Biomedical subjects

Thomas M Miller

Publications and source records attributed to Thomas M Miller.

15 recordsLinked to original sources

PubMed2006

Electron attachment to MoF6, ReF6, and WF6; reaction of MoF6(-) with ReF6 and reaction of Ar+ with MoF6.

Rate constants were measured for electron attachment to MoF(6), ReF(6), and WF(6) in 133 Pa of helium gas using a flowing-afterglow Langmuir-probe apparatus. The experiment is a thorny one because the molecules tend to form oxide impurities on feedline surfaces and because of thermal decomposition of MoF(6) on surfaces as the gas temperature is increased. The electron attachment rate constant for MoF(6) is (2.3+/-0.8)x10(-9) cm(3) s(-1) at 297 K; only MoF(6) (-) is formed in the temperature range of 297-385 K. The rate constant increases with temperature up to the point where decomposition becomes apparent. Electron attachment to ReF(6) occurs with a rate constant of (2.4+/-0.8)x10(-9) cm(3) s(-1) at 297 K; only ReF(6) (-) is produced. MoF(6) (-) reacts with ReF(6) to form ReF(6) (-) on essentially every collision, showing definitively that the electron affinity of ReF(6) is greater than that of MoF(6). A rate constant of (5.0+/-1.3)x10(-10) cm(3) s(-1) was measured for this ion-molecule reaction at 304 K. The reverse reaction is not observed. The reaction of Ar(+) with MoF(6) was found to produce MoF(5) (+)+F, with a rate constant of (1.8+/-0.5)x10(-9) cm(3) s(-1). WF(6) attaches electrons so slowly at room temperature that the attachment rate was below detection level (< or =10(-12) cm(3) s(-1)). By 552 K, the attachment rate constant reaches a value of (2+/-1)x10(-10) cm(3) s(-1).

Journal Article↗

PubMed2006

Observation of dihalide elimination upon electron attachment to oxalyl chloride and oxalyl bromide, 300-550 K.

Rate coefficients have been measured for electron attachment to oxalyl chloride [ClC(O)C(O)Cl] and oxalyl bromide [BrC(O)C(O)Br] in He gas at 133 Pa pressure over the temperature range of 300-550 K. With oxalyl chloride, the major ion product of attachment is Cl2(-) at all temperatures (66% at 300 K); its importance increases slightly as temperature increases. Two other product ions formed are Cl- (18% at 300 K) and the phosgene anion CCl2O- (16% at 300 K) and appear to arise from a common mechanism. With oxalyl bromide, the Br2(-) channel represents almost half of the ion product of attachment, independent of temperature. Br- accounts for the remainder. For oxalyl chloride, the attachment rate coefficient is small [(1.8 +/- 0.5) x 10(-8) cm3 s(-1) at 300 K], and increases with temperature. The attachment rate coefficient for oxalyl bromide [(1.3 +/- 0.4) x 10(-7) cm3 s(-1) at 300 K] is nearly collisional and increases only slightly with temperature. Stable parent anions C2Cl2O2(-) and C2Br2O2(-) and adduct anions Cl- (C2Cl2O2) and Br- (C2Br3O2) were observed but are not primary attachment products. G2 and G3 theories were applied to determine geometries of products and energetics of the electron attachment and ion-molecule reactions studied. Electron attachment to both oxalyl halide molecules leads to a shorter C-C bond and longer C-Cl bond in the anions formed. Trans and gauche conformers of the neutral and anionic oxalyl halide species have similar energies and are more stable than the cis conformer, which lies 100-200 meV higher in energy. For C2Cl2O2, C2Cl2O2(-), and C2Br2O2(-), the trans conformer is the most stable conformation. The calculations are ambiguous as to the oxalyl bromide geometry (trans or gauche), the result depending on the theoretical method and basis set. The cis conformers for C2Cl2O2 and C2Br2O2 are transition states. In contrast, the cis conformers of the anionic oxalyl halide molecules are stable, lying 131 meV above trans-C2Cl2O2(-) and 179 meV above trans-C2Br2O2(-). Chien et al. [J. Phys. Chem. A 103, 7918 (1999)] and Kim et al. [J. Chem. Phys. 122, 234313 (2005)] found that the potential energy surface for rotation about the C-C bond in C2Cl2O2 is "extremely flat." Our computational data indicate that the analogous torsional surfaces for C2Br2O2, C2Cl2O2(-), and C2Br2O2(-) are similarly flat. The electron affinity of oxalyl chloride, oxalyl bromide, and phosgene were calculated to be 1.91 eV (G3), and 2.00 eV (G2), and 1.17 eV (G3), respectively.

Journal Article↗

PubMed2006

Rate constants for the reactions of CO3- and O3- with SO2 from 300 to 1440 K.

Rate constants for the reactions of CO(3) (-) and O(3) (-) with SO(2) have been measured between 300 and 1440 K in a high temperature flowing afterglow apparatus. The CO(3) (-) rate constants near to the collision rate at low temperatures and fall by about a factor of 50 with temperature until a broad minimum is reached at 900-1300 K. The highest temperature point shows the increasing rate constant. Comparison to drift tube data taken in a helium buffer shows that total energy controls the reactivity, presumably because the reaction goes through a long lived complex even at 1440 K. The reaction of O(3) (-) with SO(2) was studied up to 1400 K. The rate constant is collisional until 700 K and then decreases with increasing temperature. Rate constants measured at 1300 and 1400 K appear to show an increase, but that observation is questionable since O(3) (-) could not be made cleanly. The O(3) (-) data at 1200 K and below show that total energy controls reactivity in that range.

Journal Article↗

PubMed2006

Electron attachment to POCl3: measurement and theoretical analysis of rate constants and branching ratios as a function of gas pressure and temperature, electron temperature, and electron energy.

Two experimental techniques, electron swarm and electron beam, have been applied to the problem of electron attachment to POCl3, with results indicating that there is a competition between dissociation of the resonant POCl3-* state and collisional stabilization of the parent anion. In the electron beam experiment at zero electron energy, the fragment ion POCl2- is the dominant ion product of attachment (96%), under single-collision conditions. Small amounts (approximately 2% each) of POCl3- and Cl- were observed. POCl3- and POCl2- ion products were observed only at zero electron energy, but higher-energy resonances were recorded for POCl-, Cl-, and Cl2- ion products. In the electron swarm experiment, which was carried out in 0.4-7 Torr of He buffer gas, the parent anion branching ratio increased significantly with pressure and decreased with temperature. The electron attachment rate constant at 297 K was measured to be (2.5+/-0.6)x10(-7) cm3 s(-1), with ion products POCl2- (71%) and POCl3- (29%) in 1 Torr of He gas. The rate constant decreased as the electron temperature was increased above 1500 K. Theory is developed for (a) the unimolecular dissociation of the nascent POCl3-* and (b) a stepladder collisional stabilization mechanism using the average energy transferred per collision as a parameter. These ideas were then used to model the experimental data. The modeling showed that D0 o(Cl-POCl2-) and EA(POCl3) must be the same within +/-0.03 eV.

Journal Article↗

PubMed2005

Electron attachment and detachment, and the electron affinities of C5F5N and C5HF4N.

Rate constants have been measured for electron attachment to C5F5N (297-433 K) and to 2, 3, 5, 6-C5HF4N (303 K) using a flowing-afterglow Langmuir-probe apparatus (at a He gas pressure of 133 Pa). In both cases only the parent anion was formed in the attachment process. The attachment rate constants measured at room temperature are 1.8 +/- 0.5 X 10(-7) and 7 +/- 3 X 10(-10) cm(-3) s(-1), respectively. Rate constants were also measured for thermal electron detachment from the parent anions of these molecules. For C5F5N- detachment is negligible at room temperature, but increases to 2530 +/- 890 s(-1) at 433 K. For 2, 3, 5, 6-C5HF4N-, the detachment rate at 303 K was 520 +/- 180 s(-1). The attachment/detachment equilibrium yielded experimental electron affinities EA(C5F5N)=0.70 +/- 0.05 eV and EA(2, 3, 5, 6-C5HF4N)=0.40 +/- 0.08 eV. Electronic structure calculations were carried out for these molecules and related C5HxF5-xN using density-functional theory and the G3(MP2)//B3LYP compound method. The EAs are found to decrease by 0.25 eV, on average, with each F substitution by H. The calculated EAs are in good agreement with the present experimental results.

Journal Article↗

PubMed2005

Reactions of POxCly- ions with H and H2 from 298 to 500 K.

Rate constants and product branching ratios for POxCly- ions reacting with H and H2 were measured in a selected ion flow tube (SIFT) from 298 to 500 K. PO2Cl-, PO2Cl2-, POCl2-, and POCl3- were all unreactive with H2, having a rate constant with an upper limit of <5 x 10(-12) cm3 s(-1). PO2Cl2- did not react with H atoms either, having a similar rate constant limit of <5 x 10(-12) cm3 s(-1). The rate constants for PO2Cl-, POCl2-, and POCl3- reacting with H showed no temperature dependence over the limited range of 298-500 K and were approximately 10-20% of the collision rate constant. Cl abstraction by H to form HCl was the predominant product channel for PO2Cl-, POCl2-, and POCl3-, with a small amount of Cl- observed from POCl2- + H. Reactions of O2 and O3 with the POCl- products ions from the reaction of POCl2- + H were observed to yield predominantly PO3- and PO2-, respectively. POCl- reacted with O2 and O3 with rate constants of 8.9 +/- 1.1 x 10(-11) and 5.2 +/- 3.3 x 10(-10) cm3 s(-1), respectively. No associative electron detachment in the reactions with H atoms was observed with any of the reactant ions; however, detachment was observed with a PO- secondary product ion at high H atom concentrations. Results of new G3 theoretical calculations of optimized geometries and energies for the products observed are discussed.

Journal Article↗

PubMed2005

A primary care, multi-disciplinary disease management program for opioid-treated patients with chronic non-cancer pain and a high burden of psychiatric comorbidity.

BACKGROUND: Chronic non-cancer pain is a common problem that is often accompanied by psychiatric comorbidity and disability. The effectiveness of a multi-disciplinary pain management program was tested in a 3 month before and after trial. METHODS: Providers in an academic general medicine clinic referred patients with chronic non-cancer pain for participation in a program that combined the skills of internists, clinical pharmacists, and a psychiatrist. Patients were either receiving opioids or being considered for opioid therapy. The intervention consisted of structured clinical assessments, monthly follow-up, pain contracts, medication titration, and psychiatric consultation. Pain, mood, and function were assessed at baseline and 3 months using the Brief Pain Inventory (BPI), the Center for Epidemiological Studies-Depression Scale scale (CESD) and the Pain Disability Index (PDI). Patients were monitored for substance misuse. RESULTS: Eighty-five patients were enrolled. Mean age was 51 years, 60% were male, 78% were Caucasian, and 93% were receiving opioids. Baseline average pain was 6.5 on an 11 point scale. The average CESD score was 24.0, and the mean PDI score was 47.0. Sixty-three patients (73%) completed 3 month follow-up. Fifteen withdrew from the program after identification of substance misuse. Among those completing 3 month follow-up, the average pain score improved to 5.5 (p = 0.003). The mean PDI score improved to 39.3 (p < 0.001). Mean CESD score was reduced to 18.0 (p < 0.001), and the proportion of depressed patients fell from 79% to 54% (p = 0.003). Substance misuse was identified in 27 patients (32%). CONCLUSIONS: A primary care disease management program improved pain, depression, and disability scores over three months in a cohort of opioid-treated patients with chronic non-cancer pain. Substance misuse and depression were common, and many patients who had substance misuse identified left the program when they were no longer prescribed opioids. Effective care of patients with chronic pain should include rigorous assessment and treatment of these comorbid disorders and intensive efforts to insure follow up.

Adult↗

PubMed2005

Do physicians know when their diagnoses are correct? Implications for decision support and error reduction.

OBJECTIVE: This study explores the alignment between physicians' confidence in their diagnoses and the "correctness" of these diagnoses, as a function of clinical experience, and whether subjects were prone to over-or underconfidence. DESIGN: Prospective, counterbalanced experimental design. SETTING: Laboratory study conducted under controlled conditions at three academic medical centers. PARTICIPANTS: Seventy-two senior medical students, 72 senior medical residents, and 72 faculty internists. INTERVENTION: We created highly detailed, 2-to 4-page synopses of 36 diagnostically challenging medical cases, each with a definitive correct diagnosis. Subjects generated a differential diagnosis for each of 9 assigned cases, and indicated their level of confidence in each diagnosis. MEASUREMENTS AND MAIN RESULTS: A differential was considered "correct" if the clinically true diagnosis was listed in that subject's hypothesis list. To assess confidence, subjects rated the likelihood that they would, at the time they generated the differential, seek assistance in reaching a diagnosis. Subjects' confidence and correctness were "mildly" aligned (kappa=.314 for all subjects, .285 for faculty, .227 for residents, and .349 for students). Residents were overconfident in 41% of cases where their confidence and correctness were not aligned, whereas faculty were overconfident in 36% of such cases and students in 25%. CONCLUSIONS: Even experienced clinicians may be unaware of the correctness of their diagnoses at the time they make them. Medical decision support systems, and other interventions designed to reduce medical errors, cannot rely exclusively on clinicians' perceptions of their needs for such support.

Clinical Competence↗

PubMed2004

Electron attachment and detachment: electron affinities of isomers of trifluoromethylbenzonitrile.

Rate constants for electron attachment to the three isomers of trifluoromethylbenzonitrile [(CF(3))(CN)C(6)H(4), or TFMBN] were measured over the temperature range of 303-463 K in a 133-Pa He buffer gas, using a flowing-afterglow Langmuir-probe apparatus. At 303 K, the measured attachment rate constants are 9.0 x 10(-8) (o-TFMBN), 5.5 x 10(-8) (m-TFMBN), and 8.9 x 10(-8) cm(3) s(-1) (p-TFMBN), estimated accurate to +/-25%. The attachment process formed only the parent anion in all three cases. Thermal electron detachment was observed for all three anion isomers, and rate constants for this reverse process were also measured. From the attachment and detachment results, the electron affinities of the three isomers of TFMBN were determined to be 0.70(o-TFMBN), 0.67(m-TFMBN), and 0.83 eV (p-TFMBN), all +/-0.05 eV. G3(MP2) [Gaussian-3 calculations with reduced Møller-Plesset orders (MP2)] calculations were carried out for the neutrals and anions. Electron affinities derived from these calculations are in good agreement with the experimental values.

Journal Article↗

PubMed2004

Reactions of N+, N2+, and N3+ with NO from 300 to 1400 K.

Rate constants have been measured from 300 to 1400 K in a selected ion flow tube (SIFT) and a high temperature flowing afterglow for the reactions of N+, N2+ and N3+ with NO. In all of the systems, the rate constants are substantially less than the collision rate constant. Comparing the high temperature results to kinetics studies as a function of translational energy show that all types of energy (translational, rotational, and vibrational) affect the reactivity approximately equally for all three ions. Branching ratios have also been measured at 300 and 500 K in a SIFT for the N+ and N3+ reactions. An increase in the N2+ product at the expense of NO+ nondissociative charge transfer product occurs at 500 K with N+. The branching ratios for the reaction of N3+ with NO have also been measured in the SIFT, showing that only nondissociative charge transfer giving NO+ occurs up to 500 K. The current results are discussed in the context of the many previous studies of these ions in the literature.

Journal Article↗

PubMed2004

Electron attachment and detachment and the electron affinity of cyclo-C4F8.

New measurements have been made of rate constants for electron attachment to c-C(4)F(8) (octafluorocyclobutane) and thermal electron detachment from the parent anion, c-C(4)F(8) (-), over the temperature range 298-400 K in 133 Pa of He gas in a flowing-afterglow Langmuir-probe apparatus. From these data the electron affinity for c-C(4)F(8) was determined, EA(c-C(4)F(8))=0.63+/-0.05 eV. The motivation was to resolve a discrepancy between our earlier EA estimate and a higher value (EA=1.05+/-0.10 eV) reported from a recent experiment of Hiraoka et al. [J. Chem. Phys. 116, 7574 (2002)]. The electron attachment rate constant is 9.3+/-3.0x10(-9) cm(3) s(-1) at 298 K. The electron detachment rate constant is negligible at room temperature but climbs to 1945+/-680 s(-1) at 400 K. G3(MP2) calculations were carried out for the neutral (D(2d), (1)A(1)) and anion (D(4h), (2)A(2u)) and yielded EA(c-C(4)F(8) (-))=0.595 eV. Bond energies were also calculated for loss of F from c-C(4)F(8) and loss of F or F(-) from c-C(4)F(8) (-). From these, dissociative electron attachment is found to be endothermic by at least 1.55 eV.

Journal Article↗

PubMed2004

Electron attachment to PSCl3.

Electron attachment to PSCl3 was studied in 133-Pa pressure of helium gas at temperatures from 298-550 K. Measurements of rate constants and branching fractions were made in a flowing-afterglow Langmuir-probe (FALP) apparatus. These experiments yielded an electron attachment rate constant of 5.1 x 10(-8) cm3 s(-1) that was found not to change significantly in the 298-550 K temperature range. This rate constant represents an attachment efficiency of about 14%. Attachment in 133 Pa of He gas yielded only the dissociative ion products PSCl2- and Cl-. The FALP data suggest that there is an activation energy of about 17 meV for production of PSCl2-. Attachment to PSCl3 was also studied at high pressure (9-93 kPa) of N2 in an ion mobility mass spectrometer, at 298 K. In contrast to the low-pressure data, the parent anion product channel (PSCl3-) was observed (along with the dissociative channels), and increased in importance with N2 pressure. Gaussian-3 (G3) calculations were carried out for PSCl3 and PSCl2 neutrals and anions to aid in interpretation of the experimental results. The calculations indicate that the electron affinity EA(PSCl2) is slightly smaller than EA(Cl), which may account for the observed branching fractions for PSCl2- and Cl- in the low-pressure experiments. A natural population analysis was performed to obtain the charges associated with each atom in the molecules in order to estimate how the attached electron is distributed. Comparison is made between the present study of electron attachment to PSCl3 and our earlier work on attachment to POCl3, and G3 calculations are reported here for neutral and anionic POCl2 and POCl3. In contrast to PSCl2, the calculations imply that EA(POCl2) is slightly greater than EA(Cl). For both PSCl3 and POCl3, the calculations show that the dissociative electron attachment process is close to thermoneutral.

Journal Article↗

PubMed2003

Direct measurement of the thermal rate coefficient for electron attachment to ozone in the gas phase, 300-550 K: implications for the ionosphere.

Attachment of thermal electrons to O3 was studied in 133 Pa He between 300-550 K; the process is extremely inefficient. The rate coefficient increases sharply with temperature from 0.9 to 5 x 10(-11) cm(3) s(-1) (+/-30%) and comparison to kinetic energy measurements suggests internal energy can drive the reaction. These determinations account for competing processes of diffusion, recombination, and electron detachment reactions, and imply that no significant zero-energy resonance cross section exists, contradicting recent electron-beam results that call for substantial revision of ionospheric models.

Journal Article↗

PubMed2002

Exploring the boundaries of plausibility: empirical study of a key problem in the design of computer-based clinical simulations.

All clinical simulation designers face the problem of identifying the plausible diagnostic and management options to include in their simulation models. This study explores the number of plausible diagnoses that exist for a given case, and how many subjects must work up a case before all plausible diagnoses are identified. Data derive from 144 residents and faculty physicians from 3 medical centers, each of whom worked 9 diagnostically challenging cases selected from a set of 36. Each subject generated up to 6 diagnostic hypotheses for each case, and each hypothesis was rated for plausibility by a clinician panel. Of the 2091 diagnoses generated, 399 (19.1%), an average of 11 per case, were considered plausible by study criteria. The distribution of plausibility ratings was found to be statistically case dependent. Averaged across cases, the final plausible diagnosis was generated by the 28th clinician (sd = 8) who worked the case. The results illustrate the richness and diversity of human cognition and the challenges these pose for creation of realistic simulations in biomedical domains.

Computer Simulation↗

PubMedDate not supplied

Data collection in a multisite project: Teleform.

Data collection, entry, validation, and management are salient time- and resource-consuming dimensions of all research projects. This is especially true for multisite studies, which pose unique, additional challenges because of their research design requirements. To save time and reduce the number of manual data entry errors, automated processing systems are becoming more widely used. Our research team chose Teleform for data entry and collection for the Smoking Cessation or Reduction in Pregnancy Trial study. This article presents our experience with this new technology.

Alabama↗