184 research outputs found
Stability of an oscillating tip in Non-Contact Atomic Force Microscopy: theoretical and numerical investigations
This paper is a theoretical and a numerical investigation of the stability of
a tip-cantilever system used in Non-Contact Atomic Force Microscopy (NC-AFM)
when it oscillates close to a surface. No additional dissipative force is
considered. The theoretical approach is based on a variationnal method
exploiting a coarse grained operation that gives the temporal dependence of the
nonlinear coupled equations of motion in amplitude and phase of the oscillator.
Stability criterions for the resonance peak are deduced and predict a stable
behavior of the oscillator in the vicinity of the resonance. The numerical
approach is based on results obtained with a virtual NC-AFM developped in our
group. The effect of the size of the stable domain in phase is investigated.
These results are in particularly good agreement with the theoretical
predictions. Also they show the influence of the phase shifter in the feedback
loop and the way it can affect the damping signal
POLA PENGGUNAAN OBAT PADA PASIEN STROKE HEMORAGIK DI RSUP PROF. DR. R.D. KANDOU MANADO PERIODE JANUARI-DESEMBER 2018
ABSTRACK Hemorrhagic stroke is a stroke caused by intracerebral hemorrhage or subarachniod hemorrhage due to rupture of cerebral blood vessels in certain areas, so that blood fills the brain tissue. The selection and use of drugs must be rational, so that treatment can achieve maximum therapy with minimal side effects. The purpose of this study was to determine the characteristics and patterns of drug use in hemorrhagic stroke patients at Prof. RSUP Dr. R.D. Kandou Manado. This study uses a descriptive method with a retrospective research design. The sample of this study were 83 patients, including 70 intracerebral hemorrhagic stroke patients and 13 subarachnoid hemorrhagic stroke patients. Patient characteristics were mostly male as many as 46 patients (55.42%) and female as many as 37 patients (44.58%). The largest age range of hemorrhagic stroke patients at the age of 55-64 years was 27 patients (32.52%). The duration of treatment with the highest prevalence was 1-5 days in 37 patients (44.57%). Hypertension is the most common comorbid disease of 60 patients (40.27%), and cholesterol of 15 patients (10.06). The pattern of drug use based on the evaluation of the right indication as many as 83 patients (100%), the right patients as many as 83 patients (100%), the right drugs as many as 82 patients (98.8%), and the right dosage of 73 patients (87.95%). Keywords: Hemorrhagic stroke, drug use ABSTRAK Stroke hemoragik adalah stroke yang disebabkan oleh perdarahan intraserebral atau perdarahan subarakhniod karena pecahnya pembuluh darah otak pada area tertentu, sehingga darah memenuhi jaringan otak. Pemilihan dan penggunaan obat harus secara rasional, sehingga pengobatan dapat mencapai terapi yang maksimal dengan efek samping minimal. Tujuan dari penelitian ini untuk mengetahui karakteristik dan pola penggunaan obat pada pasien stroke hemoragik di RSUP Prof. Dr. R.D. Kandou Manado. Penelitian ini menggunakan metode deskriptif dengan desain penelitian retrospektif. Sampel penelitian ini sebanyak 83 pasien, diantaranya terdapat 70 pasien stroke hemoragik intraserebral dan 13 pasien stroke hemoragik subarakhnoid. Karakteristik pasien sebagian besar adalah laki-laki sebanyak 46 pasien (55,42%) dan perempuan sebanyak 37 pasien (44,58%). Rentang usia pasien stroke hemoragik terbesar pada usia 55-64 tahun sebanyak 27 pasien (32,52%). Lama perawatan dengan prevalensi paling banyak, yaitu 1 – 5 hari pada 37 pasien (44,57%). Hipertensi merupakan penyakit penyerta yang paling banyak diderita sebesar 60 pasien (40,27%), dan kolestrol sebanyak 15 pasien (10,06). Pola penggunaan obat berdasarkan evaluasi tepat indikasi sebanyak 83 pasien (100%), tepat pasien sebanyak 83 pasien (100%), tepat obat sebanyak 82 pasien (98,8%), dan tepat dosis sebanyak 73 pasien (87,95%). Kata kunci : stroke hemoragik, pola penggunaan oba
Distance dependence of force and dissipation in non-contact atomic force microscopy on Cu(100) and Al(111)
The dynamic characteristics of a tip oscillating in the nc-AFM mode in close
vicinity to a Cu(100)-surface are investigated by means of phase variation
experiments in the constant amplitude mode. The change of the quality factor
upon approaching the surface deduced from both frequency shift and excitation
versus phase curves yield to consistent values. The optimum phase is found to
be independent of distance. The dependence of the quality factor on distance is
related to 'true' damping, because artefacts related to phase misadjustment can
be excluded. The experimental results, as well as on-resonance measurements at
different bias voltages on an Al(111) surface, are compared to Joule
dissipation and to a model of dissipation in which long-range forces lead to
viscoelastic deformations
Temperature dependence of the energy dissipation in dynamic force microscopy
The dissipation of energy in dynamic force microscopy is usually described in
terms of an adhesion hysteresis mechanism. This mechanism should become less
efficient with increasing temperature. To verify this prediction we have
measured topography and dissipation data with dynamic force microscopy in the
temperature range from 100 K up to 300 K. We used
3,4,9,10-perylenetetracarboxylic-dianhydride (PTCDA) grown on KBr(001), both
materials exhibiting a strong dissipation signal at large frequency shifts. At
room temperature, the energy dissipated into the sample (or tip) is 1.9
eV/cycle for PTCDA and 2.7 eV/cycle for KBr, respectively, and is in good
agreement with an adhesion hysteresis mechanism. The energy dissipation over
the PTCDA surface decreases with increasing temperature yielding a negative
temperature coefficient. For the KBr substrate, we find the opposite behaviour:
an increase of dissipated energy with increasing temperature. While the
negative temperature coefficient in case of PTCDA agrees rather well with the
adhesion hysteresis model, the positive slope found for KBr points to a
hitherto unknown dissipation mechanism
Influence of noncontact dissipation in the tapping mode: Attempt to extract quantitative information on the surface properties with the local force probe method
In the Tapping mode, a variation of the oscillation amplitude and phase as a
function of the tip sample distance is the necessary measurement to access
quantitatively to the properties of the surface. In the present work, we give a
systematic comparison between experimental data recorded on two surfaces, phase
and amplitude, and theoretical curves. With an interaction between the tip and
the surface taking into account an attractive and a repulsive term, the
analytical approach is unable to properly describe the relationship between the
phase variation and the oscillation amplitude variation. When an additional
dissipation term is involved, due to the attractive interaction between the tip
and the surface, the model gives a good agreement with the recorded data.
Particularly, the trends in the phase variations related to the noncontact
situations have been found to be amenable to an analysis based upon a simple
viscoelastic behavior of the surface
Dynamic condensation of water at crack tips in fused silica glass
Water molecules play a fundamental role in the physics of slow crack
propagation in glasses. It is commonly understood that, during
stress-corrosion, water molecules that move in the crack cavity effectively
reduce the bond strength at the strained crack tip and, thus, support crack
propagation. Yet the details of the environmental condition at the crack tip in
moist air are not well determined. In a previous work, we reported direct
evidence of the presence of a 100 nm long liquid condensate at the crack tip in
fused silica glass during very slow crack propagation (10^-9 to 10^-10 m/s).
These observations are based on in-situ AFM phase imaging techniques applied on
DCDC glass specimens in controlled atmosphere. Here, we discuss the physical
origin of the AFM phase contrast between the liquid condensate and the glass
surface in relation to tip-sample adhesion induced by capillary bridges. We
then report new experimental data on the water condensation length increase
with relative humidity in the atmosphere. The measured condensation lengths
were much larger than what predicted using the Kelvin equation and expected
geometry of the crack tip.Comment: Accepted in JNCS. In pres
Analytical Approach to the Local Contact Potential Difference on (001) Ionic Surfaces: Implications for Kelvin Probe Force Microscopy
An analytical model of the electrostatic force between the tip of a
non-contact Atomic Force Microscope (nc-AFM) and the (001) surface of an ionic
crystal is reported. The model is able to account for the atomic contrast of
the local contact potential difference (CPD) observed while nc-AFM-based Kelvin
Probe Force Microscopy (KPFM) experiments. With the goal in mind to put in
evidence this short-range electrostatic force, the Madelung potential arising
at the surface of the ionic crystal is primarily derived. The expression of the
force which is deduced can be split into two major contributions: the first
stands for the coupling between the microscopic structure of the tip apex and
the capacitor formed between the tip, the ionic crystal and the
counter-electrode; the second term depicts the influence of the Madelung
surface potential on the mesoscopic part of the tip, independently from its
microscopic structure. These short-range electrostatic forces are in the range
of ten pico-Newtons. When explicitly considering the crystal polarization, an
analytical expression of the bias voltage to be applied on the tip to
compensate for the local CPD, i.e. to cancel the short-range electrostatic
force, is derived. The compensated CPD has the lateral periodicity of the
Madelung surface potential. However, the strong dependence on the tip geometry,
the applied modulation voltage as well as the tip-sample distance, which can
even lead to an overestimation of the real surface potential, makes
quantitative KPFM measurements of the local CPD extremely difficult
Observation of individual molecules trapped on a nanostructured insulator
For the first time, ordered polar molecules confined in monolayer-deep
rectangular pits produced on an alkali halide surface by electron irradiation
have been resolved at room temperature by non-contact atomic force microscopy.
Molecules self-assemble in a specific fashion inside pits of width smaller than
15 nm. By contrast no ordered aggregates of molecules are observed on flat
terraces. Conclusions regarding nucleation and ordering mechanisms are drawn.
Trapping in pits as small as 2 nm opens a route to address single molecules
Canopy precipitation interception in a lowland tropical forest in relation to stand structure
It is generally accepted that vegetation provides important ecosystem services especially in term of rainfall partitioning. This study aims to evaluate the influence of canopy structure namely crown area (CA), diameter at breast height (DBH), tree height (TH) and crown spread (CS) and stand density on the partitioning of rainfall. Twelve throughfall plots of 20 x 20 m with 64 gauges randomly placed within each plot were established. For stemflow measurements, all trees within a 100 m2 plot within the study area were collared. Interception loss was computed as the difference between precipitation and throughfall plus stemflow. Throughfall ranged from 73.47 - 82.32 % of the gross rainfall. Stemflow was found to be roughly around 2.01% of the gross rainfall. Highest interception was 24.52 % attributed to the plot having the highest above ground biomass (AGB) density. The relation between canopy interception and forest structure were analyzed by regression method. Multiple regression analysis on the potential influence of stand structure to the throughfall percentage shows that all the forest structures variables measured in this study are negatively correlated to the amount of throughfall generated. This study suggests that forests with higher value of DBH, CA, CS and TH had higher interception rate
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