomitant metronidazole serum concentration was toxic at 35.1 μg/mL. DISCUSSION: This is the second reported case of metronidazole-induced MRI changes. Metronidazole is known to accumulate in patients with liver dysfunction and can cause peripheral neuropathy and central nervous system (CNS) dysfunction; these effects may take up to two years to completely resolve. CONCLUSIONS: Metronidazole dosages should be reduced in patients with liver dysfunction to prevent the accumulation of metronidazole, which can lead to CNS dysfunction and peripheral neuropathy.