bluuebunny/crossref_metadata_2025 huggingface dataset:
Microbial toxicity assays used for water quality evaluation in South Africa
Authors: Slabbert J. L.
Published: October 2006

A number of microbial assays have been developed for the detection of toxic chemicals in water. These include bacterial and protozoan oxygen uptake assays, a bacterial growth test, a colony formation test, and a microassay. The bioassays are rapid and relatively simple, cost effective and sensitive, and have been applied to the toxicity evaluation of drinking water and wastewaters. These tests have been used as a valuable part of a battery of bioassays that also include other, more time‐consuming biological tests.
Battery of screening tests approach applied to sediment extracts
Authors: Dutka B. J. , Kwan K. K.
Published: October 2006

This paper reports the application of a battery of microbiological and toxicant screening tests to sediments collected from the Port Hope area. The sediments were extracted using Milli‐Q water and solvents. The solvent extracts indicated that the whole sampling area has been impacted by toxic chemicals. The Daphnia magna test was the most sensitive screening test in Milli‐Q water extracts. Microbiological studies indicated that the sampling area was, and is continuing to be, impacted by fecal pollution.
Development of a field test kit for coliphage detection in natural waters
Authors: Loh C. L. , Jangi M. S. , Ho Y. C. , Ngeow Y. F. , Wang C. W.
Published: October 2006

Coliphages may be suitable alternative indicators of fecal pollution in natural waters. The relationship between coliphage and fecal coliform numbers may be expressed by log10 transformed linear regression equations in surface waters (correlation coefficient, r2 = 0.5872; p < 0.001) and in well waters (r2 = 0.4767; p < 0.001). Using the American Public Health Association 919C single agar layer method, coliphages can be enumerated easily and at less cost and more rapidly than coliform enumeration methods. In adapting this test for use in a field test kit, however, further modifications and simplifications are required.

The use of 2,3,5‐triphenyl tetrazolium chloride (TPTZ) to enhance plaque visibility while helpful, was not essential. Matched‐pair t‐test analysis showed no significant difference between the plaque numbers enumerated with or without TPTZ to help plaque visibility.

The Escherichia coli C host bacteria can be maintained either as a frozen preparation or dried on to paper disks with protective milk colloids. In the latter procedure, a resuscitation period of 18–24 h in broth at 30°C was found to be satisfactory in giving plaque numbers in the test that were not significantly different than when frozen host was used.

A portable field kit has been designed to carry out a total of eight tests. The kit includes the media, the bacterial host, petri dishes, syringes, receptacles, and a camping gas cylinder. It measures 38 cm by 25.5 cm by 33.5 cm and weighs about 6.4 kg. Using the kit, the test procedure for a water sample can be carried out in under 15 min.
Is the Lichtenstein Operation of Strangulated Groin Hernia a Safe Procedure?
Authors: Wysocki Andrzej , Kulawik Jan , Poźniczek Marek , Strzałka Marcin
Published: October 2006

Background

In spite of many published articles describing the hernia repairs, there are only a few original reports concerning the polymer mesh application during emergency procedures for strangulated inguinal hernias. The aim of our study was to evaluate the results of the Lichtenstein and Bassini operations for strangulated groin hernias and to show the changing number of the tension‐free repairs.

Methods

From 1997 to 2004, the Bassini procedure was performed in 21 patients, 6 of whom underwent small intestine resection and 2 others required resection of the necrotic omentum. The strangulated intestinal loop or omentum were released in 13 cases. After the repair 1 patient died of shock caused by intestinal necrosis. Of 56 patients who underwent an emergency Lichtenstein procedure, 55 were followed‐up. A small intestine resection was performed in 2 cases to correct segmental necrosis. The gangrenous omental appendix of the sigmoid colon was excised in 1 patient, and necrotic omental fragments were resected in 2 cases. The strangulated intestinal loop or omentum was released in 51 patients. All patients were given wide‐spectrum antibiotics intravenously.

Results

Between 1997 and 2000 tension‐free procedures were performed in half of the patients undergoing emergency operation for strangulated hernia; between 2001 and 2004 such procedures were employed in more than 90% of the cases. In 2 patients we observed a small inflammatory infiltration of the wound that resolved within several days after Lichtenstein repair. A serous fluid collection was present in 2 cases. The treatment consisted of puncture and was successful in both cases.

Conclusions

The use of monofilament polypropylene mesh for strangulated inguinal hernia repair is safe, and the risk of the local infectious complications is low.
Combined Low Pressure Pneumoperitoneum and Intraperitoneal Infusion of Normal Saline for Reducing Shoulder Tip Pain Following Laparoscopic Cholecystectomy
Authors: Esmat M. Emad , Elsebae Magdy M.A. , Nasr Magid M.A. , Elsebaie Sameh B.
Published: October 2006

Introduction

Intraabdominal CO2 gas after laparoscopic cholecystectomy causes postoperative shoulder‐tip pain. Many methods of analgesia have been used to reduce this pain, including analgesic drugs, intraperitoneal local anesthetic, intraperitoneal saline, a gas drain, heated gas, low‐pressure gas, and nitrous oxide pneumoperitoneum. The aim of this study was to evaluate the efficacy of combined low‐pressure CO2 pneumoperitoneum and intraperitoneal infusion of normal saline in reducing the incidence of postoperative shoulder‐tip pain.

Methods

Altogether, 109 patients undergoing elective laparoscopic cholecystectomy were randomized prospectively into three groups. Patients in group A (n = 34) underwent laparoscopic cholecystectomy with 14 mmHg CO2 pneumoperitoneum; patients in group B (n = 37) underwent laparoscopic cholecystectomy with 10 mmHg CO2 pneumoperitoneum; and those in group C (n = 38) underwent laparoscopic cholecystectomy with 10 mmHg CO2 pneumoperitoneum in addition to intraperitoneal normal saline infusion in the right hemidiaphragmatic area. Shoulder‐tip pain was recorded on a verbal rating scale 2, 6, 12, 24, and 48 hours after operation.

Results

Twelve patients in group A (35.2 percent), six in group B (16.2 percent), and seven in group C (18.4 percent) complained of shoulder‐tip pain. Hence, there was a significant decrease in the frequency of shoulder‐tip pain in groups B and C in relation to group A, but there was no significant difference between groups B and C. The postoperative shoulder‐tip pain scores were significantly reduced in group C at 6, 12, and 24 hours. The number of patients who required additional analgesics was also reduced in group C.

Conclusions

Low‐pressure CO2 pneumoperitoneum reduces the number of patients complaining of shoulder‐tip pain and the intensity of the pain after laparoscopic cholecystectomy. The addition of intraperitoneal normal saline infusion to low‐pressure CO2 pneumoperitoneum seems to reduce the intensity but not the frequency of shoulder‐tip pain after laparoscopic cholecystectomy.
Interim Results of Sentinel Node Biopsy during Laparoscopic Gastrectomy: Possible Role in Function‐Preserving Surgery for Early Cancer
Authors: Saikawa Yoshiro , Otani Yoshihide , Kitagawa Yuko , Yoshida Masashi , Wada Norihito , Kubota Tetsuro , Kumai Koichiro , Sugino Yoshinori , Mukai Makio , Kameyama Kaori , Kubo Atsushi , Kitajima Masaki
Published: October 2006

Introduction

Intraoperative detection of sentinel nodes (SNs) has been used clinically to predict regional lymph node (LN) metastasis in patients with breast cancer and malignant melanoma. Intraoperative lymphatic mapping and SN biopsy can potentially be combined with minimally invasive surgery. However, few reports have demonstrated the validity of SN biopsy during laparoscopic gastrectomy. The aim of this study was to investigate the feasibility and accuracy of laparoscopic lymphatic mapping in predicting LN status in patients with gastric cancer.

Methods

A total of 35 patients with gastric cancer diagnosed preoperatively as T1, N0 were enrolled. Endoscopic injection of technetium‐99m‐radiolabeled tin colloid was completed 16 hours before surgery, and radioactive SNs were identified with a gamma probe intraoperatively. Isosulfan blue dye was injected endoscopically during the operation. Laparoscopy‐assisted gastrectomy with LN dissection was performed. All resected LNs were evaluated by routine pathology examination.

Results

SNs were detected in 33 (94.3%) of 35 patients. The mean number of SNs was 3.9, and the diagnostic accuracy according to SN status was 97.0% (32/33), as one patient with a false‐negative result was observed. The patient with the false‐negative specimen was finally diagnosed as having advanced gastric cancer with invasion into the proper muscular layer and severe lymphatic vessel invasion, causing destruction of normal lymphatic flow by the tumor.

Conclusions

Radio‐guided SN mapping during laparoscopic gastrectomy is an accurate diagnostic tool for detecting lymph node metastasis in patients with early‐stage gastric cancer. Validation of this method requires further studies on technical issues, including indications, tracers, methods of lymph node retrieval, and diagnostic modalities of metastasis.
Toward a risk assessment of central Aegean volcanoes
Authors: Hübscher Christian , Hensch Martin , Dahm Torsten , Dehghani Ali , Dimitriadis Iordanis , Hort Matthias , Taymaz Tuncay
Published: October 2006

Active tectonic processes along the African‐Eurasian collision zone are associated with catastrophic events including earthquakes, major volcanic eruptions, and tsunamis. Understanding how these processes can affect the eastern Mediterranean is of increasing scientific and public interest. The region includes a frequently crossed international sea traffic corridor and dense population centers. Furthermore, most of the small volcanic islands in the Aegean are major tourist attractions that contribute significantly to the wealth of this region.
Antarctic Shallow Drilling Project provides key core samples
Authors: Anderson John B. , Smith Wellner Julia , Bohaty Steve , Manley Patricia L. , Wise Sherwood W.
Published: October 2006

The understanding of Antarctica's climate, cryosphere, and biosphere evolution is limited, which is due in part to the paucity of outcrops and cores that record changes during the Tertiary. This problem has been partially rectified using conventional drill ships, such as the JOIDES Resolution, but access to key areas of the continental margin has been restricted because of the inability of these ships to operate in ice‐covered waters. While researchers are restricted in their ability to acquire long cores in ice‐prone areas, nature has provided an alternative method.

During past glacial maxima, ice sheets advanced onto the continental shelf, eroding deeply into the stratigraphic section. Several areas of the shelf are characterized by seaward dipping strata a few meters beneath the seafloor. However, these older strata are overlaid by glacial sediments that have proven to be impenetrable by standard piston coring. The Shallow Drilling Project (SHALDRIL) began with the idea of using an icebreaking vessel as the drill platform so that drilling could be conducted in areas that are inaccessible by standard drill ships.Though, even icebreaking vessels with a drill stem hanging beneath them are vulnerable to ever‐present changes in sea state, winds, and ice conditions. Thus, the approach, by necessity, needs to be one of ‘drill and run.’ Two cruises, in the austral falls of 2005 and 2006, have shown the efficacy of this approach.
A turning point in auroral physics
Authors: Bryant Duncan A.
Published: October 2006

Auroral studies have reached a turning point. It now seems clear that the ‘standard’ theory which claims that the electrons responsible for bright, curtain‐like auroral arcs gain their energy from static electric fields, is indefensible, while a theory which attributes the acceleration to plasma waves is poised as a possible successor.

It was approximately 100 years ago that the Norwegian mathematician and physicist Kristian Birkeland inferred that the aurora was a scintillation of the atmosphere caused by an influx of charged particles. Just over half a century later, McIlwain [1960] discovered, from pioneering rocket flights made from near the town of Churchill in Manitoba, Canada, that Birkeland was right, and that the particles were primarily electrons. Moreover, Mcllwain was able to deduce that the electrons producing a curtain‐like auroral arc exhibited a local maximum, or peak, in their energy spectrum. This conclusion was confirmed with progressively increasing resolution and sensitivity by Albert [1967] and others in the 1960s.
Barriers and bias hold back women in academic science
Authors: Zielinski Sarah
Published: October 2006

Underlying biases and discrimination result in barriers that prevent women in science and engineering from advancing in academic positions, according to an 18 September report from the U.S. National Academies.

‘What this report demonstrates is that despite years of talking about the problem, it still remains a huge problem,’ said Mary Lou Zoback, a retired U.S. Geological Survey seismologist and a member of the committee that commissioned the report, entitled ‘Beyond Bias and Barriers: Fulfilling the Potential of Women in Academic Science and Engineering.’
“Walking on water” and the geoscientists' fear of social controversy
Authors: Nof Doron
Published: October 2006

Communications with editors of 13 specialized scientific journals concerning the possible publication of a seemingly controversial manuscript, which was recently published, are analyzed. On the basis of this analysis, many geoscience editors (as well as many geoscientists) may b e reluctant to publish articles with social controversies extending beyond the natural sciences, particularly when these issues involve religion. This hinders the progress of the geosciences rather than advances it, as it creates a detrimental and artificial separation between the geosciences and society at large.

McKeague, Paldor, and I addressed the question of whether there is a natural explanation for ‘walking on water’ in the Sea of Galilee in an article published in the April issue of the Journal of Paleolimnology (JOPL), a journal that focuses on the reconstruction of lakes history (and hence is an ideal medium for this particular paper). We suggested in the paper (JOPL, 35, 417–439,2006) that the legend of Jesus walking on water might be rooted in unusual freezing events that took place over relatively small parts of the Sea of Galilee. Such events probably happened during several cold episodes (lasting hundreds of years) that occurred during the past 2500 years. Because of salty and warm springs that emptied into the lake, a localized ‘convection free’ freeze just above the plume created by the springs (covering an area of about 1000 square meters) probably occurred as a result of short cold spells lasting two to three days. These brief cold spells were superimposed on the much longer cold episodes that occur every 500–1000 years.
Investigation of EPA library closures requested
Authors: Zielinski Sarah
Published: October 2006

Three Democratic ranking members of the U.S. House of Representatives Science Committee have asked the U.S. Government Accountability Office to investigate the Bush Administration's plan to cut funding for the U.S. Environmental Protection Agency's (EPA) system of libraries by more than 30% in Fiscal Year 2007. The EPA already has closed one regional library and identified two others that will be closed on 1 October. The agency has said that the plan will save money without reducing access to environmental information. The congressmen expressed concern that the closures could harm EPA's ability to enforce environmental laws and could deprive the public of access to environmental information.
Characterization of the snake venom ligand [125I]‐DNP binding to natriuretic peptide receptor‐A in human artery and potent DNP mediated vasodilatation
Authors: Singh G , Maguire J J , Kuc R E , Skepper J N , Fidock M , Davenport A P
Published: October 2006

Background and purpose:

The natriuretic peptides, ANP and BNP, modulate vascular smooth muscle tone in human conduit arteries. Surprisingly, the natriuretic peptide receptor‐A (NPR‐A) has not been visualized using radioligand binding in these vessels. A new member of this peptide family, Dendroaspis natriuretic peptide (DNP) identified from snake venom, has been proposed to be present in human plasma and endothelial cells. Also, recently a novel radioligand, [125I]‐DNP, has been characterized as selective for NPR‐A in human heart.

Experimental approach:

Our aims were to investigate expression and function of NPR‐A receptors in human mammary artery using [125I]‐DNP to quantify receptor density, immunocytochemistry to delineate the cellular distribution of the receptor and in vitro pharmacology to compare DNP induced vasodilatation to that of ANP.

Key results:

Saturable, sub‐nanomolar affinity [125I]‐DNP binding was detected to smooth muscle of mammary artery, with receptor density of ∼2 fmol mg–1 protein, comparable to that of other vasoactive peptides. NPR‐A immunoreactivity was localised to vascular smooth muscle cells and this was confirmed with fluorescence dual labelling. NPR‐A expression was not detected in the endothelium. Like ANP, DNP fully reversed the constrictor response to ET‐1 in endothelium intact or denuded mammary artery, with comparable nanomolar potencies.

Conclusions and Implications:

This is the first characterization of NPR‐A in human mammary artery using [125I]‐DNP and we provide evidence for the presence of receptor protein on vascular smooth muscle cells, but not endothelial cells. This implies that the observed vasodilatation is predominantly mediated via direct activation of smooth muscle NPR‐A.

British Journal of Pharmacology (2006) 149, 838–844. doi:10.1038/sj.bjp.0706924
The MC4 receptor and control of appetite
Authors: Adan R A H , Tiesjema B , Hillebrand J J G , la Fleur S E , Kas M J H , de Krom M
Published: October 2006

Mutations in the human melanocortin (MC)4 receptor have been associated with obesity, which underscores the relevance of this receptor as a drug target to treat obesity. Infusion of MC4R agonists decreases food intake, whereas inhibition of MC receptor activity by infusion of an MC receptor antagonist or with the inverse agonist AgRP results in increased food intake. This review addresses the role of the MC system in different aspects of feeding behaviour. MC4R activity affects meal size and meal choice, but not meal frequency, and the type of diet affects the efficacy of MC4R agonists to reduce food intake. The central sites involved in the different aspects of feeding behaviour that are affected by MC4R signalling are being unravelled. The paraventricular nucleus plays an important role in food intake per se, whereas MC signalling in the lateral hypothalamus is associated with the response to a high fat diet. MC4R signalling in the brainstem has been shown to affect meal size. Further genetic, behavioural and brain‐region specific studies need to clarify how the MC4R agonists affect feeding behaviour in order to determine which obese individuals would benefit most from treatment with these drugs. Application of MCR agonists in humans has already revealed side effects, such as penile erections, which may complicate introduction of these drugs in the treatment of obesity.

British Journal of Pharmacology (2006) 149, 815–827. doi:10.1038/sj.bjp.0706929
E-Business Strategy and Firm Performance: A Latent Class Assessment of the Drivers and Impediments to Success
Authors: Coltman Tim R , Devinney Timothy M , Midgley David F
Published: October 2006

Among many leading organizations, in all sectors of industry, commerce and government, there is considerable evidence of e-business being deployed to achieve strategic goals. Where this deployment has been most successful, there is a strong case that the organization has taken an integrated approach that both builds on the organization's strengths and pays careful attention to the process of change within the organization. However, in the literature most empirical work has either studied e-business strategy and performance from the perspective of strategy content – which highlights positioning and/or unique bundles of resources – or from the perspective of strategy process – which captures human influence and e-business implementation. In this study, we integrate these two perspectives to develop a more holistic understanding of the underlying drivers of e-business performance. Further, latent class modeling techniques are used to show that the variables in our study are heavily influenced by the unobservable heterogeneity across firms. Four distinct types of firms populate our data, and the relationship between performance and its underlying determinants varies greatly between them. The implication is that a single model cannot explain the relationship between environment, structure, feasibility, managerial beliefs and performance. This is critical to our understanding of e-business as it implies that there is far less homogeneity at the individual firm level than is normally assumed in the literature.
A study of Ni-based refractory alloys via anomalous scattering techniques
Authors: Tokarz Michelle L. , Bilello John C.
Published: October 2006

Anomalous x-ray scattering methods provided means to probe the local interactions of specific chemical pairs in a Ni–Nb–Sn sequence. Data near and far from the absorption edges of individual constituent atoms were obtained to calculate differential distribution functions, revealing the atomic arrangements. The compositional fluctuations throughout a typical Ni60Nb40−xSny sample is described as alternating Ni-rich and Nb-rich clusters of ∼25Å dimensions. This nonrandom distribution of atomic species may partially explain the failure of previous modeling efforts of bulk metallic glasses to explain their mechanical behavior and thermal stability.
Nonisothermal asymmetric expansion of laser induced plasmas into vacuum
Authors: Gornushkin I. B. , Shabanov S. V. , Omenetto N. , Winefordner J. D.
Published: October 2006

A theoretical model is developed that describes an asymmetric expansion of radiative, thermally anisotropic, laser induced plasmas into vacuum. The model is based on the conventional fluid dynamic equations supplemented by the equations of state and radiative transfer. The plasma is assumed to be nonviscous and nonconducting. It is proven that the self-similarity expansion law, when there is a rectangular coordinate system in which the velocity vector field components of plasma species are proportional to the corresponding coordinates, cannot hold true for generic thermally anisotropic plasmas with radiative losses. When the effects of radiative losses on the plasma expansion are neglected, a simple analytical model is obtained for fast numerical simulations of plasma dynamics. The model is shown to have analytical solutions for axially symmetric plasma shapes which explain the flip-over effect observed experimentally. Numerical calculations are performed for the silicon plasma adiabatically expanding into vacuum. The radiative properties of such plasma are investigated. It is shown that spectral line intensities and Stark shifts depend strongly on the direction in which the emission spectrum is observed. This result is relevant for improving spectroscopic methods of plasma diagnostics.
Electronic spectroscopy of NO–(Rg)x complexes (Rg=Ne,Ar) via the 4s and 3d Rydberg states
Authors: Bergeron Denis E. , Musgrave Adam , Ayles Victoria L. , Gammon Robert T. , Silber James A. E. , Wright Timothy G.
Published: October 2006

We have employed (2+1) resonance enhanced multiphoton ionization spectroscopy to investigate the 3d and 4s Rydberg states of the NO molecule when bound to the surface of Rgx clusters (Rg=rare gas). We observe that the spectra of the NO–Arx species converge in appearance as x increases, and this is discussed in terms of two Rg atoms interacting with the NO+ core, with other Rg atoms being “outside” the Rydberg orbital. We show that the interaction of each of the Rg atoms with the NO is essentially independent for the NO–Rg2 complexes: both by comparing our spectra for Rydberg states of NO–Rg and NO–Rg2, and from the results of ab initio calculations on NO+–Rg and NO+–Rg2. In addition, we discuss the disappearance of some electronic bands upon complexation in terms of Franck-Condon factors that are very sensitive to the angular coordinate. We relate our results to those of the bulk by comparing to the previously reported electronic spectroscopy of NO in both Rg matrices and He nanodroplets.
Anomalous strain relaxation behavior of Fe3O4∕MgO (100) heteroepitaxial system grown using molecular beam epitaxy
Authors: Arora S. K. , Sofin R. G. S. , Shvets I. V. , Luysberg M.
Published: October 2006

Strain relaxation studies in epitaxial magnetite (Fe3O4) thin films grown on MgO (100) substrates using high-resolution x-ray diffraction and cross-sectional transmission electron microscopy reveal that the films remain fully coherent up to a thickness of 700nm. This thickness is much greater than the critical thickness tc for strain relaxation estimated from mismatch strain. Anomalous strain relaxation behavior of Fe3O4∕MgO heteroepitaxy is attributed to the reduction in the effective stress experienced by the film due to the presence of antiphase boundaries (APBs) that enable the film to maintain coherency with the substrate at large thickness. However, the stress accommodation in the film depends upon the nature and density of the APBs.
The lowest singlet-triplet excitation energy of BN: A converged coupled cluster perspective
Authors: Karton Amir , Martin Jan M. L.
Published: October 2006

The notoriously small XΠ3−aΣ+1 excitation energy of the BN diatomic has been calculated using high-order coupled cluster methods. Convergence has been established in both the one-particle basis set and the coupled cluster expansion. Explicit inclusion of connected quadruple excitations T̂4 is required for even semiquantitative agreement with the limit value, while connected quintuple excitations T̂5 still have an effect of about 60cm−1. Still higher excitations only account for about 10cm−1. Inclusion of inner-shell correlation further reduces Te by about 60cm−1 at the CCSDT, and 85cm−1 at the CCSDTQ level. Our best estimate, Te=183±40cm−1, is in excellent agreement with earlier calculations and experiment, albeit with a smaller (and conservative) uncertainty. The dissociation energy of BN(XΠ3) is De=105.74±0.16kcal∕mol and D0=103.57±0.16kcal∕mol.
Detailed structural analysis and dielectric properties of silicon nitride film fabricated using pure nitrogen plasma generated near atmospheric pressure
Authors: Hayakawa Ryoma , Nakae Mari , Yoshimura Takeshi , Ashida Atsushi , Fujimura Norifumi , Uehara Tsuyoshi , Tagawa Masatoshi , Teraoka Yuden
Published: October 2006

A detailed structural analysis and dielectric property measurements of silicon nitride films fabricated using atmospheric pressure (AP) plasma were carried out, and the results were compared to those of nitride films fabricated using a radio frequency plasma. Using AP plasma, 1.8-nm-thick silicon nitride films composed of Si3N3.5O0.7 were obtained at nitridation temperatures ranging from 25to500°C. X-ray photoelectron spectroscopy using a monochromatic AlKα source at 1486.6eV and high-resolution Rutherford backscattering spectrometry revealed approximately 10% more nitrogen atoms corresponding to the N–Si3 bond in the film using AP plasma than those using rf plasma. In the range of 25–500°C, the nitridation temperature did not affect the leakage current densities of the films fabricated using AP plasma. Films fabricated at 25°C showed leakage current density of as low as 7×10−2A∕cm2 at 5MV∕cm. This value was one order of magnitude lower than that using rf plasma. The direct-tunneling current simulation analysis with the Wentzel-Kramers-Brillouin approximation revealed that the effective tunneling mass of holes increased due to the nitrogen atoms incorporated in the films. From deep-level transient spectroscopy, signals attributed to defects generated by plasma irradiation in the silicon substrate were not observed.
A microscopic model of electron transport in quantum dot infrared photodetectors
Authors: Vukmirović Nenad , Ikonić Zoran , Savić Ivana , Indjin Dragan , Harrison Paul
Published: October 2006

A theoretical model describing the electron transport in vertical conductivity quantum dot infrared photodetectors is presented. The carrier wave functions and energy levels were evaluated using the strain dependent eight-band k∙p Hamiltonian and used to calculate all intra- and interperiod transition rates due to interaction with phonons and electromagnetic radiation. The interaction with longitudinal acoustic phonons and electromagnetic radiation was treated perturbatively within the framework of Fermi’s golden rule, while the interaction with longitudinal optical phonons was considered taking into account their strong coupling to electrons. A system of rate equations was then formed, from which the macroscopic device output parameters such as dark current and responsivity, as well as microscopic information about carrier distribution in quantum dots and continuum states, could be extracted. The model has been applied to simulate the dark current, as well as the midinfrared photoresponse in an experimentally realized device [Chen et al., J. Appl. Phys. 89, 4558 (2001)], and a good agreement with experiment has been obtained. Being free from any fitting or phenomenological parameters, the model should be a useful tool in the design and prediction of the characteristics of the existing or other types of quantum dot infrared photodetectors.
Identification by photoluminescence and positron annihilation of vacancy and interstitial intrinsic defects in ion-implanted silicon
Authors: Harding R. , Davies G. , Tan J. , Coleman P. G. , Burrows C. P. , Wong-Leung J.
Published: October 2006

Defect centers generated in crystalline silicon by MeV Si implants have been investigated by a combination of photoluminescence, variable-energy positron annihilation measurements, depth profiling by etching, annealing studies, and the dependence on impurities. The broad 935meV photoluminescence band occurs at intrinsic interstitial complexes, the 835meV band at small vacancy clusters, and the 1062meV line at a low concentration of vacancy clusters which are possibly formed by aggregation of the 835meV centers.
Large signal circuit model of parallel-plate ferroelectric varactors
Authors: Rundqvist P. , Vorobiev A. , Kollberg E. , Gevorgian S.
Published: October 2006

A simple one port reflection method is proposed to measure the large signal permittivity and loss tangent of ferroelectric films. The microwave power levels are changed in the range from −10to17dBm at 0V dc bias. Microwave power causes two effects: (i) generation of higher order harmonics due to the dielectric nonlinearities and (ii) heating of the ferroelectric film. The harmonic generation is measured as loss since the instruments (network analyzer and LCR meter) do not detect the higher order harmonics. The heating, on the contrary, is found to cause a reduction of observed microwave losses and at higher microwave power becomes dominant, partly compensating for the loss increase caused by harmonic generation. The heating effect is substantially reduced if the applied microwave signal is pulsed. The results are used to extract parameters for a simplified large signal circuit model of the thin film parallel-plate ferroelectric varactors in the frequency range of 10–45GHz. Only a limited number of measurements are used in modeling. The model is useful for zero bias mixer (up and down converter) and harmonic generator applications of ferroelectric varactors.
Influence of dopant compounds on the storage mechanism of CaS:Eu2+,Sm3+
Authors: Weidner M. , Osvet A. , Schierning G. , Batentschuka M. , Winnackera A.
Published: October 2006

The present article demonstrates the dependence of the infrared stimulable luminescence of CaS:Eu2+;Sm3+ on the anionic partner of the used rare earth dopant compound. Subjected to two different dopant compounds (Eu2O3, Sm2O3 or EuCl3, SmCl3), discrepancies to the common model of trapping and release of the charge carriers are presented. According to temperature dependent measurements of photo- and infrared stimulated luminescence, improved models of the storage mechanism are given.
Depth profiling of strain and defects in Si∕Si1−xGex∕Si heterostructures by micro-Raman imaging
Authors: Mitani T. , Nakashima S. , Okumura H. , Ogura A.
Published: October 2006

We have reported depth and in-plane profiling of strain, Ge composition, and defects in strained-Si∕Si1−xGex∕Si heterostructures using micro-Raman imaging. Raman profiling in the depth direction was carried out with a depth resolution of ∼15nm using a small-angle beveled sample and ultraviolet (UV) excitation. Depth profiles of the Ge composition and Raman bandwidth clearly show that the defect density depends strongly on the Ge-grading rate in a compositionally graded Si1−xGex layer. The in-plane strain variation at a given depth in each layer has been evaluated. The in-plane strain variations in the Si1−xGex are closely related to clustering of misfit dislocations in the graded Si1−xGex layer. For the top strained-Si layer, two-dimensional UV-Raman images of the frequency and bandwidth of the Si band reveal that film crystallinity is correlated with the magnitude of in-plane strain. The close correlation between the frequency and bandwidth is attributed to inhomogeneous strain fields associated with misfit dislocation clusters, which induce complete relaxation of strain in constant composition Si1−xGex layers.
Crystal structure and thermoelectric properties of type-I clathrate compounds in the Ba–Ga–Ge system
Authors: Okamoto Norihiko L. , Kishida Kyosuke , Tanaka Katsushi , Inui Haruyuki
Published: October 2006

The crystal structure and thermoelectric properties of type-I clathrate compounds in the Ba–Ga–Ge system have been investigated as a function of Ga content. The solid solubility of Ga in the type-I clathrate compounds is determined to be X=16 when expressed with the formula of Ba8GaXGe46−X. As the Ga content increases, the crystal structure changes from a superlattice structure to the normal type-I clathrate structure with the transition occurring at X=3.5–5. The density of Ge vacancies in the type-I clathrate phase decreases as the Ga content increases. The absolute values of electrical resistivity and Seebeck coefficient increase, while that of lattice thermal conductivity decreases with the increase in the Ga content. The changes in electrical resistivity and Seebeck coefficient are explained in terms of the number of excess electrons, while the change in lattice thermal conductivity is explained in terms of the extent of the rattling motion of Ba atoms encapsulated in the cage structure.
Transport in room temperature gases induced by optical lattices
Authors: Shneider M. N. , Barker P. F. , Gimelshein S. F.
Published: October 2006

The coupling between nonresonant laser radiation and gas through absorption of energy and momentum from an optical lattice is examined analytically and numerically in the collisional regime. The energy and momentum depositions are studied and indicate the formation of gas jets in free space and a bulk drift in a capillary. Analytical expressions describing the energy and momentum transfer from the lattice to the gas in a collisional regime are developed and compared with the numerical predictions obtained with the direct simulation Monte Carlo method.
Current-voltage and capacitance-voltage characteristics of Sn/rhodamine-101∕n-Si and Sn/rhodamine-101∕p-Si Schottky barrier diodes
Authors: Çakar Muzaffer , Yıldırım Nezir , Karataş Şukru , Temirci Cabir , Türüt Abdulmecit
Published: October 2006

The nonpolymeric organic compound rhodamine-101 (Rh101) film on a n-type Si or p-type Si substrate has been formed by means of the evaporation process and the Sn/rhodamine-101/Si contacts have been fabricated. The Sn∕Rh101∕n-Si and Sn∕Rh101∕p-Si contacts have rectifying contact behavior with the barrier height (BH) values of 0.714 and 0.827eV, and with ideality factor values of 2.720 and 2.783 obtained from their forward bias current-voltage (I-V) characteristics at room temperature, respectively. It has been seen that the BH value of 0.827eV obtained for the Sn∕Rh101∕p-Si contact is significantly larger than BH values of the conventional Sn∕p-Si Schottky diodes and metal/interfacial layer/Si contacts. Thus, modification of the interfacial potential barrier for metal/Si diodes has been achieved using a thin interlayer of the Rh101 organic semiconductor; this has been ascribed to the fact that the Rh101 interlayer increases the effective barrier height by influencing the space charge region of Si.
Elastic properties of inverted frustums
Authors: Mon K. K.
Published: October 2006

Elastic energies of nanostructures are important. The nanostructures are often sufficiently large that Euler-Bernoulli theory (EBT) is adequate. Motivated by recent applications, we use EBT to calculate the bending profile and the scaling of the spring constant of inverted frustums with length (h) and cross sections [b(h)∼h0.3]. We find keff∼h−1.8 which differs significantly from that of a straight rod keff∼h−3 and demonstrates that the shape of the nanorods provides a mean to vary the scaling of the elastic properties.
Collisions and reactions of gaseous propanol with molten NaOH∕KOH
Authors: Castro David J. , Dragulin Sonia M. , Manning Michelle , Nathanson Gilbert M.
Published: October 2006

Molecular beam scattering experiments are used to investigate collisions of a protic molecule, deuterated 1-propanol (PrOD), with an extremely basic solvent, the 51∕49mol% NaOH∕KOH eutectic mixture. This powerful deprotonating medium readily absorbs PrOD from the gas phase. Nearly all PrOD molecules that thermalize at the surface of the melt enter the liquid and dissolve for long times, most likely residing as PrO− after deprotonation by OH−. The PrO− solvation time is controlled by dissolved H2O, which reprotonates the anion and liberates D→H exchanged PrOH. We find no evidence for decomposition of the alcohol; at the 463K temperature of the experiments, the hydroxide solution appears to store propanol reversibly.
Influence of sintering temperature, pressing, and conformal coatings on electron diffusion in electrophoretically deposited porous TiO2
Authors: Ofir A. , Dittrich Th. , Tirosh S. , Grinis L. , Zaban A.
Published: October 2006

The electrophoretic deposition of nanoporous TiO2 layers allows us to investigate separately the influence of sintering temperature, porosity, and conformal surface coatings on the effective diffusion coefficient (Deff) of excess electrons in porous layers. Photocurrent transients were measured to obtain Deff in nanoporous TiO2 layers immersed in aqueous electrolyte. The applied treatments control parameters such as the contact between interconnected nanoparticles, the coordination of nanoparticles in the porous network, and the surface passivation of TiO2 nanoparticles. The hierarchy of the different factors for transport optimization in porous TiO2 is discussed. Under fixed geometry of the nanoporous network, trapping on surface states can strongly limit electron diffusion in porous TiO2.
Molecular dynamics simulations of water droplets on polymer surfaces
Authors: Hirvi Janne T. , Pakkanen Tapani A.
Published: October 2006

Molecular dynamics simulations were used to study the wetting of polymer surfaces with water. Contact angles of water droplets on crystalline and two amorphous polyethylene (PE) and poly(vinyl chloride) (PVC) surfaces were extracted from atomistic simulations. Crystalline surfaces were produced by duplicating the unit cell of an experimental crystal structure, and amorphous surfaces by pressing the bulk polymer step by step at elevated temperature between two repulsive grid surfaces to a target density. Different-sized water droplets on the crystalline PE surface revealed a slightly positive line tension on the order of 10−12–10−11N, whereas droplets on crystalline PVC did not yield a definite line tension. Microscopic contact angles produced by the simple point charge (SPC) water model were mostly a few degrees smaller than those produced by the extended SPC model, which, as the model with lowest bulk energy, presents an upper boundary for contact angles. The macroscopic contact angle for the SPC model was 94° on crystalline PVC and 113° on crystalline PE. Amorphicity of the surface increased the water contact angle on PE but decreased it on PVC, for both water models. If the simulated contact angles on crystalline and amorphous surfaces are combined in proportion to the crystallinity of the polymer in question, simulated values in relatively good agreement with measured values are obtained.
Energy band structure and spectral gain characteristics of dilute-nitride zinc blende InGaNAs quantum wells embedded in GaAs and GaNAs barriers
Authors: Fu Y. , Wei Y.-Q. , Wang X.-D. , Sadeghi M. , Wang S.-M. , Larsson A.
Published: October 2006

The spectral gain characteristics of dilute-nitride zinc blende InxGa1−xNyAs1−y quantum wells embedded in GaNy1As1−y1 barriers have been investigated experimentally and theoretically. Two samples, both with the gain peak at 1300nm, were studied for comparison. One has a high nitrogen concentration in the quantum well with the surrounding barriers being pure GaAs. The other has a lower and uniform nitrogen concentration in the quantum well and the barriers (GaNAs barriers). Measurements show the redshift of the gain peak induced by the incorporation of nitrogen and difference in the spectral gain characteristics. The energy band structures and spectral gain characteristics are analyzed theoretically using the standard eight-band k∙p theory. It is shown that the introduction of nitrogen atoms in the GaAs barriers reduces the barrier height for the central quantum well so that the energy sublevels in the conduction band becomes condensed. The condensation of the conduction-band energy sublevels reduces the peak gain and makes the gain spectrum narrower, in agreement with measurements.
Microwave diagnostics of laser-induced avalanche ionization in air
Authors: Zhang Zhili , Shneider Mikhail N. , Miles Richard B.
Published: October 2006

This work presents a simplified model of microwave scattering during the avalanche ionization stage of laser breakdown and corresponding experimental results of microwave scattering from laser breakdown in room air. The model assumes and measurements confirm that the breakdown regime can be viewed as a point dipole scatterer of the microwave radiation and thus directly related to the time evolving number of electrons. The delay between the laser pulse and the rise of the microwave scattering signal is a direct measure of the avalanche ionization process.
Does equilibrium polymerization describe the dynamic heterogeneity of glass-forming liquids?
Authors: Douglas Jack F. , Dudowicz Jacek , Freed Karl F.
Published: October 2006

A significant body of evidence indicates that particles with excessively high or low mobility relative to Brownian particles form in dynamic equilibrium in glass-forming liquids. We examine whether these “dynamic heterogeneities” can be identified with a kind of equilibrium polymerization. This correspondence is first checked by demonstrating the presence of a striking resemblance between the temperature dependences of the configurational entropy sc in both the theory of equilibrium polymerization and the generalized entropy theory of glass formation in polymer melts. Moreover, the multiple characteristic temperatures of glass formation are also shown to have analogs in the thermodynamics of equilibrium polymerization, supporting the contention that both processes are varieties of rounded thermodynamic transitions. We also find that the average cluster mass (or degree of polymerization) varies in nearly inverse proportionality to sc. This inverse relation accords with the basic hypothesis of Adam-Gibbs that the number of particles in the cooperatively rearranging regions (CRR) of glass-forming liquids scales inversely to sc of the fluid. Our identification of the CRR with equilibrium polymers is further supported by simulations for a variety of glass-forming liquids that verify the existence of stringlike or polymeric clusters exhibiting collective particle motion. Moreover, these dynamical clusters have an exponential length distribution, and the average “string” length grows upon cooling according to the predictions of equilibrium polymerization theory. The observed scale of dynamic heterogeneity in glass-forming liquids is found to be consistent with this type of self-assembly process. Both experiments and simulations have revealed remarkable similarities between the dynamical properties of self-assembling and glass-forming liquids, suggesting that the development of a theory for the dynamics of self-assembling fluids will also enhance our understanding of relaxation in glass-forming liquids.
Electric-field-induced dielectric anomalies and optical birefringence in Pb(Zn1∕3Nb2∕3)1−xTixO3 (x=0.10) single crystal
Authors: Tu C.-S. , Wang F.-T. , Chien R. R. , Schmidt V. H. , Lim L.-C.
Published: October 2006

This work aims to study thermal stability, frequency response, and refractive indices in a (001)-cut Pb(Zn1∕3Nb2∕3)0.90Ti0.10O3 (PZNT10%) crystal before and after an electric (E)-field poling, which are important for piezoelectric and optical uses. Dielectric permittivities have been measured as functions of temperature, frequency, and poling strength. The dielectric absorption reveals a broad dipolar relaxation in the region of 260–310K in the unpoled sample. Piezoelectric resonances were observed in the poled sample and show significant changes while phase transitions are taking place. The unpoled crystal shows almost no birefringence, indicating that the structure averaged over the optically anisotropic ferroelectric domains is optically isotropic. Birefringence appears after an E-field poling and shows a “negative” uniaxial distortion. The Cauchy equations for ordinary no and extraordinary ne refractive indices were determined between 0.45 and 1.4μm. However, the phase-matching criterion for second harmonic generation was not found.
Semianalytical model of tunneling in nanocrystal-based memories
Authors: Leriche B. , Leroy Y. , Cordan A. S.
Published: October 2006

The purpose of this paper is to study single electron charging of a floating gate composed of nanocrystals in a metal-oxide-semiconductor transistor. We present a three-dimensional model of electron tunneling into quantum islands that are spherical in shape. This model can be numerically solved through a two-dimensional finite element approach. In this way, extensive and accurate numerical experimentations can be carried out due to the reduced computer time cost. The curves of tunneling time versus bias voltage exhibit complex serrated shapes, related to both the energy subbands of the channel and the energy states of the nanocrystal. The results are discussed for different channel doping densities.