A New Approach to Polymorphism in Molecular Crystals: Substrate-Mediated Structures Revealed by Lattice Phonon Dynamics

The issue of polymorphism in molecular crystals is discussed, taking into account the substrate-mediated structures, that is, structures grown at the interface of different substrates. Bulk and thin films of a compound both share the potentiality to display different crystal forms. However, unlike bulk polymorphs, whose structures are determined by their different molecular packing, thin film structures depend very much on the molecular organization of the organic layers on the substrate, which may, or may not, lead to an ordered structure, depending on the nature of the interface and on the growth conditions. Based on large part in some of the authors' recent works, these thin film structures are classified as distorted bulk, substrate-selected and substrate-stabilized polymorphs, with some subtle differences which may yield a polymorph to belong not exclusively to a single one of these categories. Some experiments are then focused upon, involving charge transport at the interface, as well as how far the effect of the surface goes. Furthermore, the authors comment on how the surface-mediated structures evolve to the single crystal phase in the cases of pentacene and alpha-sexithiophene. Finally, the transition from a 3- to a 2D regime of growth is shortly discussed in terms of low-dimensional disorder

Terahertz Raman scattering as a probe for electron-phonon coupling, disorder and correlation length in molecular materials

Terahertz (or low-frequency) Raman spectroscopy has been shown to be a quite useful tool to infer important information on some key properties of molecular materials, like polymorphism, phase purity and phase transitions. Based on some of our recent studies, we present promising new directions and possible development of the technique for the characterization of electron-lattice phonon coupling, disorder and correlation length in systems of low-dimensionality. The relative strength of electron-lattice phonon coupling can be extracted from the intensities of the Raman bands in the pre-resonance Raman regime, as exemplified in the charge-transfer (CT) crystal N,N-dimethylphenazine-tetracyanoquinodimethane (M2P-TCNQ). Disorder is instead reflected in the Raman bandwidth, which we analyze with polarized light for systems of reduced dimensionality. The sample system studied for the one-dimensional case is the tetramethylbenzidine-tetrafluoroTCNQ CT crystal. As an example of a quasi two-dimensional (2D) system we address pentacene, the classical case of a monomolecular material widely studied for its application in organic electronics. Here the discussion is mostly related to the dispersion of the phonon branches, eventually leading to peculiar spectral profiles depending on the 2D or 3D regime of the films grown under different deposition conditions

Follicular dynamics in synchronized Italian Mediterranean buffalo cows

The aim of this study was to evaluate the length and the characteristics of the oestrous cycle in Italian Mediterranean buffalo cows, undergone synchronization of ovulation. The trial was performed on 32 buffaloes synchronized by the Ovsynch Program, which consists of an injection of GnRH on day 0, PGF2α on day 7 and GnRH on day 9. Starting on day 10 (Day 0 of the new cycle). Buffaloes undergone ultrasound examination of the ovaries on alternate days until the following heat. Follicular growth and corpus luteum formation and dimensions were recorded as well as the number of follicular waves. Statistical analysis was performed by ANOVA. Four animals (12.5%) did not show signs of oestrous and were excluded from the trial. The mean length of the oestrous cycle was 23.7±3.4 days. In particular, 1 animal (3.6%) showed an oestrous cycle characterized by 1 follicular wave with a length of 16 days, 17 subjects (60.7%) showed 2 follicular waves with a cycle length of 22.4±2.3 days and 10 buffaloes (35.7%) showed 3 follicular waves with a cycle of 26.8±2.0 days. These results confirm previous reports performed in buffalo species, although the cycle resulted longer in the 3-waves group

Chemical Doping of the Organic Semiconductor C8-BTBT-C8 Using an Aqueous Iodine Solution for Device Mobility Enhancement

The performance of organic field-effect transistors is still severely limited by factors such as contact resistance and charge trapping. Chemical doping is considered to be a promising key enabler for improving device performance, although there is a limited number of established doping protocols as well as a lack of understanding of the doping mechanisms. Here, a very simple doping methodology based on exposing an organic semiconductor thin film to an aqueous iodine solution is reported. The doped devices exhibit enhanced device mobility, which becomes channel-length independent, a decreased threshold voltage and a reduction in the density of interfacial traps. The device OFF current is not altered, which is in agreement with the spectroscopic data that points out that no charge transfer processes are occurring. Kelvin probe force microscopy characterization of the devices under operando conditions unambiguously proves that an important reduction of the contact resistance takes place after their exposition to the iodine solution, reaching almost ohmic contact

Effect of Benzoic Acids on Barite and Calcite Precipitation

The effect of various benzoic acids on the precipitation of barite (BaSO4) and calcite (CaCO3) was investigated. The acids varied in the number of carboxylate groups, from dibenzoic acids (phthalic, isophthalic, and terephthalic) through to the hexabenzoic acid (mellitic acid). It was found that the stereochemistry of the dibenzoic acids was important, as was the pH of the solution (trimesic acid was used as a test case and showed that greatest inhibition was achieved with all carboxylate groups deprotonated). Interestingly, for both the calcite and barite systems, mellitic acid was found to be both a potent inhibitor and a significant crystal growth modifier. In the case of barite, the presence of mellitic acid produced nanoparticles that agglomerated. The nanoparticles were found to be 20 nm in size from X-ray diffraction (XRD) line width analysis and 20-50 nm from transmission electron microscopy (TEM). Humic acid was also tested and found to form bundled fibers of barium sulfate

Prospective Validation of Diffusion-Weighted MRI as a Biomarker of Tumor Response and Oncologic Outcomes in Head and Neck Cancer: Results From an Observational Biomarker Pre-Qualification Study

PURPOSE: To determine DWI parameters associated with tumor response and oncologic outcomes in head and neck (HNC) patients treated with radiotherapy (RT). METHODS: HNC patients in a prospective study were included. Patients had MRIs pre-, mid-, and post-RT completion. We used T2-weighted sequences for tumor segmentation which were co-registered to respective DWIs for extraction of apparent diffusion coefficient (ADC) measurements. Treatment response was assessed at mid- and post-RT and was defined as: complete response (CR) vs. non-complete response (non-CR). The Mann-Whitney U test was used to compare ADC between CR and non-CR. Recursive partitioning analysis (RPA) was performed to identify ADC threshold associated with relapse. Cox proportional hazards models were done for clinical vs. clinical and imaging parameters and internal validation was done using bootstrapping technique. RESULTS: Eighty-one patients were included. Median follow-up was 31 months. For patients with post-RT CR, there was a significant increase in mean ADC at mid-RT compared to baseline ((1.8 ± 0.29) × 10-3 mm2/s vs. (1.37 ± 0.22) × 10-3 mm2/s, p \u3c 0.0001), while patients with non-CR had no significant increase (p \u3e 0.05). RPA identified GTV-P delta (Δ)ADCmean \u3c 7% at mid-RT as the most significant parameter associated with worse LC and RFS (p = 0.01). Uni- and multi-variable analysis showed that GTV-P ΔADCmean at mid-RT ≥ 7% was significantly associated with better LC and RFS. The addition of ΔADCmean significantly improved the c-indices of LC and RFS models compared with standard clinical variables (0.85 vs. 0.77 and 0.74 vs. 0.68 for LC and RFS, respectively, p \u3c 0.0001 for both). CONCLUSION: ΔADCmean at mid-RT is a strong predictor of oncologic outcomes in HNC. Patients with no significant increase of primary tumor ADC at mid-RT are at high risk of disease relapse

Intensity standardization methods in magnetic resonance imaging of head and neck cancer

BACKGROUND AND PURPOSE: Conventional magnetic resonance imaging (MRI) poses challenges in quantitative analysis because voxel intensity values lack physical meaning. While intensity standardization methods exist, their effects on head and neck MRI have not been investigated. We developed a workflow based on healthy tissue region of interest (ROI) analysis to determine intensity consistency within a patient cohort. Through this workflow, we systematically evaluated intensity standardization methods for MRI of head and neck cancer (HNC) patients.MATERIALS AND METHODS: Two HNC cohorts (30 patients total) were retrospectively analyzed. One cohort was imaged with heterogenous acquisition parameters (HET cohort), whereas the other was imaged with homogenous acquisition parameters (HOM cohort). The standard deviation of cohort-level normalized mean intensity (SD NMI c), a metric of intensity consistency, was calculated across ROIs to determine the effect of five intensity standardization methods on T2-weighted images. For each cohort, a Friedman test followed by a post-hoc Bonferroni-corrected Wilcoxon signed-rank test was conducted to compare SD NMI c among methods. RESULTS: Consistency (SD NMI c across ROIs) between unstandardized images was substantially more impaired in the HET cohort (0.29 ± 0.08) than in the HOM cohort (0.15 ± 0.03). Consequently, corrected p-values for intensity standardization methods with lower SD NMI c compared to unstandardized images were significant in the HET cohort (p &lt; 0.05) but not significant in the HOM cohort (p &gt; 0.05). In both cohorts, differences between methods were often minimal and nonsignificant. CONCLUSIONS: Our findings stress the importance of intensity standardization, either through the utilization of uniform acquisition parameters or specific intensity standardization methods, and the need for testing intensity consistency before performing quantitative analysis of HNC MRI.</p