599 research outputs found
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Ultrahigh Hot Carrier Transient Photocurrent in Nanocrystal Arrays by Auger Recombination.
In this report, we show that a new mechanism for carrier transport in solution-processed colloidal semiconductor nanocrystal arrays exists at high excitation intensity on ultrafast time scales and allows for facile intrinsic transport between as-prepared nanocrystals over long distances. By combining a high speed photoconductive switch with an ultrafast laser excitation in a sub-40 ps photoconductor, we observed transient photocurrents with peak densities of 3 × 104 - 106 mA/cm2 in self-assembled PbSe nanocrystals capped with long native oleic acid ligands. The ratio between the transient photocurrent peak and the steady-state dark current is 10 orders of magnitude. The transient mobility at the peak current is estimated to range between 0.5-17.5 cm2/(V s) for the various nanocrystal sizes studied, which is 6 to 9 orders of magnitude higher than the dark current steady-state mobility in PbSe, CdSe, and CdTe nanocrystals capped with native ligands. The results are analyzed using a kinetic model which attributes the ultrahigh transient photocurrent to multiple photogenerated excitons undergoing on-particle Auger recombination, followed by rapid tunneling at high energies. This mechanism is demonstrated for a wide range of PbSe nanocrystals sizes (diameters from 2.7 to 7.1 nm) and experimental parameters. Our observations indicate that native ligand-capped nanocrystal arrays are promising for optoelectronics applications wherein multiple carriers are photoinjected to interband states
Pertumbuhan Dan Produksi Kacang Bogor (Vigna Subterranea (L.) Dengan Pemberian Pupuk P Dan Arang Sekam Padi
Pemberian pupuk anorganik dan organik dapat menyediakan unsur hara yang dibutuhkan oleh tanaman kacang bogor seperti unsur hara P. Sebagian fosfor di dalam tanah umumnya tidak tersedia untuk tanaman. Salah satu bahan organik yang mampu melepaskan unsur hara P adalah arang sekam padi. Penelitian ini bertujuan untuk mengetahui respons pertumbuhan dan produksi kacang bogor terhadap pemberian pupuk P dan arang sekam padi. Penelitian dilaksanakan di lahan Fakultas Pertanian Universitas Sumatera pada Juli – Oktober 2014. Penelitian ini menggunakan Rancangan Acak Kelompok (RAK) faktorial dengan 2 faktor dan 3 ulangan. Faktor pertama yaitu pemberian pupuk P dengan 4 taraf (0; 30; 60 dan 90 kg SP-36/ha) dan faktor kedua yaitu komposisi top soil dan arang sekam padi dengan 4 taraf (1:0; 1:1; 1:2 dan 2:1). Data yang diperoleh dianalisis dengan menggunakan sidik ragam dan dilanjutkan dengan uji jarak berganda Duncan. Peubah amatan yaitu jumlah cabang, umur berbunga, bobot polong, dan bobot biji. Hasil analisis data menunjukkan bahwa pemberian pupuk P berpengaruh dalam meningkatkan jumlah cabang, umur berbunga, bobot polong dan bobot biji. Pemberian arang sekam padi meningkatkan jumlah cabang Interaksi antara pemberian pupuk P dan arang sekam padi berpengaruh tidak nyata terhadap semua peubah amatan
Theory of resonance energy transfer involving nanocrystals: the role of high multipoles
A theory for the fluorescence resonance energy transfer (FRET) between a pair
of semiconducting nanocrystal quantum dots is developed. Two types of
donor-acceptor couplings for the FRET rate are described: dipole-dipole (d-d)
and the dipole-quadrupole (d-q) coupling. The theory builds on a simple
effective mass model which is used to relate the FRET rate to measureable
quantities such as the nanocrystal size, fundamental gap, effective mass,
exciton radius and dielectric constant. We discuss the relative contribution to
the FRET rate of the different multipole terms, the role of strong to weak
confinement limits, and the effects of nanocrystal siz-es.Comment: 12 pages, 7 figure
A Fully Self-Consistent Treatment of Collective Fluctuations in Quantum Liquids
The problem of calculating collective density fluctuations in quantum liquids
is revisited. A fully quantum mechanical self-consistent treatment based on a
quantum mode-coupling theory [E. Rabani and D.R. Reichman, J. Chem. Phys.116,
6271 (2002)] is presented. The theory is compared with the maximum entropy
analytic continuation approach and with available experimental results. The
quantum mode-coupling theory provides semi-quantitative results for both short
and long time dynamics. The proper description of long time phenomena is
important in future study of problems related to the physics of glassy quantum
systems, and to the study of collective fluctuations in Bose fluids.Comment: 9 pages, 4 figure
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Resilient Pathways to Atomic Attachment of Quantum Dot Dimers and Artificial Solids from Faceted CdSe Quantum Dot Building Blocks.
The goal of this work is to identify favored pathways for preparation of defect-resilient attached wurtzite CdX (X = S, Se, Te) nanocrystals. We seek guidelines for oriented attachment of faceted nanocrystals that are most likely to yield pairs of nanocrystals with either few or no electronic defects or electronic defects that are in and of themselves desirable and stable. Using a combination of in situ high-resolution transmission electron microscopy (HRTEM) and electronic structure calculations, we evaluate the relative merits of atomic attachment of wurtzite CdSe nanocrystals on the {11Ì…00} or {112Ì…0} family of facets. Pairwise attachment on either facet can lead to perfect interfaces, provided the nanocrystal facets are perfectly flat and the angles between the nanocrystals can adjust during the assembly. Considering defective attachment, we observe for {11Ì…00} facet attachment that only one type of edge dislocation forms, creating deep hole traps. For {112Ì…0} facet attachment, we observe that four distinct types of extended defects form, some of which lead to deep hole traps whereas others only to shallow hole traps. HRTEM movies of the dislocation dynamics show that dislocations at {11Ì…00} interfaces can be removed, albeit slowly. Whereas only some extended defects at {112Ì…0} interfaces could be removed, others were trapped at the interface. Based on these insights, we identify the most resilient pathways to atomic attachment of pairs of wurtzite CdX nanocrystals and consider how these insights can translate to the creation of electronically useful materials from quantum dots with other crystal structures
Synchronization in Scale Free networks: The role of finite size effects
Synchronization problems in complex networks are very often studied by
researchers due to its many applications to various fields such as
neurobiology, e-commerce and completion of tasks. In particular, Scale Free
networks with degree distribution , are widely used in
research since they are ubiquitous in nature and other real systems. In this
paper we focus on the surface relaxation growth model in Scale Free networks
with , and study the scaling behavior of the fluctuations, in
the steady state, with the system size . We find a novel behavior of the
fluctuations characterized by a crossover between two regimes at a value of
that depends on : a logarithmic regime, found in previous
research, and a constant regime. We propose a function that describes this
crossover, which is in very good agreement with the simulations. We also find
that, for a system size above , the fluctuations decrease with
, which means that the synchronization of the system improves as
increases. We explain this crossover analyzing the role of the
network's heterogeneity produced by the system size and the exponent of the
degree distribution.Comment: 9 pages and 5 figures. Accepted in Europhysics Letter
Protein-mediated dethreading of a biotin-functionalised pseudorotaxane
In this article, we describe the synthesis of new biotin-functionalised naphthalene derivatives 3 and 4 and their complexation behaviour with avidin and neutravidin using a range of analytical techniques. We have shown using 2-(4prime or minute-hydroxyazobenzene)benzoic acid displacement and ITC experiments{,} that compounds 3 and 4 have the propensity to form reasonably high-affinity bioconjugates with avidin and neutravidin. We have also demonstrated using 1H NMR{,} UV-vis and fluorescence spectroscopy that the naphthalene moiety of 3 and 4 facilitates the formation of pseudorotaxane-like structures with 1 in water. We have then investigated the ability of avidin and neutravidin to modulate the complexation between 1 and 3 or 4. UV-vis and fluorescence spectroscopy has shown that in both cases the addition of the protein disrupts complexation between the naphthalene moieties of 3 and 4 with 1
Effect of the selected physico-chemical parameters on growth of rainbow trout (Oncorhynchus mykiss) in raceway system in Iran
A study was conducted to evaluate the correlation between selected physico-chemical parameters of water and their effects on growth of Rainbow trout (Oncorhynchus mykiss) in raceway system in the area of Sarab Gerdu, Iran. The samples were collected from twenty raceways (270-day old fish, surface area 55m^2 flow rate 150 ls^-1 total production 15 T). Physico-chemical parameters were the fluctuations of total ammonia nitrogen, dissolved oxygen, turbidity, nitrogen (nitrates), phosphorous (phosphates), total dissolved solids, electrical conductivity, fluoride, boron, pH, temperature, total hardness, and alkalinity. Multivariate analyses were conducted employing three categories of parameters including A, B, and C. The results of the study showed that temperature and pH variations were similar. Dissolved oxygen with negative similarity coefficient, _0.618 was located in the third category while positive coefficient, 0.479 of other parameters except for pH and temperature (second category) and dissolved oxygen (third category) was located in the first one. pH value was not in a standard range due to increase in water temperature. This, in turn had impact on other parameters, such as unionized ammonia, a toxic chemical, to fish. Our result demonstrated that nitrate concentration is the most significant chemical parameter for fish growth in this area. Similarity, increase in concentration of dissolved oxygen in the water (from 3.30 mgl^-1 up to 12 mgl^-1) was necessary to promote productivity
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