General Strategies for Nanoparticle Dispersion Mackay, Michael E; Tuteja, Anish; Duxbury, Phillip M ...
Science (American Association for the Advancement of Science),
03/2006, Letnik:
311, Številka:
5768
Journal Article
Recenzirano
Traditionally the dispersion of particles in polymeric materials has proven difficult and frequently results in phase separation and agglomeration. We show that thermodynamically stable dispersion of ...nanoparticles into a polymeric liquid is enhanced for systems where the radius of gyration of the linear polymer is greater than the radius of the nanoparticle. Dispersed nanoparticles swell the linear polymer chains, resulting in a polymer radius of gyration that grows with the nanoparticle volume fraction. It is proposed that this entropically unfavorable process is offset by an enthalpy gain due to an increase in molecular contacts at dispersed nanoparticle surfaces as compared with the surfaces of phase-separated nanoparticles. Even when the dispersed state is thermodynamically stable, it may be inaccessible unless the correct processing strategy is adopted, which is particularly important for the case of fullerene dispersion into linear polymers.
► Adsorbent for Ni(II) removal prepared from raw sugarcane bagasse pith. ► Activated carbon (SBP-AC) characterized and batch adsorption studies performed. ► Maximum adsorption occurred at pH 6.5. ► ...Adsorption mechanism is controlled by pH, Ni(II) speciation and pHzpc of SBP-AC. ► Desorption studies were performed to evaluate adsorbent efficiency.
Bioavailability of Nickel in the form of hydrated Nickel(II) attributes to its toxicological effects and hence its removal from aqueous solution is of great concern. Adsorption is used as an efficient technique for the removal of Nickel(II), hereafter Ni(II), from water and wastewaters. Activated carbon obtained from sugarcane bagasse pith (SBP-AC), a waste biomass collected from juice shops in Sarkara Devi Temple, Chirayinkeezhu, Trivandrum, India during annual festival, is used as adsorbent in the study. The process of adsorption is highly dependent on solution pH, and maximum removal occurs in the pH range of 4.0–8.0. Moreover, the amount of Ni(II) adsorbed onto SBP-AC increased with the time increase and reached equilibrium at 4h. Adsorption kinetic and equilibrium data were analyzed for determining the best fit kinetic and isotherm models. The overall study reveals the potential value of steam pyrolysed SBP-AC as a possible commercial adsorbent in wastewater treatment strategies.
Alkali metal dimers attached to the surface of helium nanodroplets are found to be efficiently doubly ionized by electron transfer mediated decay (ETMD) when photoionizing the helium droplets. This ...process is evidenced by detecting in coincidence two energetic ions created by Coulomb explosion and one low-kinetic energy electron. The kinetic energy spectra of ions and electrons are reproduced by simple model calculations based on diatomic potential energy curves, and are in agreement with
ab initio
calculations for the He-Na
2
and He-KRb systems. This work demonstrates that ETMD is an important decay channel in heterogeneous nanosystems exposed to ionizing radiation.
Double ionization of alkali dimers attached to He nanodroplets by electron transfer mediated decay (ETMD).
•Experiments and two-zone modeling studies in natural gas/diesel HDDI engine.•Increasing methane concentration increases ISEC, CO and max pressure.•Increasing methane concentration reduces NO and ...soot.•Advancing diesel fuel injection timing reduces ISEC, CO and soot.•Advancing diesel fuel injection timing increases max pressure and NO.
Diesel engines find widespread applications in stationary and transportation systems owing to their high fuel efficiency, high torque output, and great size flexibility. However, they still constitute major polluting sources, especially regarding NO and particulate emissions. Therefore, more conventional diesel engines internationally are pursuing the option of conversion to using natural gas as a supplement fuel for the conventional diesel fuel. Many research studies carried out in the aforementioned research field have shown that the specific engine operating mode, in comparison to the conventional diesel one, suffers from higher specific fuel consumption and CO emission. The diesel fuel injection timing and the proportion of the gaseous fuel influence significantly the combustion mechanism, with this effect becoming more evident at part load conditions. Thus, in order to examine the effect of these two parameters on the performance and exhaust emissions, a combined experimental and theoretical investigation is conducted herein on a single-cylinder research, dual fuel (diesel-natural gas), HDDI compression ignition engine. Specifically, through the experimental investigation the effect of diesel fuel injection timing is examined on the performance and exhaust emissions of the engine operating under part load and constant natural gas/diesel mass ratio conditions. Moreover, following validation of the latter, theoretical results concerning the combined effects of both parameters of diesel fuel injection timing and natural gas/diesel mass ratio on the performance and exhaust emissions characteristics of the engine operating at two different loading conditions are obtained, via the application of an in-house, comprehensive, two-zone phenomenological model. The main objective of this assessment is to record and comparatively evaluate the relative impact of these parameters for part and high engine loading conditions. From the experimental and theoretical findings, it is revealed that for the examined test engine operating under constant natural gas/diesel mass ratio, a restricted increase in the diesel fuel injection timing could be a promising solution for engine efficiency improvement and CO emission mitigation, while simultaneously it seemed to increase NO emissions. For extremely advanced diesel fuel injection timing, a simultaneous variation of natural gas/diesel mass ratio at both engine loading conditions could cause problems to the engine structure because, in those cases, the maximum cylinder pressure becomes considerable and hence possibly harmful to the engine structural integrity. The information derived from the present work is valuable, especially if one wishes to define the optimum combination of examined strategies for improving the behavior of an existing engine running under natural gas/diesel operating mode.
In bulk materials, defects are usually considered to be unwanted since deviations from perfect lattices may degrade device performance. Interestingly, the presence of defects throws open new ...possibilities in the case of nanostructures due to the properties related to their limited size scale. Defects and disorders which alter the electronic structure of nanostructures can significantly influence their electronic, magnetic and nonlinear optical properties. Here, we show that defect engineering is an effective strategy for tailoring the nonlinear optical (NLO) properties of carbon and ZnO nanostructures. The effects of surface states, lattice disorders, polycrystalline interfaces and heterogeneous dopants on the nonlinear absorption behaviour of these nanostructures are discussed in detail. Realistic tunable NLO features achieved by controlling such defects enhance the scope of these nanostructures in device applications such as optical limiting, optical switching, pulse shaping, pulse compression and optical diode action.
In bulk materials, defects are usually considered to be unwanted since deviations from perfect lattices may degrade device performance.
Transmembrane nanostructures like ion channels and transporters perform key biological functions by controlling flow of molecules across lipid bilayers. Much work has gone into engineering artificial ...nanopores and applications in selective gating of molecules, label-free detection/sensing of biomolecules and DNA sequencing have shown promise. Here, we use DNA origami to create a synthetic 9 nm wide DNA nanopore, controlled by programmable, lipidated flaps and equipped with a size-selective gating system for the translocation of macromolecules. Successful assembly and insertion of the nanopore into lipid bilayers are validated by transmission electron microscopy (TEM), while selective translocation of cargo and the pore mechanosensitivity are studied using optical methods, including single-molecule, total internal reflection fluorescence (TIRF) microscopy. Size-specific cargo translocation and oligonucleotide-triggered opening of the pore are demonstrated showing that the DNA nanopore can function as a real-time detection system for external signals, offering potential for a variety of highly parallelized sensing applications.
Prostate is the most frequent cancer in men. Prostate cancer progression is driven by androgen steroid hormones, and delayed by androgen deprivation therapy (ADT). Androgens control transcription by ...stimulating androgen receptor (AR) activity, yet also control pre-mRNA splicing through less clear mechanisms. Here we find androgens regulate splicing through AR-mediated transcriptional control of the epithelial-specific splicing regulator
. Both
and its close paralog
are highly expressed in primary prostate cancer. Androgen stimulation induces splicing switches in many endogenous ESRP2-controlled mRNA isoforms, including splicing switches correlating with disease progression.
expression in clinical prostate cancer is repressed by ADT, which may thus inadvertently dampen epithelial splice programmes. Supporting this, treatment with the AR antagonist bicalutamide (Casodex) induced mesenchymal splicing patterns of genes including
and
. Our data reveals a new mechanism of splicing control in prostate cancer with important implications for disease progression.
In this article we present a perspective on the current state of the art in the photoionization of atomic clusters in few-cycle near-infrared laser pulses. Recently, several studies have reported ...intriguing phenomena associated with the photoionization of clusters by pulses as short as ∼10 fs which approach the natural timescales of collective electronic motion in such nanoscale aggregates. In contrast to the dynamics occurring on few- and sub-picosecond timescales where ionic motion sets in and plays a key role marked by resonant plasmon oscillations, the few-cycle limit precludes cluster expansion due to the nuclear motion of ionic constituents. Thus, pulses lasting just a few optical cycles explore a new "impulsive" regime for the first time in cluster nanoplasmas wherein ions essentially remain "frozen". Along with the perspective on this new regime, we present first measurements of photoelectron distributions and temperatures.
In this article we present a perspective on the current state of the art in the photoionization of atomic clusters in few-cycle near-infrared laser pulses.
Embedded atoms or molecules in a photoexcited He nanodroplet are well-known to be ionized through inter-atomic relaxation in a Penning process. In this work, we investigate the Penning ionization of ...acetylene oligomers occurring from the photoexcitation bands of He nanodroplets. In close analogy to conventional Penning electron spectroscopy by thermal atomic collisions, the
n
= 2 photoexcitation band plays the role of the metastable atomic 1s2s
3,1
S He*. This facilitates electron spectroscopy of acetylene aggregates in the sub-Kelvin He environment, providing the following insight into their structure: the molecules in the dopant cluster are loosely bound van der Waals complexes rather than forming covalent compounds. In addition, this work reveals a Penning process stemming from the
n
= 4 band where charge-transfer from autoionized He in the droplets is known to be the dominant relaxation channel. This allows for excited states of the remnant dopant oligomer Penning-ions to be studied. Hence, we demonstrate Penning ionization electron spectroscopy of doped droplets as an effective technique for investigating dopant oligomers which are easily formed by attachment to the host cluster.
Penning spectroscopy of acetylene molecules dissolved in superfluid He nanodroplets reveals the loosely held molecular aggregate collapsing into a covalently bound oligomer ion upon indirect ionization effected by the photoexcited He* in the host.
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