Substitution of a hydroxamic acid anchor into the MK-2 dye for enhanced photovoltaic performance and water stability in a DSSC.

An efficient synthetic protocol to functionalize the cyanoacrylic acid anchoring group of commercially available MK-2 dye with a highly water-stable hydroxamate anchoring group is described. Extensive characterization of this hydroxamate-modified dye (MK-2HA) reveals that the modification does not affect its favorable optoelectronic properties. Dye-sensitized solar cells (DSSCs) prepared with the MK-2HA dye attain improved efficiency (6.9%), relative to analogously prepared devices with commercial MK-2 and N719 dyes. The hydroxamate anchoring group also contributes to significantly increased water stability, with a decrease in the rate constant for dye desorption of MK-2HA relative to MK-2 in the presence of water by as much as 37.5%. In addition, the hydroxamate-anchored dye undergoes essentially no loss in DSSC efficiency and the external quantum efficiency improves when up to 20% water is purposefully added to the electrolyte. In contrast, devices prepared with the commercial dye suffer a 50% decline in efficiency under identical conditions, with a concomitant decrease in external quantum efficiency. Collectively, our results indicate that covalent functionalization of organic dyes with hydroxamate anchoring groups is a simple and efficient approach to improving the water stability of the dye-semiconductor interface and overall device durability.

Computed ligand electronic parameters from quantum chemistry and their relation to Tolman parameters, Lever parameters, and Hammett constants.

The calculated (DFT, B3PW91) A(1) nu(CO) frequency in LNi(CO)(3) defines an electronic parameter that reliably predicts the relative donor powers of a wide variety of cationic, neutral, and negatively charged ligands. These calculated parameters correlate very well with the available Tolman and Lever parameters, and also with Hammett's sigma(m), where available. The method avoids any experimental limitations and, in particular, can be used for proposed ligands not yet experimentally available.

Characterization of the O(2)-evolving reaction catalyzed by [(terpy)(H2O)Mn(III)(O)2Mn(IV)(OH2)(terpy)](NO3)3 (terpy = 2,2':6,2"-terpyridine).

The complex [(terpy)(H(2)O)Mn(III)(O)(2)Mn(IV)(OH(2))(terpy)](NO(3))(3) (terpy = 2,2':6,2' '-terpyridine) (1)catalyzes O(2) evolution from either KHSO(5) (potassium oxone) or NaOCl. The reactions follow Michaelis-Menten kinetics where V(max) = 2420 +/- 490 mol O(2) (mol 1)(-1) hr(-1) and K(M) = 53 +/- 5 mM for oxone ([1] = 7.5 microM), and V(max) = 6.5 +/- 0.3 mol O(2) (mol 1)(-1) hr(-1) and K(M) = 39 +/- 4 mM for hypochlorite ([1] = 70 microM), with first-order kinetics observed in 1 for both oxidants. A mechanism is proposed having a preequilibrium between 1 and HSO(5-) or OCl(-), supported by the isolation and structural characterization of [(terpy)(SO(4))Mn(IV)(O)(2)Mn(IV)(O(4)S)(terpy)] (2). Isotope-labeling studies using H(2)(18)O and KHS(16)O(5) show that O(2) evolution proceeds via an intermediate that can exchange with water, where Raman spectroscopy has been used to confirm that the active oxygen of HSO(5-) is nonexchanging (t(1/2) >> 1 h). The amount of label incorporated into O(2) is dependent on the relative concentrations of oxone and 1. (32)O(2):(34)O(2):(36)O(2) is 91.9 +/- 0.3:7.6 +/- 0.3:0.51 +/- 0.48, when [HSO(5-)] = 50 mM (0.5 mM 1), and 49 +/- 21:39 +/- 15:12 +/- 6 when [HSO(5-)] = 15 mM (0.75 mM 1). The rate-limiting step of O(2) evolution is proposed to be formation of a formally Mn(V)=O moiety which could then competitively react with either oxone or water/hydroxide to produce O(2). These results show that 1 serves as a functional model for photosynthetic water oxidation.

The relative impact of generic head-related transfer functions on auditory speech thresholds: implications for the design of three-dimensional audio displays.

BACKGROUND: Auditory speech thresholds were measured in this study. METHODS: Subjects were required to discriminate a female voice recording of three-digit numbers in the presence of diotic speech babble. The voice stimulus was spatialized at 11 static azimuth positions on the horizontal plane using three different head-related transfer functions (HRTFs) measured on individuals who did not participate in this study. The diotic presentation of the voice stimulus served as the control condition. RESULTS: The results showed that two of the HRTFS performed similarly and had significantly lower auditory speech thresholds than the third HRTF. All three HRTFs yielded significantly lower auditory speech thresholds compared with the diotic presentation of the voice stimulus, with the largest difference at 60 degrees azimuth. CONCLUSION: The practical implications of these results suggest that lower headphone levels of the communication system in military aircraft can be achieved without sacrificing intelligibility, thereby lessening the risk of hearing loss.

The evolutionary enigma of bonefishes (Albula spp.): cryptic species and ancient separations in a globally distributed shorefish.

Many examples of cryptic marine species have been demonstrated with biochemical and molecular studies. In most cases, a broadly distributed taxon is actually a group of sibling species that can be distinguished (upon closer examination) by ecological or morphological characters. Fishes of the family Albulidae constitute a notable exception. Bonefish (Albula spp.) morphology and ecology are highly conserved around the globe, and their extended pelagic larval stage could allow population connections on a vast geographic scale. Based on this perceived homogeneity, bonefishes were classified as a single pantropical species, A. vulpes. However, allozyme studies of Hawaiian populations indicated that two sympatric species (A. glossodonta and A. neoguinaica) are included in the synonymy of A. vulpes. To ascertain the number and distribution of evolutionary partitions in Albula, we surveyed 564 bp of mitochondrial DNA (mtDNA) cytochrome b from 174 individuals collected at 26 locations. Sequence comparisons reveal eight deep lineages (d = 5.56-30.6%) and significant population structure within three of the four lineages that could be tested (phiST = 0.047-0.678). These findings confirm the genetic distinctiveness of the three species noted above and invoke the possibility of five additional species. Clock estimates for mtDNA indicate that these putative species arose 4-20 million years ago. Distinct evolutionary lineages coexist in several sample locations, yet show little morphological or ecological differentiation in sympatry. Thus, bonefish species seem to defy the evolutionary conventions of morphological differentiation over time and ecological displacement in sympatry. Despite multiple cases of sympatry, sister-taxa relationships inferred from mtDNA indicate that divergence in allopatry has been the predominant speciation mechanism in Albula. Stabilizing selection in the homogeneous habitat occupied by bonefishes (tropical sand flats) could promote the retention of highly conserved morphology and ecology.

The mechanism of the Ni-Fe hydrogenases: a quantum chemical perspective.

The catalytic cycle for the heterolytic splitting of H2 by Ni-Fe hydrogenase has been investigated in four recent quantum chemical studies. The mechanisms proposed are described and compared. Although there are clear differences in these mechanisms and in the assignments of the different states observed experimentally, there are also important points of concensus.

High-frequency EPR study of a new mononuclear manganese(III) complex:. [(terpy)Mn(N3)3] (terpy = 2,2':6',2''-terpyridine).

The isolation and structural characterization of [(terpy)Mn(III)(N3)3], complex 1, is reported (terpy = 2,2':6',2' '-terpyridine). Complex 1, a product of the reaction between the mixed-valence dimer [(terpy)(H2O)Mn(III)(O)2Mn(IV)(OH2)(terpy)](NO3)3 and NaN3, crystallizes in a triclinic system, space group P1, a = 8.480(1) A, b = 8.9007(2) A, c = 12.109(2) A, alpha = 93.79(1) degrees, beta = 103.17(1) degrees, gamma = 103.11(1) degrees, and Z = 2. Complex 1 exhibits a Jahn-Teller distortion of the octahedron characteristic of a six-coordinated high-spin Mn(III). A vibrational spectroscopic study was performed. The nu(asym)(N3) mode of complex 1 appears in the IR as a strong band at 2035 cm(-1) with a less intense feature at 2072 cm(-1), and in the FT-Raman as a strong band at 2071 cm(-1) with a weaker broad band at 2046 cm(-1). The electronic properties of complex 1 were investigated using a high-field and high-frequency EPR study (190-475 GHz). The different spin Hamiltonian parameters have been determined (D = -3.29 (+/-0.01) cm(-1), E = 0.48 (+/-0.01) cm(-1), E '= 0.53 (+/-0.01) cm(-1), g(x) = 2.00 (+/-0.005), g(y) = 1.98 (+/-0.005), g(z) = 2.01 (+/-0.005)). These parameters are in agreement with the geometry of complex 1 observed in the crystal structure, a D < 0 related to the elongated distortion, and a value of E/D close to 0.2 as expected from the highly distorted octahedron. The two values of the E-parameter are explained by the presence of two slightly different structural forms of complex 1 in the crystal lattice. A second hypothesis was explored to explain the experimental data. The calculation for the simulation was done taking into account that the g and D tensors are not collinear due to the low symmetry of complex 1. In that case, the spin Hamiltonian parameters found are D = -3.29 (+/-0.01) cm(-1), E = 0.51 (+/-0.01) cm(-1), g(x) = 2.00 (+/-0.005), g(y) = 1.98 (+/-0.005), and g(z) = 2.01 (+/-0.005).

Abnormal binding in a carbene complex formed from an imidazolium salt and a metal hydride complex.

2-Pyridylmethylimidazolium salts and IrH5(PPh3)2 give an [(N-C)IrH2(PPh3)2]+ species with the imidazole ring bound in the 'wrong way': at C-5, not at the expected C-2.

Higher professional education for general practitioners: postal questionnaire survey.

BACKGROUND: There is no consensus about whether higher professional education (HPE) is necessary for general practitioners (GPs) to complete their vocational training. AIM: To investigate beliefs about the need for HPE, its funding, duration, curriculum, and whether new principals (NPs) are eligible to undertake it. METHOD: A confidential postal questionnaire was sent to senior partners, GP registrars, NPs, GP trainers, and GP tutors, principally in the old South West region of England, and nationally to other 'academic' GPs. RESULTS: Of 1199 GPs, 750 (62.6%) replied; 561 (79.2%) responders agreed with the principle of HPE for NPs, especially members of the Royal College of General Practitioners and academic GPs; senior partners (SPs) were less likely to agree (all P < 0.001). Of 700 GPs, 331 (50.3%) believed that HPE should last one or two years, 66.4% agreed that NPs should have a major input into the HPE curriculum, and 54.6% agreed that health authorities should be major sources of funding, together with the postgraduate deans (29.9%). GP tutors and trainers should have the main responsibility for teaching HPE. The principal barriers to setting up a HPE course are the financial cost, the time cost, difficulty in changing the status quo, and various practical problems. The facilitatory influences are: the enthusiasm of the NPs and of their clinical colleagues, an appropriate educational environment, a high quality clinical base, and recognition that NPs have specific needs. Of 668 GPs, 89.7% would release NPs if an HPE course were free and locums were paid, although SPs were less likely to agree (P < 0.001); if the HPE course cost the practice money, then only 30.6% would release NPs. CONCLUSION: If adequately externally funded, then there is widespread support for HPE with most GPs willing to release NPs. NPs and existing GP teachers should decide the curriculum. Its aim should be to provide educational support for NPs during the transition from GP registrar to fully-trained GP principal.

Higher professional education for general medical practitioners: key informant interviews and focus group findings.

BACKGROUND: If higher professional education (HPE) for general practitioners (GPs) is to be implemented, then key stakeholders will need to be supportive. AIM: To investigate stakeholders' beliefs about the concept of HPE, its funding, and relationships to education and care. METHOD: Interviews were conducted using a topic guide with a health authority (HA) representative, the Local Medical Committee Chair, the Medical Audit Advisory Group Chair, a GP tutor from each of the six health authorities in the old South West region, and a senior member of the three academic GP departments and the two Royal College of General Practitioners faculties in the region. Focus groups were held with GP registrars on both vocational training schemes (VTSs) and on the one HPE course in the region. These were recorded, transcribed verbatim, and analysed for emergent themes that were triangulated with the ideas expressed in the focus groups; the same topic guide was used for both. RESULTS: Of 29 key informants, 24 were interviewed. Six focus groups were held (the one HPE group and five out of the nine VTSs), after which no new ideas emerged. There is a transition period, after becoming a new principal (NP) and before becoming a fully competent independent GP, during which NPs need support. Benefits would include receiving peer support to reduce stress during the transition, enhanced non-clinical competencies, becoming a better skilled GP, avoiding the negative personal impact of a career as a GP, and helping recruitment. To improve patient care there must be a link between education and service provision. Funding is the major consideration in setting HPE; mixed funding is best coming from top-sliced General Medical Services (GMS), the HA, and regional educational funds. Barriers might include NPs' practice workload, their enthusiasm, and their partners' attitudes. The other key is a local enthusiast to initiate a course and coordinate the 'players'. The curriculum would be principally non-clinical and should be agreed by learners and the course tutor together, taking advice from various interested parties. CONCLUSION: There is a need for HPE for new NPs. It will require funding external to individual practices or NPs and a local enthusiast. Top-slicing of GMS funds is one source of funding, with additional funds from regional education and HAs. HPE must be related to service provision, to NP needs, and to vocational training.

Release from masking in virtual auditory space during sustained positive acceleration.

BACKGROUND: The use of a three-dimensional (3-D) auditory display to significantly lower subject detection level while maintaining comprehension under sustained positive G-stress was explored in this study. METHODS: Auditory threshold levels were measured for detecting a band limited pulsed signal in the presence of a broadband diotic masker at both + 1 Gz (rest position) and under sustained +3 Gz. The pulsed signal was presented diotically and was spatialized at one of four static azimuth positions on the horizontal plane. RESULTS: Results showed that auditory thresholds were not significantly affected by sustained +3 Gz stress. Compared with a diotic presentation, subjects reached an average of 6.8 dB lower auditory threshold at +1 Gz and under sustained +3 Gz when the pulsed signal was spatialized at a static position of 90 degrees azimuth on the horizontal plane. CONCLUSION: The implication of these results and suggestions for further research are discussed.

A functional model for O-O bond formation by the O2-evolving complex in photosystem II.

The formation of molecular oxygen from water in photosynthesis is catalyzed by photosystem II at an active site containing four manganese ions that are arranged in di-mu-oxo dimanganese units (where mu is a bridging mode). The complex [H2O(terpy)Mn(O)2Mn(terpy)OH2](NO3)3 (terpy is 2,2':6', 2"-terpyridine), which was synthesized and structurally characterized, contains a di-mu-oxo manganese dimer and catalyzes the conversion of sodium hypochlorite to molecular oxygen. Oxygen-18 isotope labeling showed that water is the source of the oxygen atoms in the molecular oxygen evolved, and so this system is a functional model for photosynthetic water oxidation.

Serological survey for diseases in free-ranging coyotes (Canis latrans) in Yellowstone National Park, Wyoming.

From October 1989 to June 1993, we captured and sampled 110 coyotes (Canis latrans) for various diseases in Yellowstone National Park, Wyoming (USA). Prevalence of antibodies against canine parvovirus (CPV) was 100% for adults (> 24 months old), 100% for yearlings (12 to 24 months old), and 100% for old pups (4 to 12 months old); 0% of the young pups (< 3 months old) had antibodies against CPV. Presence of antibodies against canine distemper virus (CDV) was associated with the age of the coyote, with 88%, 54%, 23%, and 0% prevalence among adults, yearlings, old pups, and young pups, respectively. Prevalence of CDV antibodies declined over time from 100% in 1989 to 33% in 1992. The prevalence of canine infectious hepatitis (ICH) virus antibodies was 97%, 82%, 54%, and 33%, for adults, yearlings, old pups, and young pups, respectively. The percentage of coyotes with ICH virus antibodies also declined over time from a high of 100% in 1989 to 31% in 1992, and 42% in 1993. Prevalence of antibodies against Yersinia pestis was 86%, 33%, 80%, and 7%, for adults, yearlings, old pups, and young pups, respectively, and changed over time from 57% in 1991 to 0% in 1993. The prevalence of antibodies against Francisella tularensis was 21%, 17%, 10%, and 20%, for adults, yearlings, old pups, and young pups, respectively. No coyotes had serologic evidence of exposure to brucellosis, either Brucella abortus or Brucella canis. No coyotes were seropositive to Leptospira interrogans (serovars canicola, hardjo, and icterohemorrhagiae). Prevalence of antibodies against L. interrogans serovar pomona was 7%, 0%, 0%, and 9%, for adults, yearlings, old pups, and young pups, respectively. Antibodies against L. interrogans serovar grippotyphosa were present in 17% of adults and 0% of yearlings, old pups, and young pups. Many infectious canine pathogens (CPV, CDV, ICH virus) are prevalent in coyotes in Yellowstone National Park, with CPV influencing coyote pup survival during the first 3 months of life; eight of 21 transmitted pups died of CPV infection in 1992. The potential impact of these canine pathogens on wolves (C. lupus) reintroduced to Yellowstone National Park remains to be documented.

Enhanced radiation-induced cell killing by carboplatin in cells of repair-proficient and repair-deficient cell lines.

The objective of this study was to determine whether a deficiency for either one of two repair processes influences the phenomenon of enhancement of radiation-induced cell killing by carboplatin which has been reported previously in one cell line (V79) and which is presumably a result of an interaction between these two therapeutic modalities. Cell killing was enhanced in cells of four cell lines when the cells were exposed to carboplatin before and during irradiation in either air or hypoxia. In cell lines proficient in both excision repair and DNA double-strand break repair (K1 and AA8), and in a cell line deficient in nucleotide excision repair (UV41), the enhancement was characterized as both a reduction in the shoulder region of the survival curves indicated by a reduced Dq and a reduction in D0 in the terminal region of the survival curves determined for cells exposed in air and under hypoxic conditions. Only the latter effect was observed in a cell line deficient in DNA double-strand break repair (xrs-5). The survival curves were fitted to the data using the repair saturation model and a computer program developed by N. Albright (Radiat. Res. 118, 112-130, 1989). In hypoxia, the reductions in Dq were as great as from 7.0 Gy to 2.1 Gy, 3.3 Gy to 0 Gy and 1.7 Gy to 0 Gy for K1, AA8 and UV41 cells, respectively. Sensitizer enhancement ratios ranged from 1.3 to 1.7 and were similar for irradiation in air and under hypoxic conditions. This enhanced cell killing by carboplatin combined with radiation required levels of the drug sufficient to produce cytotoxicity by the drug alone as exemplified by the UV41 cell line, which is intrinsically sensitive to carboplatin and in which 1/30 of the drug concentration required for the other cell lines produced an enhanced cell killing at an equitoxic dose of only 5 microM.

Nurses in ambulatory care: multiple roles and opportunities. Interview by Susan Cummings.

This article presents an interview with a dynamic health care professional who has extensive experience in providing nursing care in ambulatory care settings. Crabtree's candid and timely responses add to the pursuit of the answers to the question that is the title of this issue: "Managing Care: Who's Accountable?"