Specific Heat and Transport “Anomalies” in Mixed Alkali Glasses

We show that changes in the relative mole fractions of Li2O and Na2O in alkali metaphosphate glasses lead to “anomalies” in the specific heat and structural relaxations. The heat capacity change between the liquid and glassy states, Δcp(Tg), at the calorimetric glass transition temperature, Tg, exhibits a minimum when the mole fractions of Li2O and Na2O are comparable. Moreover, systematic changes in the temperature dependence of the viscosity, η, i.e., changes in the “fragility” of the system, accompany these changes in mole fraction. This observed dependence of the “fragility” on the mixed alkali ion composition occurs in the absence of apparent changes in the covalent network connectivity which normally accounts for this behavior in glasses

LDRD final report on high power broadly tunable Mid-IR quantum cascade lasers for improved chemical species detection.

The goal of our project was to examine a novel quantum cascade laser design that should inherently increase the output power of the laser while simultaneously providing a broad tuning range. Such a laser source enables multiple chemical species identification with a single laser and/or very broad frequency coverage with a small number of different lasers, thus reducing the size and cost of laser based chemical detection systems. In our design concept, the discrete states in quantum cascade lasers are replaced by minibands made of multiple closely spaced electron levels. To facilitate the arduous task of designing miniband-to-miniband quantum cascade lasers, we developed a program that works in conjunction with our existing modeling software to completely automate the design process. Laser designs were grown, characterized, and iterated. The details of the automated design program and the measurement results are summarized in this report

LDRD final report on continuous wave intersubband terahertz sources.

There is a general lack of compact electromagnetic radiation sources between 1 and 10 terahertz (THz). This a challenging spectral region lying between optical devices at high frequencies and electronic devices at low frequencies. While technologically very underdeveloped the THz region has the promise to be of significant technological importance, yet demonstrating its relevance has proven difficult due to the immaturity of the area. While the last decade has seen much experimental work in ultra-short pulsed terahertz sources, many applications will require continuous wave (cw) sources, which are just beginning to demonstrate adequate performance for application use. In this project, we proposed examination of two potential THz sources based on intersubband semiconductor transitions, which were as yet unproven. In particular we wished to explore quantum cascade lasers based sources and electronic based harmonic generators. Shortly after the beginning of the project, we shifted our emphasis to the quantum cascade lasers due to two events; the publication of the first THz quantum cascade laser by another group thereby proving feasibility, and the temporary shut down of the UC Santa Barbara free-electron lasers which were to be used as the pump source for the harmonic generation. The development efforts focused on two separate cascade laser thrusts. The ultimate goal of the first thrust was for a quantum cascade laser to simultaneously emit two mid-infrared frequencies differing by a few THz and to use these to pump a non-linear optical material to generate THz radiation via parametric interactions in a specifically engineered intersubband transition. While the final goal was not realized by the end of the project, many of the completed steps leading to the goal will be described in the report. The second thrust was to develop direct THz QC lasers operating at terahertz frequencies. This is simpler than a mixing approach, and has now been demonstrated by a few groups with wavelengths spanning 65-150 microns. We developed and refined the MBE growth for THz for both internally and externally designed QC lasers. Processing related issues continued to plague many of our demonstration efforts and will also be addressed in this report

Infectious Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) Virus in Symptomatic Coronavirus Disease 2019 (COVID-19) Outpatients: Host, Disease, and Viral Correlates

Although severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infectious virus isolation in outpatients with coronavirus disease 2019 (COVID-19) has been associated with viral RNA levels and symptom duration, little is known about the host, disease, and viral determinants of infectious virus detection.COVID-19 adult outpatients were enrolled within 7 days of symptom onset. Clinical symptoms were recorded via patient diary. Nasopharyngeal swabs were collected to quantitate SARS-CoV-2 RNA by reverse transcriptase polymerase chain reaction and for infectious virus isolation in Vero E6-cells. SARS-CoV-2 antibodies were measured in serum using a validated ELISA assay.Among 204 participants with mild-to-moderate symptomatic COVID-19, the median nasopharyngeal viral RNA was 6.5 (interquartile range [IQR] 4.7–7.6 log10 copies/mL), and 26% had detectable SARS-CoV-2 antibodies (immunoglobulin (Ig)A, IgM, IgG, and/or total Ig) at baseline. Infectious virus was recovered in 7% of participants with SARS-CoV-2 antibodies compared to 58% of participants without antibodies (prevalence ratio [PR] = 0.12, 95% confidence interval [CI]: .04, .36; P = .00016). Infectious virus isolation was also associated with higher levels of viral RNA (mean RNA difference +2.6 log10, 95% CI: 2.2, 3.0; P < .0001) and fewer days since symptom onset (PR = 0.79, 95% CI: .71, .88 per day; P < .0001).The presence of SARS-CoV-2 antibodies is strongly associated with clearance of infectious virus. Seropositivity and viral RNA levels are likely more reliable markers of infectious virus clearance than subjective measure of COVID-19 symptom duration. Virus-targeted treatment and prevention strategies should be administered as early as possible and ideally before seroconversion.NCT04405570

VIBRATIONAL SPECTRA AND ANALYSIS OF SOME BORON-NITROGEN AND BORON-PHOSPHORUS COMPOUNDS

Author Institution: Department of Chemistry, University of South CarolinaThe infrared and Raman spectra of a number of boron-nitrogen and boron-phosphorus compounds have been recorded. Normal coordinate calculations have been carried out. Vibrational assignments will be presented. For some molecules, torsional frequencies have been observed and barriers to internal rotation calculated

Raman Spectroscopy Study of the Structure of Lithium and Sodium Ultraphosphate Glasses

Anhydrous binary phosphate glasses containing from 0 to 50 mol% Li 2O or Na 2O have been prepared and examined by Raman scattering spectroscopy. The unpolarized Raman spectrum of vitreous P 2O 5 has intense bands near 640 cm -1, attributed to the symmetric stretching mode of P-O-P bridging oxygens, (POP) sym, between Q 3 phosphate tetrahedra, and at 1390 cm -1 due to the symmetric stretch of the P=O terminal oxygens, (P=O) sym. With the addition of alkali oxide to P 2O 5, a new feature appears in the Raman spectra near 1160 cm -1 indicating the formation of Q 2 phosphate tetrahedra with two bridging and two non-bridging oxygens. The increase in relative amplitude of this new (PO 2) sym band with increasing modifier content is consistent with a simple depolymerization of the phosphate network. From 20 to 50 mol% alkali oxide, the position of the (P=O) sym Raman band decreases by ∼ 130 cm -1 whereas the frequency of the (POP) sym band increases by ∼ 60 cm -1. These frequency shifts are the result of π-bond delocalization on Q 3 species that effectively lengthens the P=O terminal oxygen bond and strengthens the P-O-P linkages with increasing alkali oxide content. The compositional dependence of the π-bond delocalization on Q 3 tetrahedra is described by considering the interconnections between neighboring Q 3 and Q 2 tetrahedra. The onset of π-bond delocalization on Q 3 species corresponds with the anomalous T g minimum at 20 mol% alkali oxide in alkali ultraphosphate glasses. The increase in T g between 20 and 50 mol% alkali oxide is attributed to the increased ionic interconnection of what becomes a chain-like phosphate network at higher alkali contents. Finally, the Raman spectra of several alkali ultraphosphate glasses show high frequency shoulders on the Raman bands attributed to the (PO 2) sym and (PO 2) asym vibrational modes. These shoulders represent the presence of strained structural units, possibly three-or four-membered rings. © 1998 Elsevier Science B.V

Mechanical Relaxation Anomalies in Mixed Alkali Oxides

Mechanical relaxation (MR) processes were investigated in single and mixed alkali (MA) metaphosphate glasses using a dynamic mechanical analyzer (DMA) over a range of frequencies, 0.1-50 Hz, and temperatures, 24-250°C. The mechanical loss modulus, M″, of each mixed, sodium and lithium, alkali glass exhibited two characteristic maxima, a large maximum just below Tg, and a well developed, yet considerably diminished in amplitude, maximum at a much lower temperature. The single alkali analogs, on the other hand, exhibited only a single maximum and this maximum appeared in the same location as the lower temperature peak observed in the MA glasses. The location of these maxima are identified with dynamic processes within the glass which occur with average frequencies, νμ(Na, Li), for the high T maximum in the mixed glasses, and νμ (Li) and νμ (Na) for the lithium and sodium glasses, respectively. These frequencies νμ(Na, Li), νμ (Li) and νμ (Na), varied exponentially with 1/T; νμ (Na, Li) had the largest activation energy. In addition νμ(Na, Li) ≪ νμ(Na) \u3c νμ(Li) for T \u3c Tg. Two other important observations were made, the high temperature maximum in M″ reached its largest amplitude when the mole fractions of Na2O and Li2O were comparable and νμ (Na, Li) exhibited a maximum in the same composition range. Our observations are discussed in light of a local site-memory relaxation model based on the notion that below Tg, cation hopping dynamics are intimately coupled with local glass network relaxations. © 1998 Elsevier Science B.V. All rights reserved

Optical Properties of Lanthanide-containing Halide-modified Zinc Tellurite Glasses

As part of an ongoing investigation to characterize the properties and structure of zinc halide-tellurium oxide glasses, we report preliminary measurements of the optical properties of several Nd- and Er-doped tellurites. Measurements include florescence lifetimes and estimates of the theoretical radiative lifetimes (as obtained by traditional Judd-Ofelt analysis of optical absorption spectra) as well as phonon sideband studies sensitive to vibrational characteristics near the rare earth ion. The response of these optical features to the substitution of alternative halides is examined