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Pyrene fluorescence after a high-energy electronic excitation exhibits a prominent band shoulder not present after excitation at low energies. The standard assignment of this shoulder as a non-Kasha emission from the second-excited state (S2) has been recently questioned. To elucidate this issue, we simulated the fluorescence of pyrene using two different theoretical approaches based on vertical convolution and nonadiabatic dynamics with nuclear ensembles. To conduct the necessary nonadiabatic dynamics simulations with high-lying electronic states and deal with fluorescence timescales of about 100 ns of this large molecule, we developed new computational protocols. The results from both approaches confirm that the band shoulder is, in fact, due to S2 emission. We show that the non-Kasha behavior is a dynamic-equilibrium effect not caused by a metastable S2 minimum. However, it requires considerable vibrational energy, which can only be achieved in collisionless regimes after transitions into highly excited states. This strict condition explains why the S2 emission was not observed in some experiments. [ABSTRACT FROM AUTHOR]

Myeloid-Derived Suppressor Cells (MDSCs), also known as 'Natural Suppressor Cells (NSCs)', 'Immature Myeloid Cells, (IMCs), or 'Myeloid Suppressor Cells' (MSCs), are renowned for suppressing the immune functioning of T lymphocytes. Depending on the structural similarity with neutrophils and monocytes, MDSCs can be classified as polymorphonuclear MDSCs (PMN-MDSCs) and monocytic MDSCs (M-MDSCs). On the other hand, T cells, generally subdivided into CD4+ and CD8+ groups based on the surface glycoprotein, are crucial for generating an adaptive immune response. During the event of an infection, MDSCs and T cells, along with other immune regulatory cells, interplay and generate a robust host immune response against the invading pathogens. In this review, we have highlighted the role of MDSCs and different subsets of CD4+ T cells, such as Th1, Th2, Th17, Th9, Th22, Treg, Tfh, and Tr1 with and various transcription factors associated with them, in different well known bacterial, viral, parasitic and fungal diseases. Changes in the MDSC population were found to be associated with either promotion or suppression of T cell subsets in different infections. The relative frequency and absolute numbers of MDSCs in the peripheral blood, therefore, may serve as an important marker useful in future immunotherapeutics. [ABSTRACT FROM AUTHOR]

Excited states relaxation in complex molecules often involves two types of nonradiative transitions, internal conversion (IC) and intersystem crossing (ISC). In the situations when the timescales of IC and ISC are comparable, an interplay between these two types of transitions can lead to complex nonadiabatic dynamics on multiple electronic states of different characters and spin multiplicities. We demonstrate that the generalized ab initio multiple spawning (GAIMS) method interfaced with the fast graphics processing unit-based TeraChem electronic structure code can be used to model such nonadiabatic dynamics involving both the IC and ISC transitions in molecules of moderate size. We carried out 1500 fs GAIMS simulations leading to the creation of up to 2500 trajectory basis functions to study the excited states relaxation in 2-cyclopentenone. After a vertical excitation from the ground state to the bright S2 state, the molecule quickly relaxes to the S1 state via conical intersection. The following relaxation proceeds along two competing pathways: one involves IC to the ground state, and the other is dominated by ISC to the low-lying triplet states. The time constants describing the population transfer between the six lowest singlet and triplet states predicted by the GAIMS dynamics are in good agreement with the characteristic times of IC and ISC obtained from the analysis of the time-resolved photoelectron spectrum. [ABSTRACT FROM AUTHOR]

This work aims to elucidate the dependence of the excited-state lifetime of adenine and adenosine on temperature. So far, it has been experimentally shown that while adenine's lifetime is unaffected by temperature, adenosine's lifetime strongly depends on it. However, the non-Arrhenius temperature dependence has posed a challenge in explaining this phenomenon. We used surface hopping to simulate the dynamics of adenine and adenosine in the gas phase at 0 and 400 K. The temperature effects were observed under the initial conditions via Wigner sampling with thermal corrections. Our results confirm that adenine's excited-state lifetime does not depend on temperature, while adenosine's lifetime does. Adenosine's dependency is due to intramolecular vibrational energy transfer from adenine to the ribose group. At 0 K, this transfer reduced the mean kinetic energy of adenine's moiety so much that internal conversion is inhibited, and the lifetime elongated by a factor of 2.3 compared to that at 400 K. The modeling also definitively ruled out the influence of viscosity, which was proposed as an alternative explanation previously. [ABSTRACT FROM AUTHOR]

Norm retrieval was introduced for Hilbert space frames for the first time by Bahmanpour et. al. in the year 2015. In order for a subspace as well as its orthogonal complement to do norm retrieval, it was proved by Bahmanpour et. al. that norm retrieval is a necessary requirement. Basically, norm retrieval refers to the process of reconstructing the signal's norm from the intensity measurements. We give a few characterizations for norm retrieval by vectors and subspaces under the action of bounded linear operators. [ABSTRACT FROM AUTHOR]