Effects of stand age, tree species, and climate on water table fluctuations and estimated evapotranspiration in managed peatland forests.

Lowland conifer forests dominated by black spruce (Picea mariana) and tamarack (Larix laricina) typically occur in peatlands in the boreal North American forest with near-surface water tables throughout the year. These forests are ecologically and economically important resources that may be impacted by climate change. However, information characterizing effects of forest disturbance, such as even-aged harvest on water table dynamics is needed to evaluate which forest tree species cover types are most hydrologically susceptible to even-aged harvest and changes in precipitation. We used a chronosequence approach to evaluate water table fluctuations and evapotranspiration across four stand age classes (<10, 15-30, 40-80, and >100-years old) and three distinct forest cover types (productive black spruce, stagnant black spruce, and tamarack) for a period of three years in Minnesota, USA. In general, there is limited evidence for elevated water tables in the younger age classes; the <10-year age class had no significant difference in mean weekly water table depth compared to the older age classes across all cover types. Estimated actual daily evapotranspiration (ET) generally agreed with the water table observations, with the exception of the tamarack cover type where ET was significantly lower in the <10-year age class. Productive black spruce sites that are 40-80-years old had higher evapotranspiration, and lower water table, possibly reflecting increased transpiration associated with the stem exclusion stage of stand development. Tamarack in the 40-80-year age class had higher water tables but no difference in ET compared to all other age classes, indicating that other external factors are driving higher water tables in that age class. To evaluate susceptibility to changing climate, we also assessed the sensitivity and response of water table dynamics to pronounced differences in growing season precipitation that occurred across study years. In general, tamarack forests are more sensitive to changes in precipitation compared to the two black spruce forest cover types. These findings can inform expected responses of site hydrology for a range of precipitation scenarios that may occur under future climate and be used by forest managers to evaluate hydrologic impacts of forest management activities across lowland conifer forest cover types.

Optogenetic manipulation of cardiac electrical dynamics using sub-threshold illumination: dissecting the role of cardiac alternans in terminating rapid rhythms.

Cardiac action potential (AP) shape and propagation are regulated by several key dynamic factors such as ion channel recovery and intracellular Ca2+ cycling. Experimental methods for manipulating AP electrical dynamics commonly use ion channel inhibitors that lack spatial and temporal specificity. In this work, we propose an approach based on optogenetics to manipulate cardiac electrical activity employing a light-modulated depolarizing current with intensities that are too low to elicit APs (sub-threshold illumination), but are sufficient to fine-tune AP electrical dynamics. We investigated the effects of sub-threshold illumination in isolated cardiomyocytes and whole hearts by using transgenic mice constitutively expressing a light-gated ion channel (channelrhodopsin-2, ChR2). We find that ChR2-mediated depolarizing current prolongs APs and reduces conduction velocity (CV) in a space-selective and reversible manner. Sub-threshold manipulation also affects the dynamics of cardiac electrical activity, increasing the magnitude of cardiac alternans. We used an optical system that uses real-time feedback control to generate re-entrant circuits with user-defined cycle lengths to explore the role of cardiac alternans in spontaneous termination of ventricular tachycardias (VTs). We demonstrate that VT stability significantly decreases during sub-threshold illumination primarily due to an increase in the amplitude of electrical oscillations, which implies that cardiac alternans may be beneficial in the context of self-termination of VT.

Anion intercalated graphite: a combined electrochemical and tribological investigation by in situ AFM.

The intercalation of graphite by electrochemical methods is an efficient strategy to produce massive graphene flakes. In fact, when graphite is biased inside an acidic solution, anions enter inside the stratified structure of the electrode and reduce the layer-to-layer interaction. Consequently, a gentle sonication is sufficient to disperse the graphene flakes inside the electrolyte. In view of an optimisation of the production protocol, a detailed analysis of the intercalation mechanism at the molecular length scale is mandatory. In the last 30 years, electrochemical (EC) scanning probe microscopies (e.g. EC-STM and in situ AFM) have been widely exploited in this research topic. In fact, these techniques have the possibility of combining the EC characterisation (e.g. cyclic-voltammetry, CV) with mechanical characterisation (e.g. adhesion and friction) and topography acquisition with high (molecular) lateral resolution. In this work, we investigate the tribological properties of the basal surface of graphite before and after the anion intercalation. By comparing the results acquired after the extraction of the graphite electrode from the EC cell with those collected inside the EC cell during the CV by an in situ AFM, we show how some features deriving from anisotropic friction can be exploited to unveil the very early stage of graphite exfoliation.

Quasi-thresholdless Photon Upconversion in Metal-Organic Framework Nanocrystals.

Photon upconversion based on sensitized triplet-triplet annihilation ( sTTA) is considered as a promising strategy for the development of light-managing materials aimed to enhance the performance of solar devices by recovering unused low-energy photons. Here, we demonstrate that, thanks to the fast diffusion of excitons, the creation of triplet pairs in metal-organic framework nanocrystals ( nMOFs) with size smaller than the exciton diffusion length implies a 100% TTA yield regardless of the illumination condition. This makes each nMOF a thresholdless, single-unit annihilator. We develop a kinetic model for describing the upconversion dynamics in a nanocrystals ensemble, which allows us to define the threshold excitation intensity  Ithbox required to reach the maximum conversion yield. For materials based on thresholdless annihilators, Ithbox is determined by the statistical distribution of the excitation energy among nanocrystals. The model is validated by fabricating a nanocomposite material based on nMOFs, which shows efficient upconversion under a few percent of solar irradiance, matching the requirements of real life solar technologies. The statistical analysis reproduces the experimental findings, and represents a general tool for predicting the optimal compromise between dimensions and concentration of nMOFs with a given crystalline structure that minimizes the irradiance at which the system starts to fully operate.

Real-time optical manipulation of cardiac conduction in intact hearts.

KEY POINTS: Although optogenetics has clearly demonstrated the feasibility of cardiac manipulation, current optical stimulation strategies lack the capability to react acutely to ongoing cardiac wave dynamics. Here, we developed an all-optical platform to monitor and control electrical activity in real-time. The methodology was applied to restore normal electrical activity after atrioventricular block and to manipulate the intraventricular propagation of the electrical wavefront. The closed-loop approach was also applied to simulate a re-entrant circuit across the ventricle. The development of this innovative optical methodology provides the first proof-of-concept that a real-time all-optical stimulation can control cardiac rhythm in normal and abnormal conditions. ABSTRACT: Optogenetics has provided new insights in cardiovascular research, leading to new methods for cardiac pacing, resynchronization therapy and cardioversion. Although these interventions have clearly demonstrated the feasibility of cardiac manipulation, current optical stimulation strategies do not take into account cardiac wave dynamics in real time. Here, we developed an all-optical platform complemented by integrated, newly developed software to monitor and control electrical activity in intact mouse hearts. The system combined a wide-field mesoscope with a digital projector for optogenetic activation. Cardiac functionality could be manipulated either in free-run mode with submillisecond temporal resolution or in a closed-loop fashion: a tailored hardware and software platform allowed real-time intervention capable of reacting within 2 ms. The methodology was applied to restore normal electrical activity after atrioventricular block, by triggering the ventricle in response to optically mapped atrial activity with appropriate timing. Real-time intraventricular manipulation of the propagating electrical wavefront was also demonstrated, opening the prospect for real-time resynchronization therapy and cardiac defibrillation. Furthermore, the closed-loop approach was applied to simulate a re-entrant circuit across the ventricle demonstrating the capability of our system to manipulate heart conduction with high versatility even in arrhythmogenic conditions. The development of this innovative optical methodology provides the first proof-of-concept that a real-time optically based stimulation can control cardiac rhythm in normal and abnormal conditions, promising a new approach for the investigation of the (patho)physiology of the heart.

Highly Fluorescent Metal-Organic-Framework Nanocomposites for Photonic Applications.

Metal-organic frameworks (MOFs) are porous hybrid materials built up from organic ligands coordinated to metal ions or clusters by means of self-assembly strategies. The peculiarity of these materials is the possibility, according to specific synthetic routes, to manipulate both the composition and ligands arrangement in order to control their optical and energy-transport properties. Therefore, optimized MOFs nanocrystals (nano-MOFs) can potentially represent the next generation of luminescent materials with features similar to those of their inorganic predecessors, that is, the colloidal semiconductor quantum dots. The luminescence of fluorescent nano-MOFs is generated through the radiative recombination of ligand molecular excitons. The uniqueness of these nanocrystals is the possibility to pack the ligand chromophores close enough to allow a fast exciton diffusion but sufficiently far from each other preventing the aggregation-induced effects of the organic crystals. In particular, the formation of strongly coupled dimers or excimers is avoided, thus preserving the optical features of the isolated molecule. However, nano-MOFs have a very small fluorescence quantum yield (QY). In order to overcome this limitation and achieve highly emitting systems, we analyzed the fluorescence process in blue emitting nano-MOFs and modeled the diffusion and quenching mechanism of photogenerated singlet excitons. Our results demonstrate that the excitons quenching in nano-MOFs is mainly due to the presence of surface-located, nonradiative recombination centers. In analogy with their inorganic counterparts, we found that the passivation of the nano-MOF surfaces is a straightforward method to enhance the emission efficiency. By embedding the nanocrystals in an inert polymeric host, we observed a +200% increment of the fluorescence QY, thus recovering the emission properties of the isolated ligand in solution.

Amino and carboxyl plasma functionalization of collagen films for tissue engineering applications.

Type I collagen films have been functionalized on their surfaces by plasma treatment with carboxyl and amino groups to improve their potential for grafting bioactive molecules. The physico-chemical properties of the plasma-treated films were evaluated and compared to the untreated materials by water contact angle, SEM and AFM. The presence of new functional groups on the film surfaces has been assessed by ATR-FTIR spectra after chemical derivatization. Moreover, the biocompatibility of the plasma-treated films was studied with MG-63 human osteoblast-like cells, evaluating cell proliferation, viability and morphology at 1, 3 and 7 days.

Nickel-assisted growth and selective doping of spinel-like gallium oxide nanocrystals in germano-silicate glasses for infrared broadband light emission.

The target of taking advantage of the near-infrared light-emission properties of nickel ions in crystals for the design of novel broadband optical amplifiers requires the identification of suitable nanostructured glasses able to embed Ni-doped nanocrystals and to preserve the workability of a glass. Here we show that Ni doping of Li(2)O-Na(2)O-Ga(2)O(3)-GeO(2)-SiO(2) glass (with composition 7.5:2.5:20:35:35 and melting temperature 1480 °C, sensibly lower than in Ge-free silicates) enables the selective embedding of nickel ions in thermally grown nanocrystals of spinel-like gallium oxide. The analysis of transmission electron microscopy and x-ray diffraction data as a function of Ni-content (from 0.01 to 1 mol%) indicates that Ni ions promote the nanophase crystallization without affecting nanoparticle size (~6 nm) and concentration (~4 × 10(18) cm(-3)). Importantly, as shown by optical absorption spectra, all nickel ions enter into the nanophase, with a number of ions per nanocrystal that depends on the nanocrystal concentration and ranges from 1 to 10(2). Photoluminescence data indicate that fast non-radiative decay processes become relevant only at mean ion-ion distances shorter than 1.4 nm, which enables the incorporation of a few Ni ions per nanoparticle without too large a worsening of the light-emission efficiency. Indeed, at 0.1 mol% nickel, the room temperature quantum yield is 9%, with an effective bandwidth of 320 nm.

Friction anisotropy of the surface of organic crystals and its impact on scanning force microscopy.

The transverse component of the friction forces acting on the tip of an atomic force microscope scanning on the surface of an organic crystal was monitored as a function of the scan direction. The relation between friction and the crystallographic system is disclosed, revealing that the symmetry of the friction phenomenon is dictated by the direction of the prominent corrugations of the crystal surface. It is also illustrated that molecular-resolution images can be collected through the monitoring of the motion of the tip in a transverse direction with respect to the scan direction.

From developmental biology to heart repair.

Advances in our understanding of cardiac development have fuelled research into cellular approaches to myocardial repair of the damaged heart. In this collection of reviews we present recent advances into the basic mechanisms of heart development and the resident and non-resident progenitor cell populations that are currently being investigated as potential mediators of cardiac repair. Together these reviews illustrate that despite our current knowledge about how the heart is constructed, caution and much more research in this exciting field is essential. The current momentum to evaluate the potential for cardiac repair will in turn accelerate research into fundamental aspects of myocardial biology.

Growth-related properties and postgrowth phenomena in organic molecular thin films.

The problem of monitoring the structural and morphological evolutions of thin films of organic molecular materials during their growth by organic molecular beam epitaxy and in the postgrowth stage is addressed here by a combination of in situ optical reflectance anisotropy measurements, ex situ optical and morphological investigations, and theoretical simulation of the material optical response. For alpha-quaterthiophene, a representative material in the class of organic molecular semiconductors, the results show that molecules crystallize in the first stage of growth in metastable structures, even when deposition is carried out at room temperature. In the postdeposition stage, the film structure evolves within a few days to the known equilibrium structure of the low temperature polymorph. When deposition is carried out at low substrate temperatures, an evolution of the film morphology is also demonstrated.

Tetracene thin films grown by organic molecular beam deposition under a static magnetic field.

The diamagnetic response of tetracene is exploited to increase the in-plane orientation of thin films grown by organic molecular beam deposition, while applying a magnetic field of 0.2 T parallel to the surface of the silica and potassium hydrogen phthalate substrates. The combined spectroscopic analysis of the films in the UV/visible region and morphological investigation of their surface performed by atomic force microscopy demonstrate a substantial increment of the film order when the magnetic field is applied along the c axis of potassium hydrogen phthalate, in agreement with the anisotropic magnetic susceptibility of tetracene.

Measured Davydov splitting in oligothiophene crystals.

The polarized absorption spectra of single crystals of oligothiophenes in a wide spectral range are reported. The experimental procedure is discussed, underlying several details which are relevant to obtain reliable spectra particularly for samples of increasing thickness. On the basis of these considerations, it has been possible to fully detect the transition to the upper Davydov exciton originating from the first molecular state. The position and shape of the main exciton peak in these materials are compared and discussed, taking into consideration the molecular arrangement and the longitudinal contribution which depends on the transition moment orientation. The Davydov splitting values as deduced from the experimental data at room temperature are also reported either for the first vibronic replica or for the electronic transition as a whole. The difference between the purely transverse and the measured Davydov splitting is discussed.

Lymph node metastases displaying lower Ki-67 immunostaining activity than the primary breast cancer.

UNLABELLED: The aim of the study was to verify by Ki-67 immunostaining if any difference exists in the cell proliferating fraction between primary breast tumors (PTs) and matching positive axillary lymph nodes (ALNs). PATIENTS AND METHODS: Immunohistochemistry with the monoclonal antibody against Ki-67 was performed in 160 node-positive breast carcinomas and in their respective lymph node metastases. RESULTS: An increase of Ki-67 immunoreactive cells in ALN compared with that of PTs was observed in 84% of cases (ALN: mean 17%, PTs: mean 8%; p < 0.001), whereas 16% of the cases showed Ki-67 value two to six times lower in the ALNs than in the corresponding PTs (ALN: mean 3.2%, PTs mean 12.5%; p < 0.005). The decrease of Ki-67 positive cells in the ALN was independent from the histotype and the histological grade of the tumor. CONCLUSION: A different cell proliferation fraction between PTs and matching positive ALNs was demonstrated and underlined that the existence of a group of patients with decreased number of Ki-67 immunoreactive cells in lymph node metastases compared with that of the primary tumors could be taken into account in the choice of therapeutic strategy.

Directional dispersion in absorbance spectra of oligothiophene crystals.

Due to the large oscillator strength of the first molecular transition in oligothiophenes, a strong directional dispersion of the b(u) exciton transition is expected originating from the macroscopic polarization field. Examining such dispersion unambiguously usually requires different faces to be accessible for the optical measurements. Alternatively, measurements carried out at different angles of incidence are met with intrinsic limits due to the peculiarities of wave propagation in such anisotropic systems. In order to demonstrate these limits along with the experimental difficulties involved, we examine refraction and absorption of light in these crystals and discuss the effects of directional dispersion on the absorbance spectra of quaterthiophene crystals.

Magnetically driven growth of anthracene thin films by organic molecular beam deposition.

The possible use of a static magnetic field during organic molecular beam deposition of thin molecular films for inducing some preferential growth is discussed and the magnetic properties of diamagnetic molecules and molecular crystals are recalled. Considering prototypical materials, namely anthracene molecules and potassium phthalate substrates, which interact and may give rise to polycrystalline films with specific orientations, we show that in the presence of a magnetic field the films display a macroscopic preferential orientation as a result of minimization of the magnetic energy contribution. A very good agreement between the results of optical spectroscopy, atomic force microscopy, and predictions made on the basis of the anisotropic magnetic susceptibility of anthracene is found.

Clinical relevance of thymidylate synthase expression in the signet ring cell histotype component of colorectal carcinoma.

Thymidylate Synthase (TS) is the key enzyme for DNA synthesis pathways and is inhibited by 5-fluorouracil (5FU). The aim of this work was to study TS expression and the proliferation rate in the different histological types of colorectal carcinoma (CRC). 50 patients with CRC were included in this study and evaluated immunohistochemically using the monoclonal antibodies, TS106 and Ki67. 20 tumours were of the intestinal type, 15 cases were signet ring cell carcinoma (SRCCs) and 15 cases were "mixed-type", with at least two different histological components. Intestinal and mucinous histotypes were positive for TS and Ki67, while "signet ring cell" samples were negative or showed only weak and focal positivity for both the TS and Ki67 antibodies. Our results show that signet ring cells (that are also often present in intestinal and mucinous carcinomas), are in the post-mitotic phase of the cell cycle and show a low proliferation index and TS expression. As TS is the key enzyme for DNA synthesis pathways and is inhibited by 5-fluorouracil (5FU), we can hypothesise that TS expression levels in the different histotypes of CRC could affect the potential responsiveness of these tumours to fluoropyrimidine chemotherapy, with a low efficacy being expected in signet ring cell areas.

Reflectivity and anisotropic optical functions of quaterthiophene single crystals.

Polarized reflectance spectra of quaterthiophene single crystals are reported with different angles and planes of incidence. The strong dependence of the spectral features on the experimental configuration is described by an orthorhombic model and the components of the complex diagonal dielectric tensor are given.