45 research outputs found
Least-Squares Fitting of Multidimensional Spectra to Kubo Lineshape Models
No full textWe report a comprehensive study of the efficacy of least-squares fitting of multidimensional spectra to generalized Kubo lineshape models and introduce a novel least-squares fitting metric, termed the Scale Invariant Gradient Norm (SIGN), that enables a highly reliable and versatile algorithm. The precision of dephasing parameters is between 8× to 50× better for nonlinear model fitting compared to the CLS method, which effectively increases data acquisition efficiency by one to two orders of magnitude. Whereas the center-line-slope (CLS) method requires sequential fitting of both the nonlinear and linear spectra, our model fitting algorithm only requires nonlinear spectra, but accurately predicts the linear spectrum. We show an experimental example in which the CLS time constants differ by 60% for independent measurements of the same system, while the Kubo time constants differ by only 10% for model fitting. This suggests that model fitting is a far more robust method of measuring spectral diffusion than the CLS method, which is more susceptible to structured residual signals that are not removable by pure solvent subtraction. Statistical analysis of the CLS method reveals a fundamental oversight in accounting for the propagation of uncertainty by Kubo time constants in the process of fitting to the linear absorption spectrum. A standalone desktop app and source code for the least-squares fitting algorithm are freely available with example lineshape models and data. We have written the MATLAB source code in a generic framework where users may supply custom lineshape models. Using this application, a standard desktop fits a 12-parameter generalized Kubo model to a 106 data-point spectrum in a few minutes
SEMI-MELANISTIC WHITE-TAILED DEER IN NORTHERN WISCONSIN
No full textMelanistic color morphs of white-tailed deer (Odocoileus virginianus) are differentiated from other recognized color morphs by having uniform black hairs on the dorsal surface with subdued black hairs on the ventral surface, dark face and ears, a distinctive mid-dorsal stripe extending from the head to the apex of the tail, and a tail with black dorsally and white ventrally (Baccus and Posey 1999). Melanism results from the overproduction of the skin pigment melanin and is considered rare in white-tailed deer populations (Severinghaus and Cheatum 1956, Sauer 1984, Smith et al. 1984). Semi-melanistic deer have the same dark pelage colors as melanistic morphs, but patterns of white hairs are the same as those of normal color morphs (Baccus and Posey 1999). No literature records of melanism in white-tailed deer existed prior to 1929 (Seton 1929). Melanism has since been documented in north-central and southern Wisconsin (Anonymous 1948, Wozencraft 1979), South Carolina (Rue 1978), Michigan (Rue 1978), Texas (Smith et al. 1984, Baccus and Posey 1999), and Pennsylvania (D\u27Angelo and Baccus 2007). Semi-melanistic deer have been documented in New York (Townsend and Smith 1933), Idaho (Severinghaus and Cheatum 1956), and Texas (Bac(}us and Posey 1999). Herein, we report records for two semi-melanistic adult deer in northwestern Wisconsin
Least-Squares Fitting of Multidimensional Spectra to Kubo Line-Shape Models
No full textWe report a comprehensive
study of the efficacy of least-squares
fitting of multidimensional spectra to generalized Kubo line-shape
models and introduce a novel least-squares fitting metric, termed
the scale invariant gradient norm (SIGN), that enables a highly reliable
and versatile algorithm. The precision of dephasing parameters is
between 8× and 50× better for nonlinear model fitting compared
to that for the centerline-slope (CLS) method, which effectively increases
data acquisition efficiency by 1–2 orders of magnitude. Whereas
the CLS method requires sequential fitting of both the nonlinear and
linear spectra, our model fitting algorithm only requires nonlinear
spectra but accurately predicts the linear spectrum. We show an experimental
example in which the CLS time constants differ by 60% for independent
measurements of the same system, while the Kubo time constants differ
by only 10% for model fitting. This suggests that model fitting is
a far more robust method of measuring spectral diffusion than the
CLS method, which is more susceptible to structured residual signals
that are not removable by pure solvent subtraction. Statistical analysis
of the CLS method reveals a fundamental oversight in accounting for
the propagation of uncertainty by Kubo time constants in the process
of fitting to the linear absorption spectrum. A standalone desktop
app and source code for the least-squares fitting algorithm are freely
available, with example line-shape models and data. We have written
the MATLAB source code in a generic framework where users may supply
custom line-shape models. Using this application, a standard desktop
fits a 12-parameter generalized Kubo model to a 106 data-point
spectrum in a few minutes
Edge-pixel referencing suppresses correlated baseline noise in heterodyned spectroscopies
No full textTwo-dimensional infrared study of the C D and C O stretching vibrations in strongly hydrogen-bonded complexes
No full textSignatures of β-sheet secondary structures in linear and two-dimensional infrared spectroscopy
No full textUsing idealized models for parallel and antiparallel β sheets, we calculate the linear and two-dimensional infrared spectra of the amide I vibration as a function of size and secondary structure. The model assumes transition–dipole coupling between the amide I oscillators in the sheet and accounts for the anharmonic nature of these oscillators. Using analytical and numerical methods, we show that the nature of the one-quantum vibrational eigenstates, which govern the linear spectrum, is, to a large extent, determined by the symmetry of the system and the relative magnitude of interstrand interactions. We also find that the eigenstates, in particular their trends with system size, depend sensitively on the secondary structure of the sheet. While in practice these differences may be difficult to distinguish in congested linear spectra, we demonstrate that they give rise to promising markers for secondary structure in the two-dimensional spectra. In particular, distinct differences occur between the spectra of parallel and antiparallel bsheets and between β hairpins and extended β sheets.
An Annotated List Of The Snails Of Dallas County Texas
No full textAlthough great advances have been made in the study of many groups of Texas animals, the knowledge of the Mollusca is still very meager....[I]t is apparent that the study of Texas snails is only just begun and that there exists a need for careful and continued collecting in numerous counties. A molluscan survey of individual counties has been started by the senior author with the hope of ultimately bringing together a large mass of data to support a comprehensive and authentic treatment of the snails of Texas
