Penerapan Metode Pembelajaran Numbered Heads Together (Nht) Untuk Meningkatkan Motivasi Dan Hasil Belajar Kelarutan Dan Hasil Kali Kelarutan Kelas XI IPA 4 Sman 8 Surakarta Tahun Pelajaran 2012/2013

Tujuan penelitian ini adalah untuk meningkatkan (1) motivasi belajar kelarutan dan hasil kali kelarutan dan (2) hasil belajar kelarutan dan hasil kali kelarutan melalui penerapan metode pembelajaran Numbered Heads Together (NHT). Penelitian ini merupakan penelitian tindakan kelas (Classroom Action Research) yang dilaksanakan dalam dua siklus dimana setiap siklusnya terdiri atas empat tahapan, yaitu perencanaan, pelaksanaan, pengamatan, dan refleksi. Subjek penelitian adalah siswa kelas XI IPA 4 SMAN 8 Surakarta Tahun Pelajaran 2012/2013. Pengumpulan data dilakukan melalui pengamatan, wawancara, kajian dokumen, angket, dan tes. Data yang diperoleh divalidasi menggunakan teknik triangulasi sumber dan dianalisis menggunakan analisis deskriptif kualitatif yang mengacu pada Miles dan Huberman. Hasil penelitian menunjukkan capaian motivasi belajar pada siklus I dan siklus II masing-masing mencapai 58,33% dan 79,17%. Hasil belajar yang diukur pada aspek kognitif dan afektif menunjukkan pada siklus I mencapai 29,17% dan 62,5% serta pada siklus II mencapai 70,83% dan 83,33%. Simpulan penelitian ini adalah penerapan metode pembelajaran Numbered Heads Together (NHT) mampu meningkatkan (1) motivasi belajar kelarutan dan hasil kali kelarutan dan (2) hasil belajar kelarutan dan hasil kali kelarutan kelas XI IPA 4 SMAN 8 Surakarta

Self-Bridging of Vertical Silicon Nanowires and a Universal Capacitive Force Model for Spontaneous Attraction in Nanostructures

Spontaneous attractions between free-standing nanostructures have often caused adhesion or stiction that affects a wide range of nanoscale devices, particularly nano/microelectromechanical systems. Previous understandings of the attraction mechanisms have included capillary force, van der Waals/Casimir forces, and surface polar charges. However, none of these mechanisms universally applies to simple semiconductor structures such as silicon nanowire arrays that often exhibit bunching or adhesions. Here we propose a simple capacitive force model to quantitatively study the universal spontaneous attraction that often causes stiction among semiconductor or metallic nanostructures such as vertical nanowire arrays with inevitably nonuniform size variations due to fabrication. When nanostructures are uniform in size, they share the same substrate potential. The presence of slight size differences will break the symmetry in the capacitive network formed between the nanowires, substrate, and their environment, giving rise to electrostatic attraction forces due to the relative potential difference between neighboring wires. Our model is experimentally verified using arrays of vertical silicon nanowire pairs with varied spacing, diameter, and size differences. Threshold nanowire spacing, diameter, or size difference between the nearest neighbors has been identified beyond which the nanowires start to exhibit spontaneous attraction that leads to bridging when electrostatic forces overcome elastic restoration forces. This work illustrates a universal understanding of spontaneous attraction that will impact the design, fabrication, and reliable operation of nanoscale devices and systems

III−V Nanowire Growth Mechanism: V/III Ratio and Temperature Effects

We have studied the dependence of Au-assisted InAs nanowire (NW) growth on InAs(111)B substrates as a function of substrate temperature and input V/III precursor ratio using organometallic vapor-phase epitaxy. Temperature-dependent growth was observed within certain temperature windows that are highly dependent on input V/III ratios. This dependence was found to be a direct consequence of the drop in NW nucleation and growth rate with increasing V/III ratio at a constant growth temperature due to depletion of indium at the NW growth sites. The growth rate was found to be determined by the local V/III ratio, which is dependent on the input precursor flow rates, growth temperature, and substrate decomposition. These studies advance understanding of the key processes involved in III−V NW growth, support the general validity of the vapor−liquid−solid growth mechanism for III−V NWs, and improve rational control over their growth morphology

Shape-Controlled Synthesis of MnO₂ Nanostructures with Enhanced Electrocatalytic Activity for Oxygen Reduction

In this work, three types of MnO2 nanostructures, viz., microsphere/nanosheet core−corona hierarchical architectures, one-dimensional (1D) nanorods, and nanotubes, have been synthesized employing a simple hydrothermal process. The formation mechanisms have been rationalized. The materials have been thoroughly characterized by X-ray diffraction, Brunauer−Emmett−Teller spectrometry, field-emission scanning electron miscroscopy, energy dispersive spectroscopy, and transmission electron microscopy. The microsphere/nanosheet core−corona hierarchical structures are found to be the layered birnessite-type MnO2, while 1D nanorods and nanotubes are of the α-MnO2 phase. These MnO2 nanostructures are used as a model system for studying the shape/phase-dependent electrocatalytic properties for the oxygen reduction reaction, which have be investigated by cyclic and linear sweep voltammetry. It is found that α-MnO2 nanorods/tubes possess largely enhanced electrocatalytic activity compared to birnessite-type MnO2 core−corona spheres despite the latter having a much higher specific surface area. The vast difference in electrocatalytic activity is discussed in terms of crystal structure, oxygen adsorption mode, and exposed crystal facets

Data for: Increasing hypoxia in the Changjiang Estuary during the last three decades deciphered from sedimentary redox-sensitive elements

Table S1 Minimum DO concentrations and hypoxic areas (≤2 mg l-1) off the Changjiang Estuary Table S2 Grain size data for sediment cores. Table S3 Geochemical data for sediment cores. Table S4 Accuracy of measured elements in certified reference materials Table S5 Correlation coefficients between RSEs/Al and major control factor

Surface Diffusion and Substrate−Nanowire Adatom Exchange in InAs Nanowire Growth

We report new fundamental insights into InAs nanowire (NW) nucleation and evolution on InAs (111)B surfaces using organometallic vapor phase epitaxy and present the first experimental demonstration of two distinct NW growth regimes, defined by the direction of substrate−NW adatom exchange, that lead to nonlinear growth rates. We show that the NW elongation rate and morphology in these two growth regimes are governed by the relative difference between the In adatom diffusion lengths on the growth substrate surface and on the NW sidewalls, resulting in strong growth rate dependence on the NW length. These results indicate that surface solid−phase diffusion of In adatoms is a key process in InAs NW growth, which is also supported by diameter-dependent growth rates. These developments enable rational growth of axial and radial NW heterostructures

Growth of InAs Nanowires on SiO₂ Substrates: Nucleation, Evolution, and the Role of Au Nanoparticles

We have studied the nucleation and growth of InAs nanowires (NWs) on SiO2/Si substrates by organometallic vapor-phase epitaxy (OMVPE). Through systematic characterization of InAs NW morphology as a function of V/III precursor ratio, precursor flow rates, growth temperature, growth time, and the presence/absence of Au nanoparticles, a number of significant insights into InAs NW growth using OMVPE have been developed. Specifically, we have found that (i) the growth of InAs NWs can be initiated from a single indium (In) droplet, (ii) Au nanoparticles (NPs) enhance group V precursor (AsH3) pyrolysis but are not necessary to nucleate growth, (iii) growth of InAs NWs on SiO2 substrates occurs in the kinetically limited vapor−liquid−solid (VLS) growth regime, (iv) InAs NWs on SiO2 films decompose at elevated temperatures even under significant AsH3 overpressure, and (v) the V/III ratio is the growth-rate-limiting factor in the VLS growth of the InAs nanowires. Many of these findings on InAs NW growth can be generalized to and provide very useful information for rational synthesis of other III−V compound semiconductor NWs

Seasonal dynamics of (A, B, and C) soil moisture (V/V%) and (D, E, and F) soil temperature (°C) at 0–10 cm depth in 2012, 2013, and 2014.

<p>CK: control; W: water addition; N: nitrogen addition; WN: water and nitrogen added in combination. Data are reported as mean ± 1 SD (<i>n</i> = 6).</p

Positive dependence of growing season mean (A) net ecosystem CO₂ exchange (NEE, μmol m^-2 s^-1), (B) ecosystem respiration (ER, μmol m^-2 s^-1) and (C) gross ecosystem productivity (GEP, μmol m^-2 s^-1) on the amount of early growing season (Apr, May, Jun) precipitation (water added + natural precipitation) across the 3 years in both fertilized (open circles) and unfertilized plots (solid circles).

<p>Nitrogen fertilized plots include both the N and WN plots, and unfertilized plots include both the CK and W plots. Water addition was treated as a precipitation event and included in the calculation of the precipitation amount. * and ** represent significant relationships at the <i>P</i> < 0.05 and <i>P</i> < 0.01 levels, respectively.</p

A Systematic Study on the Growth of GaAs Nanowires by Metal−Organic Chemical Vapor Deposition

The epitaxial growth of GaAs nanowires (NWs) on GaAs(111)B substrates by metal−organic chemical vapor deposition has been systematically investigated as a function of relevant growth parameters, namely, temperature, arsine (AsH3) and trimethyl-gallium (TMGa) flow rates, growth time, and gold nanoparticle catalyst size. When growing in excess As conditions (V/III molar ratios greater than four), the NW growth rate is independent of AsH3 concentration, while it is linearly dependent on TMGa concentration, and it is thermally activated. The NW morphology is primarily affected by the growth temperature, with very uniform NWs growing at around 400 °C and severely tapered NWs growing above 500 °C. A simple phenomenological expression that allows prediction of the NW growth rate over a wide range of growth parameters has been derived. The growth rate dependence on the seed nanoparticle size has also been investigated, which reveals valuable information on the role of catalyst supersaturation and Ga surface diffusion in the growth mechanism. The NW growth rate is found to be almost independent of Au nanoparticle size down to diameters of ∼20 nm over a wide range of temperatures and TMGa and AsH3 molar flows. For smaller NW radii, the growth rate becomes size-dependent and is strongly affected by the V/III molar ratio; at relatively low V/III ratios, smaller NWs grow more slowly due to the Gibbs−Thompson effect, while at higher V/III ratios (V/III > 50), Ga adatom diffusion becomes the dominant mass-transport mechanism, and smaller NWs grow faster than larger ones. The growth-limiting mechanisms in the above growth regimes are finally discussed, and important quantities such as pyrolysis efficiency of the precursors, supersaturation, and surface diffusion length are deduced by comparing the experimental results with the NW growth rates predicted from first principles