One-Pot Synthesis of Bioinspired Peptide-Decorated Apatite Nanoparticles for Nanomedicine.

Hybrid organic-inorganic bio-inspired apatite nanoparticles (NPs) are attractive for biomedical applications and especially in nanomedicine. Unfortunately, their applications in nanomedicine are limited by their broad particle size distributions and uncontrolled drug loading due to their multistep synthesis process.  Besides, very few attempts at exposing bioactive peptides on apatite NPs are made. In this work, an original one-pot synthesis of well-defined bioactive hybrid NPs composed of a mineral core of bioinspired apatite surrounded by an organic corona of bioactive peptides is reported. Dual stabilizing-bioactive agents, phosphonated polyethylene glycol-peptide conjugates, are prepared and directly used during apatite precipitation i) to form the organic corona during apatite precipitation, driving the size and shape of resulting hybrid NPs with colloidal stabilization and ii) to expose peptide moieties (RGD or YIGSR sequences) at the NPs periphery in view of conferring additional surface properties to enhance their interaction with cells. Here, the success of this approach is demonstrated, the functionalized NPs are fully characterized by Fourier-transform infrared, Raman, X-ray diffraction, solid and liquid state NMR, transmission electron microscopy, and dynamic light scattering, and their interaction with fibroblast cells is followed, unveiling a synergistic proliferative effect.

Silica Supported Organometallic IrI Complexes Enable Efficient Catalytic Methane Borylation.

Catalytic C-H borylation is an attractive method for the conversion of the most abundant hydrocarbon, methane (CH4), to a mild nucleophilic building block. However, existing CH4 borylation catalysts often suffer from low turnover numbers and conversions, which is hypothesized to result from inactive metal hydride agglomerates. Herein we report that the heterogenization of a bisphosphine molecular precatalyst, [(dmpe)Ir(cod)CH3], onto amorphous silica dramatically enhances its performance, yielding a catalyst that is 12-times more efficient than the current standard for CH4 borylation. The catalyst affords over 2000 turnovers at 150 °C in 16 h with a selectivity of 91.5% for mono- vs diborylation. Higher catalyst loadings improve yield and selectivity for the monoborylated product (H3CBpin) with 82.8% yield and >99% selectivity being achieved with 1255 turnovers. X-ray absorption and dynamic nuclear polarization-enhanced solid-state NMR spectroscopic studies identify the supported precatalyst as an IrI species, and indicate that upon completion of catalysis, multinuclear Ir polyhydrides are not formed. This is consistent with the hypothesis that immobilization of the organometallic Ir species on a surface prevents bimolecular decomposition pathways. Immobilization of the homogeneous IrI fragment onto amorphous silica represents a unique and simple strategy to improve the TON and longevity of a CH4 borylation catalyst.

Exploring the emergence of a tipping point for conservation with increased recognition of social considerations.

Despite a common understanding of the harmful impacts of Western conservation models that separate people from nature, widespread progress toward incorporating socioeconomic, political, cultural, and spiritual considerations in conservation practice is lacking. For some, the concept of nature-based solutions (NbS) is seen as an interdisciplinary and holistic pathway to better integrate human well-being in conservation. We examined how conservation practitioners in the United States view NbS and how social considerations are or are not incorporated in conservation adaptation projects. We interviewed 28 individuals working on 15 different such projects associated with the Wildlife Conservation Society's Climate Adaptation Fund. We completed 2 rounds of iterative coding in NVivo 12.6.1 to identify in the full text of all interview responses an a priori set of themes related to our research questions and emergent themes. Many respondents saw this moment as a tipping point for the field (one in which the perceived values of social considerations are increasing in conservation practice) (76%) and that social justice concerns and the need to overcome racist and colonial roots of Western conservation have risen to the forefront. Respondents also tentatively agreed that NbS in conservation could support social and ecological outcomes for conservation, but that it was far from guaranteed. Despite individual intention and awareness among practitioners to incorporate social considerations in conservation practice, structural barriers, including limited funding and inflexible grant structures, continue to constrain systemic change. Ultimately, systemic changes that address power and justice in policy and practice are required to leverage this moment to more fully address social considerations in conservation.

Exploración del surgimiento de un punto de inflexión para la conservación con el incremento del reconocimiento de las consideraciones sociales Resumen A pesar de que se conoce el impacto dañino de los modelos occidentales de conservación que separan a las personas de la naturaleza, aun faltan avances para la incorporación de las consideraciones socioeconómicas, políticas, culturales y espirituales dentro de la práctica de la conservación. Hay quienes consideran el concepto de soluciones basadas en la naturaleza (SbN) como una vía interdisciplinaria y holística para integrar de mejor manera el bienestar humano en la conservación. Analizamos cómo los conservacionistas de los EE. UU. perciben a las SbN y cómo se incorporan o no las consideraciones sociales en los proyectos de conservación y adaptación. Entrevistamos a 28 individuos que trabajan en 15 de estos proyectos asociados con el Fondo de Adaptación al Clima de la Wildlife Conservation Society. Completamos dos rondas de codificación iterativa en NVivo 12.6.1 para identificar a priori un conjunto de temas relacionado con nuestras preguntas y temas nacientes dentro del texto completo de las respuestas a la entrevista. Muchos de los respondientes (76%) consideraron este momento como un punto de inflexión para el campo de investigación (uno en el que están incrementando los valores percibidos de las consideraciones sociales en la práctica de la conservación) y que las cuestiones de justicia social y la necesidad de sobreponerse a las raíces racistas y colonialistas de la conservación occidental han dado un paso al frente. En principio, los respondientes también acordaron que las SbN en la conservación podrían respaldar los resultados sociales y ecológicos para la conservación, pero que no era algo cercano a ser una garantía. A pesar de la intención y conciencia individual de los conservacionistas para incorporar a las consideraciones sociales dentro de la práctica de la conservación, las barreras estructurales, incluyendo el financiamiento limitado de las estructuras poco flexibles de los subsidios, todavía restringen el cambio sistémico. Finalmente, se necesitan cambios sistémicos que aborden el poder y la justicia en las políticas y las prácticas para potenciar este momento para tratar plenamente las consideraciones sociales en la conservación.

Fast autofocusing using tiny transformer networks for digital holographic microscopy.

The numerical wavefront backpropagation principle of digital holography confers unique extended focus capabilities, without mechanical displacements along z-axis. However, the determination of the correct focusing distance is a non-trivial and time consuming issue. A deep learning (DL) solution is proposed to cast the autofocusing as a regression problem and tested over both experimental and simulated holograms. Single wavelength digital holograms were recorded by a Digital Holographic Microscope (DHM) with a 10x microscope objective from a patterned target moving in 3D over an axial range of 92 µm. Tiny DL models are proposed and compared such as a tiny Vision Transformer (TViT), tiny VGG16 (TVGG) and a tiny Swin-Transfomer (TSwinT). The proposed tiny networks are compared with their original versions (ViT/B16, VGG16 and Swin-Transformer Tiny) and the main neural networks used in digital holography such as LeNet and AlexNet. The experiments show that the predicted focusing distance ZRPred is accurately inferred with an accuracy of 1.2 µm in average in comparison with the DHM depth of field of 15 µm. Numerical simulations show that all tiny models give the ZRPred with an error below 0.3 µm. Such a prospect would significantly improve the current capabilities of computer vision position sensing in applications such as 3D microscopy for life sciences or micro-robotics. Moreover, all models reach an inference time on CPU, inferior to 25 ms per inference. In terms of occlusions, TViT based on its Transformer architecture is the most robust.

A Heterogeneous Palladium Catalyst for the Polymerization of Olefins Prepared by Halide Abstraction Using Surface R3 Si+ Species.

The silylium-like surface species [i Pr3 Si][(RF O)3 Al-OSi≡)] activates (N^N)Pd(CH3 )Cl (N^N=Ar-N=CMeMeC=N-Ar, Ar=2,6-bis(diphenylmethyl)-4-methylbenzene) by chloride ion abstraction to form [(N^N)Pd-CH3 ][(RF O)3 Al-OSi≡)] (1). A combination of FTIR, solid-state NMR spectroscopy, and reactions with CO or vinyl chloride establish that 1 shows similar reactivity patterns as (N^N)Pd(CH3 )Cl activated with Na[B(ArF )4 ]. Multinuclear 13 C{27 Al} RESPDOR and 1 H{19 F} S-REDOR experiments are consistent with a weakly coordinated ion-pair between (N^N)Pd-CH3 + and [(RF O)3 Al-OSi≡)]. 1 catalyzes the polymerization of ethylene with similar activities as [(N^N)Pd-CH3 ]+ in solution and incorporates up to 0.4 % methyl acrylate in copolymerization reactions. 1 produces polymers with significantly higher molecular weight than the solution catalyst, and generates the highest molecular weight polymers currently reported in copolymerization reactions of ethylene and methylacrylate.

Social comfort zones for transformative conservation decisions in a changing climate.

Novel management interventions intended to mitigate the impacts of climate change on biodiversity are increasingly being considered by scientists and practitioners. However, resistance to more transformative interventions remains common across both specialist and lay communities and is generally assumed to be strongly entrenched. We used a decision-pathways survey of the public in Canada and the United States (n = 1490) to test two propositions relating to climate-motivated interventions for conservation: most public groups are uncomfortable with interventionist options for conserving biodiversity and given the strong values basis for preferences regarding biodiversity and natural systems more broadly, people are unlikely to change their minds. Our pathways design tested and retested levels of comfort with interventions for forest ecosystems at three different points in the survey. Comfort was reexamined given different nudges (including new information from trusted experts) and in reference to a particular species (bristlecone pine [Pinus longaeva]). In contrast with expectations of public unease, baseline levels of public comfort with climate interventions in forests was moderately high (46% comfortable) and increased further when respondents were given new information and the opportunity to change their choice after consideration of a particular species. People who were initially comfortable with interventions tended to remain so (79%), whereas 42% of those who were initially uncomfortable and 40% of those who were uncertain shifted to comfortable by the end of the survey. In short and across questions, comfort levels with interventions were high, and where discomfort or uncertainty existed, such positions did not appear to be strongly held. We argue that a new decision logic, one based on anthropogenic responsibility, is beginning to replace a default reluctance to intervene with nature.

Zonas de Comodidad Social ante las Decisiones de Conservación Transformadoras en un Clima Cambiante Resumen Los científicos y los practicantes de la conservación cada vez consideran más a las intervenciones novedosas de manejo con la intención de mitigar los impactos del cambio climático sobre la biodiversidad. Sin embargo, la resistencia a las intervenciones más transformadoras es común en especialistas y no profesionales y generalmente se asume que está fuertemente arraigada. Usamos una encuesta sobre toma de decisiones del público en Canadá y en los Estados Unidos (n = 1490) para evaluar dos propuestas relacionadas a intervenciones de conservación motivadas por el clima: la mayoría de los grupos de público están incómodos con las opciones intervencionistas para conservar la biodiversidad y dada la sólida base de valores para las preferencias con respecto a la biodiversidad y a los sistemas naturales en general, es poco probable que las personas cambien de opinión. Nuestro diseño de encuesta analizó y reanalizó los niveles de comodidad con respecto a las intervenciones para los ecosistemas boscosos en tres puntos distintos dentro del estudio. La comodidad fue reexaminada con diferentes impulsos (incluyendo información nueva proveniente de expertos confiables) y en referencia a una especie particular (Pinus longaeva). Contrario a las expectativas de malestar del público, los niveles de línea base de la comodidad del público frente a las intervenciones climáticas en los bosques fueron moderadamente altos (46% de comodidad) e incrementaron cuando a los respondientes se les proporcionó información nueva y la oportunidad de cambiar su elección después de considerar a una especie particular. Las personas que al inicio estaban cómodas con las intervenciones tendieron a permanecer así (79%), mientras que el 42% de aquellos que estuvieron incómodos inicialmente y el 40% de aquellos que estuvieron inseguros cambiaron a estar cómodos para el final del estudio. En resumen, los niveles de comodidad frente a las intervenciones fueron elevados, y cuando existieron malestar o incertidumbre, dichas posiciones no parecieron mantenerse con fuerza. Argumentamos que una lógica de decisión basada en la responsabilidad antropogénica está comenzando a reemplazar una renuencia predeterminada a intervenir en la naturaleza.

Solid-State Phase Transformation and Self-Assembly of Amorphous Nanoparticles into Higher-Order Mineral Structures.

Materials science has been informed by nonclassical pathways to crystallization, based on biological processes, about the fabrication of damage-tolerant composite materials. Various biomineralizing taxa, such as stony corals, deposit metastable, magnesium-rich, amorphous calcium carbonate nanoparticles that further assemble and transform into higher-order mineral structures. Here, we examine a similar process in abiogenic conditions using synthetic, amorphous calcium magnesium carbonate nanoparticles. Applying a combination of high-resolution imaging and in situ solid-state nuclear magnetic resonance spectroscopy, we reveal the underlying mechanism of the solid-state phase transformation of these amorphous nanoparticles into crystals under aqueous conditions. These amorphous nanoparticles are covered by a hydration shell of bound water molecules. Fast chemical exchanges occur: the hydrogens present within the nanoparticles exchange with the hydrogens from the surface-bound H2O molecules which, in turn, exchange with the hydrogens of the free H2O molecule of the surrounding aqueous medium. This cascade of chemical exchanges is associated with an enhanced mobility of the ions/molecules that compose the nanoparticles which, in turn, allow for their rearrangement into crystalline domains via solid-state transformation. Concurrently, the starting amorphous nanoparticles aggregate and form ordered mineral structures through crystal growth by particle attachment. Sphere-like aggregates and spindle-shaped structures were, respectively, formed from relatively high or low weights per volume of the same starting amorphous nanoparticles. These results offer promising prospects for exerting control over such a nonclassical pathway to crystallization to design mineral structures that could not be achieved through classical ion-by-ion growth.

Design of an optically-locked interferometer for attosecond pump-probe setups.

We present the design and performance of an active stabilization system for attosecond pump-probe setups based on a Mach-Zehnder interferometer configuration. The system employs a CW laser propagating coaxially with the pump and probe beams in the interferometer. The stabilization is achieved with a standalone feedback controller that adjusts the length of one of its arms to maintain a constant relative phase between the CW beams. With this system, the time delay between the pump and probe beams is stabilized within 10 as rms over several hours. The system is easy to operate and only requires a few minutes to set up before any pump/probe measurements.

Public trust and knowledge in the context of emerging climate-adaptive forestry policies.

Effective governance of public forests depends, in part, on public support for changes in forest management, particularly those responding to changes in socio-ecological conditions driven by climate change. Trust in managing authorities and knowledge about forest management have proven influential in shaping public support for policy across different forest managemen contexts. However, little is known about the relationship between public trust and knowledge as it relates to policy support for emerging management strategies for climate adaptation in forests. We use the example of genomics-based assisted migration (within and outside of natural range) in British Columbia's (BC) forests to examine the relative roles of and interactions between trust in different forestry actors and knowledge of forestry in shaping public support for this new and potentially controversial management alternative. Our results, based on an online survey (n = 1953 BC residents), reveal low public trust in governments and the forest industry combined with low levels of public knowledge about forest management. We find that individuals who are more trusting of decision-makers and other important forestry actors hold higher levels of support for assisted migration. Higher levels of forestry knowledge are linked with support for assisted migration within native range, whereas no knowledge effect is observed for assisted migration outside of native range. We discuss the implications of these observations and provide recommendations to more fully engage with the challenges of low levels of trust and knowledge in this context.

Response to Critique of "The Insignificance of Thresholds in Environmental Impact Assessment: An Illustrative Case Study in Canada".

Our paper, "The Insignificance of Thresholds in Environmental Impact Assessment: An Illustrative Case Study in Canada" received a critique that challenged us on a number of grounds. Namely, that we defame EIA practitioners, that we advocate EIAs to become a scientific enterprise, that we do not recognize the complexity inherent in EIA, and that EIA undergo an independent assessment by regulators. We respond to all of these points, and argue that conflict of interest is an institutional issue (not one of corrupt practitioners), and that we critique the science that forms the basis of evidence in EIA. Further, we show that the complexity and uncertainty in the critique cannot explain the findings from our paper that all cases of impact threshold exceedance were determined to be not significant in EIA. Finally, we compare the significance determinations in proponent reports to final regulator decisions and determine that they are overwhelmingly identical (93-95%). Regulators are financially independent of proponents, but their decisions on significant are heavily dependent on the information and analysis provided by the proponent reports. As regulators rely on these reports, environmental impact assessments must be based on rigorous and transparent analysis.

Optical microalgal biosensors for aqueous contaminants using organically doped silica as cellular hosts.

Optical biosensors for the detection of toxic species in aqueous media were developed via the encapsulation of microalgae in sol-gel matrices. In a first step, the effect of cadmium(II), lead(II), and anthracene on the chlorophyll a fluorescence intensity of Anabaena flos-aquae, Chlorella vulgaris, and Euglena gracilis microalgae in suspension was studied. Complementary ATP-metry measurements demonstrated a direct relationship between optical response and pollutant toxicity, in a cell- and dose-dependent manner. In a second step, microalgae were successfully encapsulated in silicate-colloidal silica nanocomposite matrices. However, a complete loss of cell response to pollutant addition was observed, despite the preservation of cell viability. Introduction of a low amount (5 mol%) of amine- or ethyl-bearing silanes in the matrix formulation allowed the recovery of the sensing capacity of the immobilized microalgae, without impacting on the response time (30 s). Porosimetry and 29Si solid-state NMR spectroscopy showed that the organic moieties are fully integrated into the inorganic network, tuning the ability of the target pollutant to diffuse and reach the encapsulated algae. This versatile strategy could be useful for the easy and fast assessment of contamination levels in polluted waters. Graphical Abstract Microalgal biosensors for aqueous contaminants using organically doped silica as cellular hosts.

Digital Holography as Computer Vision Position Sensor with an Extended Range of Working Distances.

Standard computer vision methods are usually based on powerful contact-less measurement approaches but applications, especially at the micro-scale, are restricted by finite depth-of-field and fixed working distance of imaging devices. Digital holography is a lensless, indirect imaging method recording the optical wave diffracted by the object onto the image sensor. The object is reconstructed numerically by propagating the recorded wavefront backward. The object distance becomes a computation parameter that can be chosen arbitrarily and adjusted to match the object position. No refractive lens is used and usual depth-of-field and working distance limitations are replaced by less restrictive ones tied to the laser-source coherence-length and to the size and resolution of the camera sensor. This paper applies digital holography to artificial visual in-plane position sensing with an extra-large range-to-resolution ratio. The object is made of a pseudoperiodic pattern allowing a subpixel resolution as well as a supra field-of-observation displacement range. We demonstrate an in-plane resolution of 50 nm and 0.002deg. in X, Y and θ respectively, over a working distance range of more than 15 cm. The allowed workspace extends over 12×10×150mm3. Digital holography extends the field of application of computer vision by allowing an extra-large range of working distances inaccessible to refractive imaging systems.

The Insignificance of Thresholds in Environmental Impact Assessment: An Illustrative Case Study in Canada.

Environmental assessment is the process that decision-makers rely on to predict, evaluate, and prevent biophysical, social, and economic impacts of potential project developments. The determination of significance in environmental assessment is central to environmental management in many nations. We reviewed ten recent environmental impact assessments from British Columbia, Canada and systematically reviewed and scored significance determination and the approaches used by assessors, the use of thresholds in significance determination, threshold exceedances, and the outcomes. Findings of significant impacts were exceedingly rare and practitioners used a combination of significance determination approaches, most commonly relying upon reasoned argumentation. Quantitative thresholds were rarely employed, with less than 10% of the valued components evaluated using thresholds. Even where quantitative thresholds for significance were exceeded, in every case practitioners used a variety of rationales to demote negative impacts to non-significance. These reasons include combinations of scale (temporal and spatial) of impacts, an already exceeded baseline, model uncertainty and/or substituting less stringent thresholds. Governments and agencies can better protect resources by requiring clear and defensible significance determinations, by making government-defined thresholds legally enforceable and accountable, and by requiring or encouraging significance determination through inclusive and collaborative approaches.

How High Concentrations of Proteins Stabilize the Amorphous State of Calcium Orthophosphate: A Solid-State Nuclear Magnetic Resonance (NMR) Study of the Casein Case.

Understanding how proteins stabilize amorphous calcium ortho-phosphate (ACP) phases is of great importance in biology and for pharmaceutical or food applications. Until now, most of the former investigations about ACP-protein stability and equilibrium were performed under conditions where ACP colloidal nanoclusters are surrounded by low to moderate concentrations of peptides or proteins (15-30 g L-1). As a result, the question of ACP-protein interactions in highly concentrated protein systems has clearly been overlooked, whereas it corresponds to actual industrial conditions such as drying or membrane filtration in the dairy industry for instance. In this study, the structure of an ACP phase is monitored in association with one model phosphorylated protein (casein) using solid-state nuclear magnetic resonance (ssNMR) under two conditions of high protein concentration (300 and 400 g L-1). At both concentrations and at 25 °C, it is found that the caseins maintain the mineral phase in an amorphous form with no detectable influence on its structure or size. Interestingly, and in both cases, a significant amount of the nonphosphorylated side chains interacts with ACP through hydrogen bonds. The number of these interacting side chains is found to be higher at the highest casein concentration. At 45 °C, which is a destabilizing temperature of ACP under protein-free conditions, the amorphous structure of the mineral phase is partially transformed at a casein concentration of 300 g L-1, while it remains almost intact at a casein concentration of 400 g L-1. Therefore, these results clearly indicate that increasing the concentration of proteins favors ACP-protein interactions and stabilizes the ACP clusters more efficiently.

Barriers to the development of forest carbon offsetting: Insights from British Columbia, Canada.

In recent years, the provision of economic incentives through carbon financing and carbon offsetting has been central to efforts at forest carbon mitigation. However, notwithstanding their potentially important roles in climate policy, forest carbon offsets face numerous barriers which have limited widespread implementation worldwide. This paper uses the case study of the Canadian province of British Columbia to explore the barriers associated with achieving widespread implementation of forest carbon offsets in the next several decades. Drawing on interviews with experts from government, non-governmental organizations, the private sector and First Nations, six main barriers are identified and discussed: (1) deficiencies of carbon markets, (2) limited economic benefits, (3) uncertain climate effectiveness, (4) negative public opinion, (5) limited and uncertain property rights, and (6) governance issues. While respondents from different sectors agreed on various points, divergence was also observed, notably on the trade-off between generating environmentally sound offsets and promoting cost-effective ways to achieve mitigation. We discuss these differences in the context of the goals and objectives of different actors, and offer insights for understanding the uptake (or not) of carbon offset policies.

Photoluminescence spectra and quantum yields of gold nanosphere monomers and dimers in aqueous suspension.

The intrinsic one-photon excited photoluminescence (PL) of dimers and monomers of gold spheres suspended in water was studied by combining photon time-of-flight spectroscopy (PTOFS) and light scattering fluctuation correlation spectroscopy (LS-FCS). The samples are obtained by precisely controlling the dimerization of aqueous colloidal systems based on 50 and 80 nm gold nanospheres. The combination of PTOFS and LS-FCS enables the separate spectroscopic study of monomers and dimers even though they exist as a mixture in the samples. PL emission spectra and diffusional dynamics are obtained simultaneously through measurement at the single particle level. The PL spectra resemble the light scattering spectra, indicating the plasmon-assisted character of the photoluminescence process. We determine the intrinsic PL quantum yields of the dimers and the monomers. It is often not possible to measure such very low quantum yields in solution using conventional techniques, and we show here that PTOFS provides access to this information. The quantum yield of the dimers was found to be of same order of magnitude as that of the monomers, of the order of 10-6, which indicates that the interparticle 'electromagnetic hot-spots' do not play a major role in the luminescence emission mechanism in such plasmonic molecules.

High-energy, kHz, picosecond hybrid Yb-doped chirped-pulse amplifier.

We report on a diode-pumped, hybrid Yb-doped chirped-pulse amplification (CPA) laser system with a compact pulse stretcher and compressor, consisting of Yb-doped fiber preamplifiers, a room-temperature Yb:KYW regenerative amplifier (RGA), and cryogenic Yb:YAG multi-pass amplifiers. The RGA provides a relatively broad amplification bandwidth and thereby a long pulse duration to mitigate B-integral in the CPA chain. The ~1030-nm laser pulses are amplified up to 70 mJ at 1-kHz repetition rate, currently limited by available optics apertures, and then compressed to ~6 ps with high efficiency. The near-diffraction-limited beam focusing quality is demonstrated with M(x)(2) = 1.1 and M(y)(2) = 1.2. The shot-to-shot energy fluctuation is as low as ~1% (rms), and the long-term energy drift and beam pointing stability for over 8 hours measurement are ~3.5% and <6 µrad (rms), respectively. To the best of our knowledge, this hybrid laser system produces the most energetic picosecond pulses at kHz repetition rates among rod-type laser amplifiers. With an optically synchronized Ti:sapphire seed laser, it provides a versatile platform optimized for pumping optical parametric chirped-pulse amplification systems as well as driving inverse Compton scattered X-rays.

Identification of a previously unobserved dissociative ionization pathway in time-resolved photospectroscopy of the deuterium molecule.

A femtosecond vacuum ultraviolet (VUV) pulse with high spectral resolution (<200 meV) is selected from the laser-driven high order harmonics. This ultrafast VUV pulse is synchronized with an infrared (IR) laser pulse to study dissociative ionization in deuterium molecules. At a VUV photon energy of 16.95 eV, a previously unobserved bond-breaking pathway is found in which the dissociation direction does not follow the IR polarization. We interpret it as corresponding to molecules predissociating into two separated atoms, one of which is photoionized by the following IR pulse. A time resolved study allows us to determine the lifetime of the intermediate predissociation process to be about 1 ps. Additionally, the dissociative ionization pathways show high sensitivity to the VUV photon energy. As the VUV photon energy is blueshifted to 17.45 eV, the more familiar bond-softening channel is opened to compete with the newly discovered pathway. The interpretation of different pathways is supported by the energy sharing between the electron and nuclei.

Impact of Polyethylenimine Conjugation Mode on the Cell Transfection Efficiency of Silica Nanovectors.

The conjugation of polyethylenimine (PEI) to silica nanoparticles has emerged as a useful strategy in gene delivery. Here we investigate the influence of the PEI conjugation mode on the transfection ability of plain silica nanoparticles. Surface functionalization with sulfonate- and chloride-bearing silanes modulates the amount and conformation of PEI and therefore the particles' affinity for the plasmid, without impacting on cytotoxicity. However, transfection efficiency in both immortalized and primary cells is more directly correlated to the nature and strength of the particle-PEI interactions. It suggests that PEI detachment from the particle surface at the stage of endosomal escape is a key event in the plasmid delivery process. These data should provide fruitful guidelines for the fine tuning of colloidal surfaces intended for intracellular delivery of bioactive molecules.

Nanostructured ultrafast silicon-tip optical field-emitter arrays.

Femtosecond ultrabright electron sources with spatially structured emission are an enabling technology for free-electron lasers, compact coherent X-ray sources, electron diffractive imaging, and attosecond science. In this work, we report the design, modeling, fabrication, and experimental characterization of a novel ultrafast optical field emission cathode comprised of a large (>100,000 tips), dense (4.6 million tips·cm(-2)), and highly uniform (<1 nm tip radius deviation) array of nanosharp high-aspect-ratio silicon columns. Such field emitters offer an attractive alternative to UV photocathodes while providing a direct means of structuring the emitted electron beam. Detailed measurements and simulations show pC electron bunches can be generated in the multiphoton and tunneling regime within a single optical cycle, enabling significant advances in electron diffractive imaging and coherent X-ray sources on a subfemtosecond time scale, not possible before. At high charge emission yields, a slow rollover in charge is explained as a combination of the onset of tunneling emission and the formation of a virtual cathode.