bluuebunny/crossref_metadata_2025 huggingface dataset:
Growth assessment in tropical trees: large daily diameter fluctuations and their concealment by dendrometer bands
Authors: Sheil Douglas
Published: October 2003

Tree stems contract and expand as stem water is depleted and replaced. Band-dendrometer studies suggest that such daily changes are small (<0.2 mm diameter), and they are ignored in most growth measurements. However, several studies using other approaches note larger changes (even >1 cm diameter), suggesting that significant biases are possible. An exploratory study examined the pattern and magnitude of daily stem changes and whether commercial band-dendrometers were able to reveal them. A method involving multiple precision measurements on eight trees in a Bornean hill dipterocarp forest revealed daily shrinkage and expansion of girth of around 1 mm. Fluctuations were greater in bright weather. Band-dendrometers detected these changes but revealed less than a tenth of their magnitude. An analytical model for dendrometer error is presented that predicts how measurement biases can be reduced. Tropical trees can fluctuate appreciably in stem diameter over the day. These reversible changes are of sufficient magnitude to merit concern in growth studies. Influential biases seem especially likely when measurement intervals are short and involve systematic differences in timing and weather. Further study is required to gauge the more general influence of these measurement problems.
Early regeneration and growth dynamics of Populus tremuloides suckers in relation to fire severity
Authors: Wang G. Geoff
Published: October 2003

Four boreal mixedwood stands burned by the 1999 Black River wildfire in southeastern Manitoba were sampled to determine the effect of fire severity on density and diameter and height growth of trembling aspen (Populus tremuloides Michx.) suckers during the first three postfire years. Analysis of covariance, using prefire aspen basal area as the covariate, indicated that fire severity significantly affected postfire aspen sucker density, with significantly lower density found on severely burned plots. Changes in aspen sucker density over the three postfire years depended on fire severity, with significant changes observed only on scorched and lightly burned plots. Sucker mortality was positively related to the initial sucker density, with more than 80% of the total variance being explained. Fire severity significantly affected the growth of dominant aspen suckers in the first, but not the second and the third, postfire years. The first year of growth initially increased and then remained stable with the increase in density, while the second and third years of growth were not affected by density. Since fire severity within and (or) among burned stands is inherently heterogeneous, the effect of fire severity must be taken into account in predicting postfire density and growth of aspen suckers.
Growth and nutrient uptake by birch and maple seedlings on soil with patchy or homogeneous distribution of organic matter
Authors: van Vuuren Margret MI , Muir Adrianna A , Orians Colin M
Published: October 2003

We compare responses to soil heterogeneity of red maple (Acer rubrum L.) and gray birch (Betula pop ulifolia Marsh.). Seedlings were grown with root systems split between two pots with soil: (i) without additional organic matter or nutrients ("no-addition" treatment), (ii) with additional organic matter and nutrients distributed evenly throughout the soil ("mixed" treatment), and (iii) with additional organic matter and nutrients concentrated in one pot ("patch" treatment). Compared with the no-addition treatment, mixed and patch treatments resulted in taller plants, and greater leaf and total plant dry masses for birch, while growth of maple was mostly unaffected. Birch root biomass was significantly increased in the organic patch. Specific root length of fine roots (<1 mm diameter) in the organic patch was twice as large for birch than for maple. Total plant biomass and N and P contents did not differ between mixed and patch treatments, possibly because the contrast between N and P concentrations between patch and non-patch soil was too small. In all treatments, birches took up more N than maples. In addition, the faster localized root growth and larger specific root length indicate a greater potential for birch than for maple to exploit heterogeneous soils.
On the Anyon Description of the Laughlin Hole States
Authors: Kjønsberg Heidi , Leinaas Jon Magne
Published: October 2003

We examine the anyon representation of the Laughlin quasiholes, in particular the one-dimensional, algebraic aspects of the representation. For the cases of one and two quasiholes an explicit mapping to anyon systems is given, and the connection between the hole-states and coherent states of the fundamental algebras of observables is examined. The quasielectron case is discussed more briefly, and some remaining questions are pointed out.
Form Factors for Exclusive Semileptonic B Decays
Authors: Kim C. S. , Kim Jae Kwan , Kim Yeong Gyun , Lee Kang Young
Published: October 2003

We investigate the form factors for exclusive semileptonic decays of B meson to D, D*, based on the parton picture and helped by the results of the HQET. We obtain the numerical results for the slope of the Isgur–Wise function, which is consistent with the experimental results, and we extract the dependence of hadronic form factors on q2 by varying the input heavy quark fragmentation function without the nearest pole dominance ansätze.
Fermionic Matrix Models
Authors: Semenoff Gordon W. , Szabo Richard J.
Published: October 2003

We review a class of matrix models whose degrees of freedom are matrices with anti-commuting elements. We discuss the properties of the adjoint fermion one-matrix, two-matrix and gauge-invariant D-dimensional matrix models at large N and compare them with their bosonic counterparts, which are the more familiar Hermitian matrix models. We derive and solve the complete sets of loop equations for the correlators of these models and use these equations to examine critical behavior. The topological large N expansions are also constructed and their relation to other aspects of modern string theory, such as integrable hierarchies, is discussed. We use these connections to discuss the applications of these matrix models to string theory and induced gauge theories. We argue that as such the fermionic matrix models may provide a novel generalization of the discretized random surface representation of quantum gravity in which the genus sum alternates and the sums over genera for correlators have better convergence properties than their Hermitian counterparts. We discuss the use of adjoint fermions instead of adjoint scalars to study induced gauge theories. We also discuss two classes of dimensionally reduced models, a fermionic vector model and a supersymmetric matrix model, and discuss their applications to the branched polymer phase of string theories in target space dimensions D > 1 and also to the meander problem.
Gauge Dressing of 2D Field Theories
Authors: Kogan Ian I. , Lewis Alex , Soloviev Oleg A.
Published: October 2003

By using the gauge Ward identities, we study correlation functions of gauged WZNW models. We show that the gauge dressing of the correlation functions can be taken into account as a solution of the Knizhnik–Zamolodchikov equation. Our method is analogous to the analysis of the gravitational dressing of 2D field theories.
Coulomb Gauge Quantization and Renormalization of the Chern–Simons Theory Coupled to Fermions
Authors: Fleck M. , Foerster A. , Girotti H. O. , Gomes M. , Nascimento J. R. S. , da Silva A. J.
Published: October 2003

We study the quantization and the one-loop renormalization of the model resulting from the coupling of charged fermions with a Chern–Simons field, in the Coulomb gauge. A proof of the Lorentz covariance of the physical quantities follows after establishing the Dirac–Schwinger algebra for the Poincaré densities and the transformation properties of the fields under the Poincaré group. The Coulomb gauge one-loop renormalization program is, afterwards, implemented. The noncovariant form of the one-loop fermion propagator, Chern–Simons field propagator and the vertex are explicitly obtained. Finally, the electron anomalous magnetic moment is calculated stressing that, due to the peculiarities of the Coulomb gauge, the contributions from the self-energy diagrams turn out to be essential.
The Electromagnetic and Proca Fields Revisited: A Unified Quantization
Authors: Aldaya Víctor , Calixto Manuel , Navarro Miguel
Published: October 2003

Quantizing the electromagnetic field with a group formalism faces the difficulty of how to turn the traditional gauge transformation of the vector potential, Aμ(x) → Aμ(x) + ∂μ φ (x), into a group law. In this paper, it is shown that the problem can be solved by looking at gauge transformations in a slightly different manner which, in addition, does not require introducing any BRST-like parameter. This gauge transformation does not appear explicitly in the group law of the symmetry but rather as the trajectories associated with generalized equations of motion generated by vector fields with null Noether invariants. In the new approach the parameters of the local group, U (1)(x,t), acquire dynamical content outside the photon mass shell, a fact which also allows a unified quantization of both the electromagnetic and Proca fields.
CP Violation in SU(3) × U(1) Electroweak Model
Authors: Lee Tae Hoon , Hwang Dae Sung
Published: October 2003

We study the charged and the neutral current interactions of quarks in an SU (3)L × U (1)X electroweak model. Based on the assumption that u-type quarks coincide with their mass eigenstates, we obtain a new mixing angle θ′ and another CP violating phase δ′ in the extra heavy quark sector besides the usual Kobayashi–Maskawa mixing matrix. This new phase δ′ does not effect a change in the mass matrix elements of the [Formula: see text] systems when θ′ is small, but extra heavy quarks and gauge bosons give rise to additional contribution to the real part of the off-diagonal mass matrix elements and then the CP violation parameter ε is modified. By requiring that the tree level FCNC does not have an important effect on the [Formula: see text] and [Formula: see text] mixings in this model, we obtain a new lower bound on the mass of the extra heavy neutral gauge boson as 1.8 TeV.
Identities in Representations of the Hecke Algebra
Authors: Loesch S. , Zhou Y.-K. , Zuber J.-B.
Published: October 2003

New identities on traces of representations of the Hecke algebra on the spaces of paths on graphs are presented. These identities are relevant in the computation of partition functions with fixed boundary conditions and of two-point correlation functions in a class of lattice models. They might also help to determine the Boltzmann weights of these (allegedly) integrable models.
Fine Tuning Renormalization and Two-Particle States in Nonrelativistic Four-Fermion Model
Authors: Vall A. N. , Korenblit S. E. , Leviant V. M. , Sinitskaya A. V. , Tanaev A. B.
Published: October 2003

Exact solutions of two-particle eigenvalue problems for nonrelativistic four-fermion interaction are obtained. Appearance of Goldstone mode is found. The connection between a renormalization procedure and construction of self-adjoint extensions is revealed.
Some Remarks on High Derivative Quantum Gravity
Authors: Asorey M. , López J. L. , Shapiro I. L.
Published: October 2003

We analyze the perturbative implications of the most general high derivative approach to quantum gravity based on a diffeomorphism-invariant local action. In particular, we consider the superrenormalizable case with a large number of metric derivatives in the action. The structure of ultraviolet divergences is analyzed in some detail. We show that they are independent of the gauge-fixing condition and the choice of field reparametrization. The cosmological counterterm is shown to vanish under certain parameter conditions. We elaborate on the unitarity problem of high derivative approaches and the distribution of masses of unphysical ghosts. We also discuss the properties of the low energy regime and explore the possibility of having a multiscale gravity with different scaling regimes compatible with Einstein gravity at low energies. Finally, we show that the ultraviolet scaling of matter theories is not affected by the quantum corrections of high derivative gravity. As a consequence, asymptotic freedom is stable under those quantum gravity corrections.
Integration Over a Generic Algebra
Authors: Casalbuoni R.
Published: October 2003

In this paper we consider the problem of quantizing theories defined over configuration spaces described by noncommuting parameters. If one tries to do that by generalizing the path-integral formalism, the first problem one has to deal with is the definition of integral over these generalized configuration spaces. This is the problem we state and solve in the present work, by constructing an explicit algorithm for the integration over a generic algebra. The general conditions a given algebra has to satisfy in order to admit our integration are not yet fully understood, but many examples are discussed in order to illustrate our construction.
Congruences on the Lattice of Pseudovarieties of Finite Semigroups
Authors: Auinger K. , Hall T. E. , Reilly N. R. , Zhang S.
Published: October 2003

As a step in a study of the lattice ℒ(ℱ) of pseudovarieties of finite semigroups that attempts to take full advantage of the underlying lattice structure, a family of complete congruences is introduced on ℒ(ℱ). Such congruences provide a framework from which to study ℒ(ℱ) both locally and globally. Each is associated with a mapping of the form [Formula: see text] for some special class [Formula: see text] of finite semigroups. In some instances the class is itself a pseudovariety while in others the class will be defined in terms of certain congruences associated with Green's relations. The basic properties of these complete congruences are presented and some relations between certain operators associated with these congruences are obtained.
Free Profinite ℛ-Trivial Monoids
Authors: Almeida J. , Weil P.
Published: October 2003

This article is concerned with the structure of semigroups of implicit operations on R, the pseudovariety of all ℛ-trivial semigroups. We give two complementary descriptions for these semigroups: first by means of labeled ordinals, and second by means of labeled infinite trees of finite depth. In the first representation, the product of implicit operations has a simple characterization. In the second one, the topology on implicit operations is best visible. A similar study is conducted for the implicit operations on DRG, the non-aperiodic analogue of R. This leads to a description of the corresponding variety of recognizable languages and to the computation of certain joins of pseudovarieties.
Tutorial on Optical Parametric Processes and Devices
Authors: Tang C. L.
Published: October 2003

Progresses in nonlinear optical materials research and laser pump source development have led to rapid advances in many areas of optical parametric device technology in recent years. One particularly active area has been broadly tunable femtosecond sources. This tutorial begins with a review of the fundamentals of parametric processes. It is followed by a brief review of some of the more recent advances in femtosecond optical parametric oscillators, covering the spectral range from the visible to the mid-infrared.
Topography and Temporal Evolution of Hypoxic Viable Tissue Identified by
18
F-Fluoromisonidazole Positron Emission Tomography in Humans After Ischemic Stroke
Authors: Markus R. , Reutens D.C. , Kazui S. , Read S. , Wright P. , Chambers B.R. , Sachinidis J.I. , Tochon-Danguy H.J. , Donnan G.A.
Published: October 2003

Background and Purpose—

We sought to characterize the spatial and temporal evolution of human cerebral infarction. Using a novel method of quantitatively mapping the distribution of hypoxic viable tissue identified by
18
F-fluoromisonidazole (
18
F-FMISO) PET relative to the final infarct, we determined its evolution and spatial topography in human stroke.

Methods—

Patients with acute middle cerebral artery territory stroke were imaged with
18
F-FMISO PET (n=19; <6 hours, 4; 6 to 16 hours, 4; 16 to 24 hours, 5; 24 to 48 hours, 6). The hypoxic volume (HV) comprised voxels with significant (
P
<0.05; >1 mL) uptake on statistical parametric mapping compared with 15 age-matched controls. Central, peripheral, and external zones of the corresponding infarct on the anatomically coregistered delayed CT were defined according to voxel distance from the infarct center and subdivided into 24 regions by coronal, sagittal, and axial planes. Maps (“penumbragrams”) displaying the percentage of HV in each region were generated for each time epoch.

Results—

Higher HV was observed in the central region of the infarct in patients studied within 6 hours of onset (analysis of covariance [ANCOVA];
P
<0.05) compared with those studied later, in whom the HV was mainly in the periphery or external to the infarct. HV was maximal in the superior, mesial, and posterior regions of the infarct (ANCOVA;
P
<0.05).

Conclusions—

These observations suggest that infarct expansion occurs at the expense of hypoxic tissue from the center to the periphery of the ischemic region in humans, similar to that seen in experimental animal models. These findings have important pathophysiological and therapeutic implications.
Strengthening Acute Stroke Trials Through Optimal Use of Disability End Points
Authors: Young Fiona B. , Lees Kennedy R. , Weir Christopher J.
Published: October 2003

Background and Purpose—

Suboptimal choices of primary end point for acute stroke trials may have contributed to inconclusive results. The Barthel Index (BI) and Rankin Scale (RS) have been widely used and analyzed in various ways. We sought to investigate the most powerful end point for use in acute stroke trials.

Methods—

Data from the Glycine Antagonist in Neuroprotection (GAIN) International Trial were used to simulate 24 000 clinical trials exploring various patterns and magnitudes of treatment effect and thus to estimate the statistical power for a range of end points based on the BI or RS.

Results—

RS end points were more powerful than BI end points. End points dichotomized toward the favorable extreme of either scale or adjusted according to baseline prognosis (“patient-specific” end point) were among the most powerful. Combining RS and BI in a “global” end point was also successful. Improvements in statistical power indicated that using a RS end point instead of BI ≥60 could reduce the sample size by up to 84% (95% CI, 80% to 87%), 73% (95% CI, 68% to 79%) for a patient-specific BI end point, or 81% (95% CI, 76% to 85%) for a global end point.

Conclusions—

The RS and global end points are preferable to BI end points; the position of the cut point is also important. Better choices of end point substantially strengthen trial power for a given trial size or allow reduced sample sizes without loss of statistical power.
Model Updating for the Identification of NIR Spectra from a Pharmaceutical Excipient
Authors: Candolfi Andrea , Massart D. L.
Published: October 2003

The effect of model updating on the identification of a pharmaceutical excipient based on its near-infrared (NIR) spectra has been investigated. A pragmatic updating approach, consisting of adding stepwise newly available samples to the training set and rebuilding the classification model, was applied. Its performance is compared for three pattern recognition methods: the wavelength distance method, the Mahalanobis distance method, and the SIMCA (soft independent modeling of class analogy) residual variance method. For the wavelength distance method, the updating approach is straightforward. In the case of the multivariate classification methods, which are based on a certain number of significant principal components (PCs), the selection of the number of PCs included in the model must be performed with care, as this number has a major impact on the classification results.
Simulation Studies on Modeling Process NMR Data by Using Chemometrics Approach
Authors: Lai Xiaonian , Sardashti Maziar , Lane Bobby J. , Gislason Jason J. , O'Donnell Daniel J.
Published: October 2003

A simulation study was conducted to evaluate the feasibility of using chemometrics methods to analyze process nuclear magnetic resonance (NMR) data. Using the computer-generated NMR data, training sets and validation sets were constructed to represent several real-world application scenarios. The experimental factors (the spectral noise, the reference measurement error, and the nonlinearity) that affect the performance of a partial least-square (PLS) model were systematically investigated.
CO Laser Absorption Coefficients for Gases of Biological Relevance: H2O, CO2, Ethanol, Acetaldehyde, and Ethylene
Authors: Persijn S. T. , Veltman R. H. , Oomens J. , Harren F. J. M. , Parker D. H.
Published: October 2003

The pressure-broadened spectra of water vapor, carbon dioxide, ethylene, ethanol, and acetaldehyde were recorded with the use of a liquid nitrogen-cooled CO laser-based photoacoustic spectrometer. The results obtained for CO2 and H2O gases were compared with those from the Hitran database. The absorption coefficients of ethylene, ethanol, and acetaldehyde on CO laser emission frequencies were determined as well. Finally, the measured spectra were used in a multicomponent analysis of trace gases released by pears ( Pyrus communis, cultivar Conference).
Hydride Generation Laser-Induced Fluorescence of Arsenic and Selenium in the Inductively Coupled Plasma and Electrothermal Atomizer
Authors: Pacquette H. L. , Elwood S. A. , Ezer M. , Swart D. J. , Simeonsson J. B.
Published: October 2003

The application of hydride generation (HG) sample introduction combined with laser-induced fluorescence (LIF) detection in the inductively coupled plasma (ICP) and electrothermal atomizer (ETA) is reported. Far-ultraviolet excitation of As at 193.696 nm and Se at 196.026 nm is accomplished by using a tunable dye laser system with frequency doubling and stimulated Raman scattering. HG-ICP-LIF and HG-ETA-LIF techniques have been developed and demonstrate good sensitivity and good linearity at the ng/mL to sub-ng/mL level for both elements. The relative standard deviation of replicate measurements is on the order of 3–10% at the 5 ng/mL level for the HG-ICP-LIF technique and 5–35% at the 0.6 ng/mL level for the HG-ETA-LIF technique. Detection limits of 1 ng/mL (5 ng absolute mass) for As and 0.06 ng/mL (0.3 ng) for Se are reported for the HG-ICP-LIF technique and 0.04 ng/mL (0.2 ng) for As and 0.16 ng/mL (0.8 ng) for Se are reported for the HG-ETA-LIF technique. Lower than expected sensitivity and precision are observed in the ETA, which may be due to inefficient trapping of the hydrides in the procedure. Selective HG procedures have been demonstrated for the speciation and recovery of selected oxidation states of As and Se. The analytical capabilities of the HG-LIF techniques are compared to those of other HG techniques, and recommendations are made for improved performance of future HG-LIF approaches.
Time-Resolved Laser-Induced Fluorescence of Uranium(VI) Hydroxo-Complexes at Different Temperatures
Authors: Eliet Véronique , Grenthe Ingmar , Bidoglio Giovanni
Published: October 2003

Fluorescence measurements were performed at different temperatures to increase the resolving capabilities of time-resolved laser-induced fluorescence for uranium speciation. This spectroscopic technique was used to determine the fluorescence lifetimes of the uranyl ion and the species UO2OH+, (UO2)2(OH)2+2, and (UO2)3 (OH)5+ in 0.5 M NaClO4 solutions at different pH and total uranium concentration and in the temperature range from 10 to 60 °C. The temperature dependence of the lifetimes was found to follow the Arrhenius law, and the activation energy of the process was determined for each species. The influence of temperature on the equilibrium constants of the uranium hydroxo-complexes was also considered.
Micro- and Sub-Nanosecond Lifetime Measurements Using a UV Light-Emitting Diode
Authors: Szmacinski Henryk , Chang Qing
Published: October 2003

The authors describe the use of an ultraviolet light-emitting diode (UV LED), Nichia NSHU590E, as a 373 nm excitation light source for fluorescence lifetime measurements. A frequency-domain technique has been chosen to demonstrate that the UV LED can be efficiently intensity modulated by driving the radio-frequency signal over a range of modulation frequencies from 10 kHz up to 330 MHz. Time-resolved measurements have been performed by using a fluorophore with a very long lifetime of 10.2 μs and fluorophore with a very short lifetime of 0.15 ns. Application of LEDs for lifetime-based chemical sensing is discussed.
Depth Profiling of Optical Absorption in Thin Films via the Mirage Effect and a New Inverse Scattering Theory. Part I: Principles and Methodology
Authors: Power J. F. , Fu S. W. , Schweitzer M. A.
Published: October 2003

Impulse mirage effect spectroscopy is developed in this work as a nondestructive method for depth profiling the optical properties of samples which are nearly thermally homogeneous with depth. Both a theory and an experimental methodology are presented. An inverse scattering theory of the experimental photothermal deflection signal is derived, based on a previous theory of the impulse mirage effect, which takes into account the effect of Fresnel diffraction on the probe beam. To reconstruct the depth profile of heat source density generated by light absorption in an unknown sample, we have applied our inverse theory to the experimental impulse response, using a regularized minimum square error reconstruction algorithm based on our previously published expectation minimum principle. Because this reconstruction problem is ill posed, it was necessary to identify and compensate for all experimental bias errors significantly affecting the fidelity of the depth profiles. A procedure for obtaining the overall best-fit model of the depth profile given the minimum prior experimental information is presented. These procedures have produced an agreement between the experimental and theoretically predicted mirage effect response to within typical root-mean-square error levels of 0.5% or less.
Infrared Spectroscopy of Human Cells and Tissue. Part VI: A Comparative Study of Histopathology and Infrared Microspectroscopy of Normal, Cirrhotic, and Cancerous Liver Tissue
Authors: Chiriboga Luis , Yee Herman , Diem Max
Published: October 2003

Infrared spectra of selected regions of normal, cirrhotic, and neoplastic liver tissue samples are reported. Spectra of these tissues may vary for a number of reasons that may or may not be related to the state of health or disease. With the use of histochemical and immunohistochemical methods, the spectral variations are interpreted in terms of the biochemical and pathological processes involved. This paper lays the groundwork for correlation of infrared spectroscopic and pathological/histochemical results for other tissues, to be reported in subsequent communications.
Anomalous Dispersion Effects in the IR-ATR Spectroscopy of Water
Authors: Hancer Mehmet , Sperline Roger P. , Miller Jan D.
Published: October 2003

The distortion of band shapes seen in infrared attenuated total reflection (IR-ATR) spectroscopy of strongly absorbing materials such as water, relative to transmission sampling, is shown here to be due to the anomalous dispersion (AD) of water. This distortion occurs in addition to the normal 1/ v dependence, and, contrary to previous reports, is shown to not be due to chemical changes of water at the interface between the optical element and bulk solution. IR-ATR spectra of water were modeled with approximation-free calculations. The modeled spectra are compared with experimental ATR spectra for different internal reflection elements, and the results are discussed in terms of the AD optical effect.
Method for Acquiring Low-Frequency Transmission Infrared Spectra of Adsorbed Compounds on Silica Gels
Authors: Cox J. K. , Tripp C. P.
Published: October 2003

A transmission infrared technique for detecting bands due to adsorbed species on silica gels in the region 4000 to 200 cm−1 is described. The region below 1300 cm−1 contains strong Si–O bulk modes that dominate the much weaker bands due to adsorbed species. Silica gels are strong infrared scatterers, and adsorbed molecules lead to changes in the spectral artifacts in the region containing the bulk modes. These artifacts dominate and mask out the much weaker bands due to adsorbed species. By embedding the silica gel in a pliable polymer film of similar refractive index, one minimizes the artifacts, enabling detection of bands attributed to adsorbed compounds.
Surface-Enhanced Raman Spectroscopic Investigation of Bacterial Lipolysis in a Skin Pore Phantom
Authors: Weldon Millicent K. , Morris Michael D.
Published: October 2003

Bacterial lipolysis of triglycerides is followed in a sebum pore phantom by microprobe surface-enhanced Raman scattering (SERS) spectroscopy. The phantom consists of a purpose-built syringe pump operating at physiological flow rates coupled to a 300 μm i.d. capillary. We employ silicon substrate SERS microprobes (50 μm × 700 μm) to monitor the lipolysis products. The silicon support allows some tip flexibility that makes these probes ideal for insertion into small structures. Propionibacterium acnes ( P. acnes) are immobilized on the inner surface of the capillary. These bacteria produce a lipase that hydrolyzes the triglycerides in a model sebum emulsion flowing through the capillary. The transformation is followed in vitro as changes in the SERS caused by lipolysis of triglyceride to free fatty acids. The acids adsorb as their carboxylates, and they can be readily identified by their characteristic spectra (carboxylate marker at ∼ 1390 cm−1).
Dual-Wavelength Resonance Raman Spectroscopy of Polydiacetylene Monolayers on Au Surfaces
Authors: Cai Mei , Mowery Mark D. , Pemberton Jeanne E. , Evans Christine E.
Published: October 2003

In this paper, resonance Raman spectroscopy with dual-wavelength laser excitation is applied to study the chromatic phase properties of self-assembled diacetylene monolayers on atomically flat Au surfaces. Laser excitation at 632.8 nm is utilized to exclusively monitor the longer conjugation length blue-phase polydiacetylene (PDA) backbone structure, while laser excitation at 514.5 nm is applied to probe the shorter conjugation length red phase. This experimental design allows in situ measurement of the photophysics and chemistry of the polymerization process within a single molecular layer. These studies demonstrate the presence of multiple chromatic species of PDAs within the same monolayer structure. Similar to observations for analogous thin film and multilayer assemblies, systematic conversion from the higher conjugation length blue form of the polymer to the shorter conjugation length red form is observed upon extended UV irradiation. Moreover, a very large Raman dispersion of 130 cm−1/eV is measured, demonstrating the highly conjugated nature of these monolayer polymers. Finally, backbone planarity and strain during the polymerization process are assessed by using the correlation of double- and triple-bond stretching frequencies.
Improved Fiber—Detector Coupling for MIR Spectroscopy Employing Shaped Silver Halide Fibers
Authors: Frank J. , Schindler R. , Lendl O. , Lendl B.
Published: October 2003

An improved fiber-detector coupling for mid-infrared (MIR) spectroscopy employing silver halide fibers (AgCl x Br1– x) and a mercury cadmium telluride (MCT) detector was developed. The key feature was the use of specially machined fiber pieces capable of focusing MIR radiation onto small detector elements. For this purpose new units for the machining and characterization of silver halide fibers were constructed. For fiber machining, a computer-controlled turning lathe was developed, which allowed highly precise fabrication of various fiber tips such as spherically, hyperboloidally, and paraboloidally shaped ones. The intensity distribution in space of MIR radiation emitted by the produced fibers was investigated with a dedicated MCT detector employing a flexible fiber-detector coupling. For this purpose the position of the fiber was kept constant while the light distribution in front of the fiber tip was scanned with the MCT element by moving the detector housing via stepper motors. Different fiber tip geometries were investigated for their influence on the spatial light distribution. With the use of shaped fiber tips, focusing of the IR beam was achieved, allowing the use of smaller detector elements, which in turn improves the signal-to-noise ratio in the case of MCT detection elements. Optimum conditions were found for fibers having a shape radius of 1 mm, being two times the fiber radius, whereas no significant differences between spherically and hyperboloidally as well as paraboloidally shaped fibers were observed. The developed fiber-detector coupling was furthermore combined with a fiber-optic flow-through cell for transmission measurement (optical path: 30 μm) and incorporated in a flow injection analysis system. With this experimental setup, reasonable MIR spectra of an aqueous sucrose solution could be recorded by injecting as little as 30 nL of sample containing 0.5 μg of sucrose.
D-β-Hydroxybutyrate Reaction Kinetics Studied in Nanoliter Volumes Using a Capillary Polarimeter
Authors: Swinney Kelly , Bornhop Darryl J.
Published: October 2003

A laser-based capillary polarimetric detector (CPD) has been configured to allow for the analysis of optically active molecules at physiological temperatures and within a 40 nL sample volume. In the CPD, interference fringes contained within a 360° fan of scattered light result from the interaction between a polarized laser beam and a 240 μm i.d. capillary tube. Here it is shown that these fringes change in a reproducible manner with solute optical activity, facilitating a 3σ detection limit of 1.7 × 10−3 M d-β-hydroxybutyrate corresponding to 68 × 10−12 mole (7 × 10−9 gram) of solute. Further, with the use of this improved and novel polarimeter, the noninvasive study of enzyme reaction kinetics for d-β-hydroxybutyrate (50 mg/dL) and hydroxybutyrate dehydrogenase (100 μL of 50 units/L) has been evaluated for the first time in the absence of NAD. The rate constant for this reaction was found to follow first-order kinetics and determined to be 2.2 × 10−2 s−1. The prospect of directly studying the influence of enzyme cofactors on reaction kinetics is at hand, and the observations presented suggest that the application of monitoring insulin therapy for patients experiencing ketoacidosis is a tractable problem for the CPD.
Comparison of 90° and Epi-Geometry for Two-Photon Excitation in Capillaries
Authors: Zugel S. A. , Lytle F. E.
Published: October 2003

Two geometries of excitation/emission optics are compared for two-photon excitation of time-resolved fluorescence in capillaries. The test fluorophore is the enzymatic tag β-naphthylamine (BNA). Two 0.25 NA (numerical aperture) microscope objectives are used in the 90° geometry: This configuration has a sensitivity of 1.9 × 1010 count M−1 min−1 and a detection limit of 2.5 nM [signal-to-noise (S/N) = 3]. The epi-geometry uses single objectives of 0.25, 0.50, or 1.25 NA. This second configuration has a sensitivity of 7.6 × 1010 count M−1 min−1 and a detection limit of 1.7 nM (S/N = 3) for the 1.25 NA objective. The similar performance of the two configurations is in stark contrast to the factor of 46 enhancement predicted by geometric optics for epi-excitation. The discrepancy is attributed to large increases in collected background counts, which make detection of the signal difficult.
Modeling Window Contributions to Four-Wave Mixing Spectra and Measurements of Third-Order Optical Susceptibilities
Authors: Murdoch Keith M. , Thompson David E. , Meyer Kent A. , Wright John C.
Published: October 2003

Line shapes of resonant features in four-wave mixing (FWM) spectra are modified by interferences between the electric fields produced by resonant and nonresonant nonlinear optical processes. In experiments on liquid samples, the windows of the optical cell can make a significant nonresonant contribution, and this must be treated correctly when modeling FWM spectra. A model is presented that fully treats the interference between sample and window contributions to FWM signals. A laminar flow cell, which eliminates windows from FWM experiments on liquids, was also demonstrated. Optical hyperpolarizabilities and susceptibilities were measured for FWM processes in liquid acetonitrile, liquid water, and borosilicate glass. A relatively small nonlinearity was found for nonresonant processes in water (γ = 8.6 × 10−38 cm6/erg), which would make it a useful solvent for vibrationally enhanced nonlinear spectroscopy. Experiments were performed to observe singly vibrationally enhanced (SIVE) processes associated with the fundamental stretch vibrations of water. No SIVE signal was detected, and an upper bound of γ < 3 × 10−37 cm6/erg was determined for its nonlinearity.
Characterization of Random Media by Low-Coherence Interferometry
Authors: Thurber S. R. , Brodsky A. M. , Burgess L. W.
Published: October 2003

We describe the use of low-coherence interferometry (LCI) for the structural characterization of nonuniform media with mesoscopic heterogeneities. The high sensitivity of LCI to the phase properties of scattered light makes it a suitable technique for the direct determination of size, concentration, and uniformity of heterogeneities in multi-phase systems. To demonstrate this, we examine using LCI to study a range of polystyrene microsphere suspensions with particle sizes ranging from 41 to 818 nm and concentrations from 0.25% to 10% by weight. The particle size and concentration information was extracted from the amplitude of the signal by using the theory of light scattering in nonuniform media. We have shown that the fluctuations in the unaveraged LCI signal may be utilized to extract additional information about system uniformity.
Confocal Raman Microscopy: Why the Depth Resolution and Spatial Accuracy Can Be Much Worse Than You Think
Authors: Everall Neil J.
Published: October 2003

This paper describes continuing studies on the effect of refraction on the depth resolution and spatial accuracy of confocal Raman microscopy. Previous work showed how the apparent position of interfaces, and their breadth, was grossly in error when “optical sectioning” was carried out with a high-power metallurgical objective (the usual configuration for commercial confocal Raman instruments). Simple equations were presented which model these effects given only the numerical aperture of the objective and sample refractive index. This paper extends these studies to the measurement of the position and thickness of buried structures and shows how the refraction theory provides a good basis for interpreting Raman intensity-depth profiles that have been acquired by optical sectioning of complex structures. To summarize the magnitude of the problem, it is typical for the apparent thickness and positional depth of a buried layer to be about half of the true values—hence, correcting for refraction is critical when interpreting intensity-depth profiles. In order to minimize the effects it is possible to use a specialized objective (e.g., an oil immersion objective) to reduce refraction at the sample surface. Data are presented which show that the apparent position and thickness of structures obtained with such an objective are much closer to the actual values, even when the sample index is not perfectly matched by the coupling fluid. The use of immersion objectives is highly recommended if depth profiling by optical sectioning is to be attempted.
Polarized Micro-Raman Study of Fluorapatite Single Crystals
Authors: Leroy G. , Leroy N. , Penel G. , Rey C. , Lafforgue P. , Bres E.
Published: October 2003

Despite the numerous Raman and infrared (IR) studies of the structure and the vibrational spectra of fluorapatite (FAp), the problem of the correlation of the observed and predicted bands still remains. An IR study of FAp powders was coupled with a micro-Raman polarized study of single-crystal FAp between 45 and 1100 cm−1. In order to observe all the polarization directions and to isolate all the symmetry species, the arrangement of Tsuda and Arends was modified. The results were compared with previously published data. Some discrepancies appeared between the band assignment predictions, the previously published results, and the experimental results. The presence of an E2 g band on the v1 mode was questioned, two Ag bands were observed for the v2 mode, and the Ag bands showed different behavior concerning the z(xx)z polarization direction. Such behavior was attributed to the orientation of molecular groups and their vibrations according to the polarization direction. Raman and IR spectroscopies provide dynamic information on the molecular structure, compared with diffraction data, which give information on the average atomic positions in the crystal lattice. This study applies the complementary techniques Raman and IR spectroscopy combined with diffraction data to obtain deeper knowledge of the FAp structure.
31P MAS-NMR Study of Some Alkali Rare-Earth Cyclo- and Polyphosphates
Authors: Moussa S. Ben , Iglesias J. E. , Trabelsi-Ayedi M. , Ferid M. , Sanz J.
Published: October 2003

Several alkali rare-earth polyphosphates have been analyzed by high-resolution 31P MAS-NMR (magic angle spinning nuclear magnetic resonance) spectroscopy. From their NMR spectra, the number and the multiplicity of crystallographic sites have been analyzed in the NH4LaP4O12 cyclophosphate and in MI2La(PO3)5 (M = NH4, K) and MILnIII(PO3)4 (M = Li, Na, Ag, K, Rb, Cs, Tl; Ln = La, Sm), long-chain polyphosphates. A linear dependence of NMR isotropic chemical shift values on the mean POP angles of the chain, calculated from data published on isostructural compounds, has been deduced. Chemical shift anisotropies of NMR components have been analyzed in terms of the structural characteristics of the environment of P atoms.
Fluorescence Fingerprint of Waters: Excitation-Emission Matrix Spectroscopy as a Tracking Tool
Authors: Yan Yuan , Li Hong , Myrick M. L.
Published: October 2003

In this report, an optical method for tracking sources of water entering rivers and oceans is applied to the Congaree River in Columbia, South Carolina. The Congaree River forms at the confluence of two rivers, the Saluda and the Broad. Excitation-emission matrix (EEM) spectra of water samples from the rivers were constructed by scanning emission spectra from 300 to 600 nm as a function of excitation wavelength from 200 to 290 nm. The two sources of water in the Congaree River were easily distinguishable on the basis of the EEM spectra of the water samples. In addition, the average composition of water in the Congaree River and hence the relative flow rates of inflowing Saluda and Broad Rivers could be determined. In this report, the characteristic fluorescence of the river water samples and the stability of the EEM spectra of the river samples over several months are presented.
Spatial Mapping of Electroluminescence Due to Impact Ionization in High Electron Mobility Transistors
Authors: Gaquiere C. , Boudart B. , Dhamelincourt P. A.
Published: October 2003

For the first time to our knowledge, the use of a Raman microspectrometer is proposed for recording electroluminescence spectra as well as generating complete electroluminescence maps of areas selected on the surface of a pseudomorphic high electron mobility transistor (PHEMT). More particularly, this microspectrometer was used to investigate the impact ionization effect in different regions of the PHEMT located between gate and drain.
Fast Atomic Mapping of Heterogeneous Surfaces Using Microline-Imaging Laser-Induced Breakdown Spectrometry
Authors: Mateo M. P. , Palanco S. , Vadillo J. M. , Laserna J. J.
Published: October 2003

A new approach for quick simultaneous and multielemental characterization of heterogeneous solid samples using laser-induced breakdown spectrometry (LIBS) is presented. The basic idea relies on focusing the incident laser beam with a cylindrical lens to produce a long and narrow microline plasma. The emitted light is then projected along the spectrograph slit, where each ablated location on the sample generates a signal at a defined height, and acquired with a charge-coupled device (CCD) detector. The method has been tested for compositional mapping of solar cells, enabling a 25-fold increase of analysis speed as compared to conventional LIBS configuration.
Pb/U Fractionation during Nd:YAG 213 nm and 266 nm Laser Ablation Sampling with Inductively Coupled Plasma Mass Spectrometry
Authors: Liu Haichen , Borisov Oleg V. , Mao Xianglei , Shuttleworth Stephen , Russo Richard E.
Published: October 2003

Elemental fractionation during laser ablation sampling was investigated by measuring Pb/U ratios in NIST 610 synthetic glass. Two Nd:YAG lasers with wavelengths of 213 and 266 nm were used to ablate the sample into an inductively coupled plasma mass spectrometer. Pb/U fractionation was observed to be similar for both laser wavelengths, and dependent on the irradiance. For representative Pb/U measurements, the necessary laser irradiance should be > 0.6 GW/cm2. However, if the laser beam is initially focused close to the sample surface, fractionation increases and is influenced by the formation of a crater during repetitive pulsing at a single sample location. As the ratio of crater depth to radius increases, plasma sampling and/or an effective irradiance decrease could cause additional fractionation. A good correlation was found between the fractionation of 14 elements in NIST 610 glass and the logarithms of their oxide melting temperatures.
γ-Ray Spectrometric and α-Counting Method Comparison for the Determination of Pb-210 in Estuarine Sediments
Authors: Tanner P. A. , Pan S. M. , Mao S. Y. , Yu K. N.
Published: October 2003

An intercomparison of methodology and of dating results, from α-counting and from the more recent γ-spectrometry method, has been made for marine sediment cores from several locations. The former method involves considerable chemical manipulation, whereas the latter is more straightforward and enables direct interpretation of the results. Similar precisions (∼ 12%) were found for both methods. With the constant flux model, the methods gave calculated sedimentation rates between 4.3 and 7.8 cm a−1 for replicate cores near a ferry pier in Hong Kong Harbor. The γ-spectrometry method is thus a reliable, more rapid method for routine monitoring and investigation of the harbor dynamics and history of pollution.
NIR Fiber-Optic Method with Multivariate Calibration Analysis for Determination of Inorganic Compounds in Aqueous Solutions
Authors: Han Ling , Lucas Donald , Littlejohn David , Kyauk Steven
Published: October 2003

Near-infrared spectra of aqueous solutions were collected by using evanescent-field fiber-optic sensors. The spectra of two- and four-electrolyte solutions were analyzed with a partial least-squares (PLS) algorithm to quantify the measurements. Our results indicate that the electrolytes can be identified and simultaneously determined by using the PLS calibration model. Electrolytes in opaque aqueous mixtures were also studied, and the results are compared with results from clear aqueous solutions.