Three-Dimensional Effects on the Electronic Structure of Quasiperiodic Systems

We report on a theoreticl study of the electronic structure of quasiperiodic, quasi-one-dimensional systems where fully three dimensional interaction potentials are taken into account. In our approach, the actual physical potential acting upon the electrons is replaced by a set of nonlocal separable potentials, leading to an exactly solvable Schrodinger equation. By choosing an appropriate trial potential, we obtain a discrete set of algebraic equations that can be mapped onto a general tight-binding-like equation. We introduce a Fibonacci sequence either in the strength of the on-site potentials or in the nearest-neighbor distances, and we find numerically that these systems present a highly fragmented, self-similar electronic spectrum, which becomes singular continuous in the thermodynamical limit. In this way we extend the results obtained so far in one-dimensional models to the three-dimensional case. As an example of the application of the model we consider the chain polymer case.Comment: REVTeX 3.0, 19 pages, 6 figures (available upon request). To appear in Physica

Secondary Organic Aerosol Formation from the β-Pinene+NO3 System: Effect of Humidity and Peroxy Radical Fate

The formation of secondary organic aerosol (SOA) from the oxidation of β-pinene via nitrate radicals is investigated in the Georgia Tech Environmental Chamber (GTEC) facility. Aerosol yields are determined for experiments performed under both dry (relative humidity (RH) \u3c 2 %) and humid (RH = 50 % and RH = 70 %) conditions. To probe the effects of peroxy radical (RO2) fate on aerosol formation, RO2 + NO3 dominant and RO2 + HO2 dominant experiments are performed. Gas-phase organic nitrate species (with molecular weights of 215, 229, 231, and 245 amu, which likely correspond to molecular formulas of C10H17NO4, C10H15NO5, C10H17NO5, and C10H15NO6, respectively) are detected by chemical ionization mass spectrometry (CIMS) and their formation mechanisms are proposed. The NO+ (at m/z 30) and NO2+ (at m/z 46) ions contribute about 11 % to the combined organics and nitrate signals in the typical aerosol mass spectrum, with the NO+ : NO2+ ratio ranging from 4.8 to 10.2 in all experiments conducted. The SOA yields in the RO2 + NO3 dominant and RO2 + HO2 dominant experiments are comparable. For a wide range of organic mass loadings (5.1–216.1 μg m−3), the aerosol mass yield is calculated to be 27.0–104.1 %. Although humidity does not appear to affect SOA yields, there is evidence of particle-phase hydrolysis of organic nitrates, which are estimated to compose 45–74 % of the organic aerosol. The extent of organic nitrate hydrolysis is significantly lower than that observed in previous studies on photooxidation of volatile organic compounds in the presence of NOx. It is estimated that about 90 and 10 % of the organic nitrates formed from the β-pinene+NO3 reaction are primary organic nitrates and tertiary organic nitrates, respectively. While the primary organic nitrates do not appear to hydrolyze, the tertiary organic nitrates undergo hydrolysis with a lifetime of 3–4.5 h. Results from this laboratory chamber study provide the fundamental data to evaluate the contributions of monoterpene + NO3 reaction to ambient organic aerosol measured in the southeastern United States, including the Southern Oxidant and Aerosol Study (SOAS) and the Southeastern Center for Air Pollution and Epidemiology (SCAPE) study

Exciton Optical Absorption in Self-Similar Aperiodic Lattices

Exciton optical absorption in self-similar aperiodic one-dimensional systems is considered, focusing our attention on Thue-Morse and Fibonacci lattices as canonical examples. The absorption line shape is evaluated by solving the microscopic equations of motion of the Frenkel-exciton problem on the lattice, in which on-site energies take on two values, according to the Thue-Morse or Fibonacci sequences. Results are compared to those obtained in random lattices with the same stechiometry and size. We find that aperiodic order causes the occurrence of well-defined characteristic features in the absorption spectra which clearly differ from the case of random systems, indicating a most peculiar exciton dynamics. We successfully explain the obtained spectra in terms of the two-center problem. This allows us to establish the origin of all the absorption lines by considering the self-similar aperiodic lattices as composed of two-center blocks, within the same spirit of the renormalization group ideas.Comment: 16 pages in REVTeX 3.0. 2 figures on request to F. D-A ([email protected]

Energy spectra of quasiperiodic systems via information entropy

We study the relationship between the electronic spectrum structure and the configurational order of one-dimensional quasiperiodic systems. We take the Fibonacci case as an specific example, but the ideas outlined here may be useful to accurately describe the energy spectra of general quasiperiodic systems of technological interest. Our main result concerns the {\em minimization} of the information entropy as a characteristic feature associated to quasiperiodic arrangements. This feature is shown to be related to the ability of quasiperiodic systems to encode more information, in the Shannon sense, than periodic ones. In the conclusion we comment on interesting implications of these results on further developments on the issue of quasiperiodic order.Comment: REVTeX 3.0, 8 pages, 3 figures available on request from FD-A ([email protected]), Phys Rev E submitted, MA/UC3M/02/9

Fluorescence decay in aperiodic Frenkel lattices

We study motion and capture of excitons in self-similar linear systems in which interstitial traps are arranged according to an aperiodic sequence, focusing our attention on Fibonacci and Thue-Morse systems as canonical examples. The decay of the fluorescence intensity following a broadband pulse excitation is evaluated by solving the microscopic equations of motion of the Frenkel exciton problem. We find that the average decay is exponential and depends only on the concentration of traps and the trapping rate. In addition, we observe small-amplitude oscillations coming from the coupling between the low-lying mode and a few high-lying modes through the topology of the lattice. These oscillations are characteristic of each particular arrangement of traps and they are directly related to the Fourier transform of the underlying lattice. Our predictions can be then used to determine experimentally the ordering of traps.Comment: REVTeX 3.0 + 3PostScript Figures + epsf.sty (uuencoded). To appear in Physical Review

Music‐Based Interventions for People Living with Dementia, targeting Behavioral and Psychological Symptoms: A scoping review

IntroductionDementia care is a major public health issue worldwide. The management of behavioral and psychological symptoms (BPSD) is one of the hardest challenges in this context. Non-pharmacological strategies, like music-based interventions (Mbi), seem promising options, being considered low-risk, widely available and inclusive. This scoping review aimed at mapping all Mbi used in dementia care, targeting BPSD, and debriefing its components, structure and rationale. Music therapy and other therapeutic music activities were included.MethodsThe Arksey and O'Malley framework, Cochrane recommendations and PRISMA checklist were followed. Embase, PubMed, PsycINFO, ASSIA and Humanities Index were searched from first records until the 31st of March 2020. Snowballing process and screening of relevant journals were also undertaken. A panel of experts critically guided the evidence synthesis.ResultsOverall, 103 studies (34 RCT; 12 NRT; 40 Before/After studies and 17 Case Studies) met inclusion criteria. Basic elements of the Mbi, the rationale supporting its development and hypothesis tested were mostly underreported, thus hampering cross-study comparisons and generalizations. Despite this, available evidence indicates that: it is feasible to deliver Mbi to PwD at very different stages and in different settings - from community to the acute setting - even for non-music therapists; positive or neutral effects in BPSD are often reported but not without exception; individualization seems a critical factor mediating Mbi effects.ConclusionsDetailed intervention and research reporting are essential to interpretation, replication and translation into practice. Ten years after the publication of specific reporting guidelines, this goal is not yet fully achieved in music in dementia care

Cellular and acellular assays for measuring oxidative stress induced by ambient and laboratory-generated aerosol

Exposure to atmospheric particulate matter (PM) is a leading global health risk with various proposed mechanisms of action, including the induction of oxidative stress through PM-initiated production/release of reactive oxygen and nitrogen species (ROS/RNS). This dissertation explores cellular and acellular measurements of PM-induced oxidative stress through systematic laboratory chamber experiments and ambient field studies. A cell-based assay involving murine alveolar macrophages was developed to measure intracellular ROS/RNS produced as a result of aerosol exposure. The area under the dose-response curve was identified as a robust metric to represent ROS/RNS for comparison with different endpoints. A large ambient study with samples collected from urban and rural sites around the greater Atlanta area (n = 104) was conducted using the optimized assay and significant correlations between ROS/RNS and organic constituents were observed for summer samples, highlighting the potential contribution of organic aerosol, particularly summertime photochemically-driven secondary organic aerosol (SOA). To explore these findings, SOA was generated in a series of laboratory experiments from various biogenic (isoprene, α-pinene, β-caryophyllene) and anthropogenic (pentadecane, m-xylene, naphthalene) precursors under different formation conditions (dry vs. humid, NOx, ammonium sulfate vs. iron sulfate seed particles) to probe their effects on PM toxicity. For chemical oxidative potential as measured by dithiothreitol consumption (OP), precursor identity influenced toxicity significantly, with isoprene and naphthalene SOA having the lowest and highest OP, respectively. Both precursor identity and formation conditions influenced ROS/RNS and cytokine (tumor necrosis factor-α and interleukin-6) production. Several response patterns were identified for SOA precursors whose photooxidation products share similar carbon chain length and functionalities. A significant correlation between ROS/RNS levels and aerosol carbon oxidation state was also observed, which may have significant implications as atmospheric aerosol have an atmospheric lifetime of a week, over which oxidation state increases due to photochemical aging, potentially resulting in more toxic aerosol.Ph.D