Chain conformation in polymer nanocomposites with uniformly dispersed nanoparticles.

The effect of nanoparticles (NP) on chain dimensions in polymer melts has been the source of considerable theoretical and experimental controversy. We exploit our ability to ensure a spatially uniform dispersion of 13 nm silica NPs miscible in polystyrene melts, together with neutron scattering, x-ray scattering, and transmission electron microscopy, to show that there is no measurable change in the polymer size in miscible mixtures, regardless of the relative sizes of the chains and the nanoparticles, and for NP loadings as high as 32.7 vol%. Our results provide a firm basis from which to understand the properties of polymer nanocomposites.

The 2010 Mw 8.8 Maule megathrust earthquake of Central Chile, monitored by GPS.

Large earthquakes produce crustal deformation that can be quantified by geodetic measurements, allowing for the determination of the slip distribution on the fault. We used data from Global Positioning System (GPS) networks in Central Chile to infer the static deformation and the kinematics of the 2010 moment magnitude (M(w)) 8.8 Maule megathrust earthquake. From elastic modeling, we found a total rupture length of ~500 kilometers where slip (up to 15 meters) concentrated on two main asperities situated on both sides of the epicenter. We found that rupture reached shallow depths, probably extending up to the trench. Resolvable afterslip occurred in regions of low coseismic slip. The low-frequency hypocenter is relocated 40 kilometers southwest of initial estimates. Rupture propagated bilaterally at about 3.1 kilometers per second, with possible but not fully resolved velocity variations.

Excitons in carbon nanotubes with broken time-reversal symmetry.

Near-infrared magneto-optical spectroscopy of single-walled carbon nanotubes reveals two absorption peaks with an equal strength at high magnetic fields (>55 T). We show that the peak separation is determined by the Aharonov-Bohm phase due to the tube-threading magnetic flux, which breaks the time-reversal symmetry and lifts the valley degeneracy. This field-induced symmetry breaking thus overcomes the Coulomb-induced intervalley mixing which is predicted to make the lowest exciton state optically inactive (or dark).

Space geodetic evidence for rapid strain rates in the New Madrid seismic zone of central USA.

In the winter of 1811-1812, near the town of New Madrid in the central United States and more than 2,000 km from the nearest plate boundary, three earthquakes within three months shook the entire eastern half of the country and liquefied the ground over distances far greater than any historic earthquake in North America. The origin and modern significance of these earthquakes, however, is highly contentious. Geological evidence demonstrates that liquefaction due to strong ground shaking, similar in scale to that generated by the New Madrid earthquakes, has occurred at least three and possibly four times in the past 2,000 years (refs 4-6), consistent with recurrence statistics derived from regional seismicity. Here we show direct evidence for rapid strain rates in the area determined from a continuously operated global positioning system (GPS) network. Rates of strain are of the order of 10(-7) per year, comparable in magnitude to those across active plate boundaries, and are consistent with known active faults within the region. These results have significant implications for the definition of seismic hazard and for processes that drive intraplate seismicity.

Stability of high-density one-dimensional excitons in carbon nanotubes under high laser excitation.

Through ultrafast pump-probe spectroscopy with intense pump pulses and a wide continuum probe, we show that interband exciton peaks in single-walled carbon nanotubes (SWNTs) are extremely stable under high laser excitations. Estimates of the initial densities of excitons from the excitation conditions, combined with recent theoretical calculations of exciton Bohr radii for SWNTs, suggest that their positions do not change at all even near the Mott density. In addition, we found that the presence of lowest-subband excitons broadens all absorption peaks, including those in the second-subband range, which provides a consistent explanation for the complex spectral dependence of pump-probe signals reported for SWNTs.

Introduction to the DAPPLE Air Pollution Project.

The Dispersion of Air Pollution and its Penetration into the Local Environment (DAPPLE) project brings together a multidisciplinary research group that is undertaking field measurements, wind tunnel modelling and computer simulations in order to provide better understanding of the physical processes affecting street and neighbourhood-scale flow of air, traffic and people, and their corresponding interactions with the dispersion of pollutants at street canyon intersections. The street canyon intersection is of interest as it provides the basic case study to demonstrate most of the factors that will apply in a wide range of urban situations. The aims of this paper are to introduce the background of the DAPPLE project, the study design and methodology for data collection, some preliminary results from the first field campaign in central London (28 April-24 May 2003) and the future for this work. Updated information and contact details are available on the web site at http://www.dapple.org.uk.

Interband recombination dynamics in resonantly excited single-walled carbon nanotubes.

Wavelength-dependent pump-probe spectroscopy of micelle-suspended single-walled carbon nanotubes reveals two-component dynamics. The slow component (5-20 ps), which has not been observed previously, is resonantly enhanced whenever the pump photon energy coincides with an absorption peak and we attribute it to interband carrier recombination, whereas we interpret the always-present fast component (0.3-1.2 ps) as intraband carrier relaxation in nonresonantly excited nanotubes. The slow component decreases drastically with decreasing pH (or increasing H+ doping), especially in large-diameter tubes. This can be explained as a consequence of the disappearance of absorption peaks at high doping due to the entrance of the Fermi energy into the valence band, i.e., a 1D manifestation of the Burstein-Moss effect.

Similarity solution of temperature structure functions in decaying homogeneous isotropic turbulence.

An equilibrium similarity analysis is applied to the transport equation for <(deltatheta)(2)>, the second-order temperature structure function, for decaying homogeneous isotropic turbulence. A possible solution is that the temperature variance decays as x(n), and that the characteristic length scale, identifiable with the Taylor microscale lambda, or equivalently the Corrsin microscale lambda(theta), varies as x(1/2). The turbulent Reynolds and Péclet numbers decay as x((m+1)/2) when m<-1, where m is the exponent which characterizes the decay of the turbulent energy , viz., approximately x(m). Measurements downstream of a grid-heated mandoline combination show that, like <(deltaq)(2)>, <(deltatheta)(2)> satisfies similarity approximately over a significant range of scales r, when lambda, lambda(theta), , and are used as the normalizing scales. This approximate similarity is exploited to calculate the third-order structure functions. Satisfactory agreement is found between measured and calculated distributions of and , where deltau is the longitudinal velocity increment.

The role of surfactant adsorption during ultrasonication in the dispersion of single-walled carbon nanotubes.

The ionic surfactant-assisted dispersion of single-walled carbon nanotubes in aqueous solution has been studied by Raman and fluorescent spectroscopy during ultrasonic processing. During the process, an equilibrium is established between free individuals and aggregates or bundles that limits the concentration of the former that is possible. This equilibrium is a function of free sodium dodecyl sulfate concentration. At surfactant concentrations below this value, fluorescence is shifted to a lower energy due to an increase in micropolarity from water association at the nanotube surface. The mechanism of dispersion is postulated as the formation of gaps or spaces at the bundle ends in the high shear environment of the ultrasonicated solution. Surfactant adsorption and diffusion then propagate this space along the bundle length, thereby separating the individual nanotube. The former is found to be controlling, with the use of a derived kinetic model for the dispersion process and extraction of the characteristic rate of nanotube isolation.

Thermoelectric power of p-doped single-wall carbon nanotubes and the role of phonon drag.

We measured thermoelectric power S of bulk single-wall carbon nanotube materials p doped with acids. In contrast to oxygen-exposed or degassed samples, S is very small at the lowest temperatures, increases superlinearly above a characteristic and sample-dependent T, and then levels off. We attribute this unusual behavior to 1D phonon drag, in which the depression of the Fermi energy cuts off electron-phonon scattering at temperatures below a characteristic T0. This idea is supported by a model calculation in which the low temperature behavior of phonon drag is specifically related to the one-dimensional character of the electronic spectrum.

Covalent sidewall functionalization of single wall carbon nanotubes.

Alkyllithium reagents may be used to attach alkyl groups to the sidewalls of fluoro nanotubes. Thermal gravimetric analysis combined with UV-vis-Nir spectroscopy has been used to provide a quantitative measure of the degree of functionalization. SWNTs prepared using the HiPco process exhibit a higher degree of alkylation than SWNTs from the laser-oven method, indicating that the smaller diameter fluoro tubes are alkylated more readily. The spectral signature of the pristine SWNTs can be regenerated when the alkylated SWNTs are heated in Ar at 500 degrees C, demonstrating that dealkylation occurs at this temperature. TGA-MS analysis using a sample of n-butylated h-SWNTs showed that 1-butene and n-butane are formed during thermolysis.

Raman-active modes of single-walled carbon nanotubes derived from the gas-phase decomposition of CO (HiPco process).

Here we report Raman scattering studies of ropes of Single-walled carbon nanotubes (SWNTs) grown by a high CO pressure process. Five samples from five different batches were studied as a function of excitation wavelength. Three of these samples exhibited Raman spectra similar to that found for SWNTs made by pulsed laser vaporization of arc-discharge methods. The other two samples were found by Raman scattering to contain a significant fraction of tubes with diameter < 1.0 nm. These samples exhibited unusual spectra that, however, can be well understood within the existing models for the electronic and phononic states in SWNTs. Spectra recorded with 1064 nm for the sample having a significant fraction of smaller diameter tubes shows strong modes present between 500 and 1200 cm-1. We suggest these modes arise due to the enhancement of Raman cross-section for small diameter tubes.

Oxygen-containing functional groups on single-wall carbon nanotubes: NEXAFS and vibrational spectroscopic studies.

Single-walled nanotubes (SWNTs) produced by plasma laser vaporization (PLV) and containing oxidized surface functional groups have been studied for the first time with NEXAFS. Comparisons are made to SWNTs made by catalytic synthesis over Fe particles in high-pressure CO, called HiPco material. The results indicate that the acid purification and cutting of single-walled nanotubes with either HNO3/H2SO4 or H2O2/H2SO4 mixtures produces the oxidized groups (O/C = 5.5-6.7%), which exhibit both pi*(CO) and sigma*(CO) C K-edge NEXAFS resonances. This indicates that both carbonyl (C=O) and ether C-O-C functionalities are present. Upon heating in a vacuum to 500-600 K, the pi*(CO) resonances are observed to decrease in intensity; on heating to 1073 K, the sigma*(CO) resonances disappear as the C-O-C functional groups are decomposed. Raman spectral measurements indicate that the basic tubular structure of the SWNTs is not perturbed by heating to 1073 K, based on the invariance of the ring breathing modes upon heating. The NEXAFS studies agree well with infrared studies which show that carboxylic acid groups are thermally destroyed first, followed by the more difficult destruction of ether and quinone groups. Single-walled nanotubes produced by the HiPco process, and not treated with oxidizing acids, exhibit an O/C ratio of 1.9% and do not exhibit either pi*(CO) or sigma*(CO) resonances at the detection limit of NEXAFS. It is shown that heating (to 1073 K) of the PLV-SWNTs containing the functional groups produces C K-edge NEXAFS spectra very similar to those seen for the HiPco material. The NEXAFS spectra are calibrated against spectra measured for a number of fused-ring aromatic hydrocarbon molecules containing various types of oxidized functional groups present on the oxidized SWNTs.

Two-dimensional imaging of electronic wavefunctions in carbon nanotubes.

The drive towards the development of molecular electronics is placing increasing demands on the level of control that must be exerted on the electronic structure of materials. Proposed device architectures ultimately rely on tuning the interactions between individual electronic states, which amounts to controlling the detailed spatial structure of the electronic wavefunctions in the constituent molecules. Few experimental tools are available to probe this spatial structure directly, and the shapes of molecular wavefunctions are usually only known from theoretical investigations. Here we present scanning tunnelling spectroscopy measurements of the two-dimensional structure of individual wavefunctions in metallic single-walled carbon nanotubes; these measurements reveal spatial patterns that can be directly understood from the electronic structure of a single graphite sheet, and which represent an elegant illustration of Bloch's theorem at the level of individual wavefunctions. We also observe energy-dependent interference patterns in the wavefunctions and exploit these to directly measure the linear electronic dispersion relation of the metallic single-walled carbon nanotube.

Functionalization of carbon nanotubes by electrochemical reduction of aryl diazonium salts: a bucky paper electrode.

Small-diameter (ca. 0.7 nm) single-wall carbon nanotubes are predicted to display enhanced reactivity relative to larger-diameter nanotubes due to increased curvature strain. The derivatization of these small-diameter nanotubes via electrochemical reduction of a variety of aryl diazonium salts is described. The estimated degree of functionalization is as high as one out of every 20 carbons in the nanotubes bearing a functionalized moiety. The functionalizing moieties can be removed by heating in an argon atmosphere. Nanotubes derivatized with a 4-tert-butylbenzene moiety were found to possess significantly improved solubility in organic solvents. Functionalization of the nanotubes with a molecular system that has exhibited switching and memory behavior is shown. This represents the marriage of wire-like nanotubes with molecular electronic devices.

Final analysis of the ECOG I-COPA trial (E6484) in patients with non-Hodgkin's lymphoma treated with interferon alfa (IFN-alpha2a) plus an anthracycline-based induction regimen.

The Eastern Cooperative Oncology Group (ECOG) performed a prospectively randomized study (E6484) evaluating the use of interferon alfa 2a (IFN-alpha2a) in patients with aggressive low-grade or with intermediate-grade non-Hodgkin's lymphoma (NHL) accruing close to 300 patients between 1985 and 1988. Patients were eligible for study if they had bulky or symptomatic low-grade lymphoma or defined intermediate-grade subtypes. Of 291 patients enrolled, 249 were eligible for analysis. All patients were randomized to receive a four-drug cytotoxic chemotherapy regimen including cyclophosphamide, doxorubicin, vincristine and prednisone in 4-week cycles with or without IFN-alpha2a in addition (COPA vs I-COPA). Treatment was given for up to 8-10 months. This report, at a time when the median follow-up among survivors has reached 12 years, updates the analysis of time to treatment failure (TTF), duration of disease-free survival (DFS), and overall survival. Patients randomized to receive IFN-alpha2a had a prolonged TTF (P= 0.008; median 2.4 vs 1.6 years). DFS for those patients who had complete responses was also longer if IFN-alpha2a had been given (P = 0.035; median 2.7 vs 1.8 years). There was a clinically but not a statistically significant prolongation of overall survival by IFN-alpha2a (P= 0.107; median 7.8 vs 5.7 years). There were fewer deaths over time due to lymphoma in patients receiving IFN-alpha2a (67 vs 80 deaths). A subset analysis, based on disease histology (low-grade, follicular, intermediate-grade), revealed a significant prolongation of TTF in patients receiving IFN-alpha2a with either low-grade (P = 0.002; median 2.4 vs 1.6 years) or follicular (P= 0.01; median 2.5 vs 1.7 years) NHL but not intermediate grade (P = 0.622; median 2.3 vs 1.6 years) NHL. This analysis, performed approximately 12 years after closure of the study to accrual, supports the addition of interferon alfa to an induction cytotoxic chemotherapy regimen including cyclophosphamide and doxorubicin in the treatment of follicular NHL.

Anomalous scaling of velocity and temperature structure functions.

Scaling-range power-law exponents of velocity and temperature structure functions are examined through the dimensional analysis framework of the refined similarity hypotheses using measurements in a variety of turbulent flows and Reynolds numbers. The resulting magnitude of the scaling exponent associated with the locally averaged energy dissipation rate epsilon(r) is always larger than 2/3, whereas the exponent for the locally averaged temperature dissipation rate chi(r) is always smaller than 2/3. While the epsilon(r) exponent may be reconciled with the exponent of the velocity structure function, the distributions of the chi(r) and temperature structure function exponents are inherently different.

Allopurinol: intravenous use for prevention and treatment of hyperuricemia.

PURPOSE: To tabulate data obtained over a 21-year period to determine the efficacy and safety of an intravenous (IV) allopurinol preparation. PATIENTS AND METHODS: IV allopurinol was provided on a compassionate plea basis to patients of any age in whom xanthine oxidase inhibitor therapy was indicated as an adjunct to chemotherapy and for whom oral intake was restricted. Three hundred twenty-seven investigators at multiple hospitals in the United States treated 1,172 patients with IV allopurinol. The vast majority of these patients had a malignancy and were in danger of developing tumor lysis syndrome (TLS) and subsequent acute uric acid nephropathy (AUAN) and were unable to take oral allopurinol. Data referable to the time period of IV allopurinol administration were collected, collated, and analyzed retrospectively. There was no randomization. RESULTS: In patients initiating treatment for an elevated serum uric acid (SUA), the SUA normalized or improved in 87% of adult patients and normalized or improved in 95% of pediatric patients. IV allopurinol, administered prophylactically to patients at high risk of developing hyperuricemia and TLS, prevented an increase in SUA levels in 93% of adults and 92% of children. Toxicities caused by IV allopurinol were minimal and consisted of 10 instances of mild to moderate skin or allergic reactions. CONCLUSION: IV allopurinol is as efficacious and safe as oral allopurinol and will be of significant benefit to patients at risk of TLS and AUAN and unable to take oral medication.