Characterization of a home-built low temperature scanning probe microscopy system

The continuing advancement of technology is the driving force behind science and fundamental research. Scanning probe instruments still have a major impact in nanoscience and technology, because they provide a link between the macroscopic world and the atomic scale. The key to a reliable performance of experiments at the nanometer scale is the instrumentation, that allows probe positioning ranging from micrometers to Ångstroms with sub atomic precisions. A new type of scanning probe microscopy (SPM) system operating in ultra high vacuum (UHV) and at liquid Helium (LHe) temperature was developed. This offers the advantages that even reactive surfaces remain clean over time periods of several days, permitting long time experiments. Moreover, these experiments this low temperature scanning probe microscopy (LTSPM) system is the implementation of a focussing Fabry Perot interferometer (fFPi) that allows the following features: - Small amplitude operations and stiff cantilevers require sensors with high deflection sensitivity. With the fFPi in this low temperature SPM system, a deflection sensitivity of 4fm/ sqrt(Hz) at 1MHz can be obtained. - Wide detection bandwidth (DC-10MHz) enables the operation of higher flexural oscillation modes as well as the torsional modes of the cantilever. - A laser spot size of 3µm allows the use of ultra small cantilevers with the dimensions 1/10 of conventional cantilevers. - Photothermal excitation of cantilevers avoids undesirable mechanical vibrations near the cantilever resonance frequency. - Simultaneous flexural and torsional force detection provides quantitative studies of frictions and thus, atom manipulations by atomic force microscopy (AFM). - The combination of both types of microscopes (simultaneous AFM/STM) reveals more information than a scanning tunneling microscopy (STM) or AFM alone. A series of measurements on Si(111)7x7, herringbone superstructure of Au(111) and highly oriented pyrolytic graphite (HOPG) provides information regarding imaging performance of the system. Among these performance tests are atomically resolved scans at three different operating temperatures in STM mode. In non-contact atomic force microscopy (nc-AFM) mode, imaging was performed with the cantilever driven at the fundamental and 2nd oscillation mode. Additional measurements were performed with the fFPi in order to quantify the impact of the laser cooling effects (radiation pressure and photothermal effects) on the oscillating cantilever at three different operating temperatures. The aim of this work is the development, implementation and characterization of a new low temperature scanning probe microscope with an ultra sensitive and high bandwidth fFPi deflection sensor, suitable for nc-AFM operations with small, simultaneous flexural and torsional cantilever oscillation modes. Furthermore, expected upgrades will allow simultaneous nc-AFM/STM operations. Keywords: low temperature home-built simultaneous STM/ nc-AFM, tip-sample gap stability, PLL and self-excitation, highly oriented pyrolytic graphite (HOPG), reconstructed Si(111)7x7, herringbone superstructure, focussing Fabry-Perot interferometer, cantilever cooling, radiation pressure and photothermal effects. Der kontinuierliche, technologische Fortschritt ist die treibende Kraft hinter Wissenschaft und Grundlagenforschung. Rasterkraft und -tunnel Instrumente haben immer noch einen bedeutenden Einfluss auf die Nanotechnologie und -wissenschaft, weil sie eine Verbindung zwischen der makroskopischen Welt und den atomaren Massstäben darstellen. Der Schlüssel für eine zuverlässige Ausführung von Experimenten mit Nanometer Massstäben ist die Instrumentierung, die eine Spitzenpositionierung von Mikrometer bis Ångstroms mit subatomarer Präzision erlaubt. Ein neuartiges Rasterspitzen Mikroskop (SPM) System wurde entwickelt, das im Ultra Hoch Vakuum (UHV) und bei flüssig Helium Temperaturen arbeitet. Dies bietet Vorteile weil sogar reaktive Oberflächen über eine Dauer von einigen Tagen sauber bleiben, was eine längere Experimentierphase zulässt. Zusätzlich zeigen diese Experimente bei tiefen Temperaturen weitere Vorteile wie kleine Driftwerte und tiefe Piezo Kriechraten. Der Ansatz bei diesem Tieftemperatur Rasterspitzen Mikroskop System ist die Implementierung eines fokussierenden Fabry Perot Interferometers das die folgenden Eigenschaften vorweist: - Der Betrieb bei kleinen Amplituden und mit steifen Cantilever setzt Sensoren mit einer hohen Ablenkempfindlichkeit voraus. Mit diesem fokussierenden Fabry Perot Interferometer (fFPi) kann eine Ablenkempfindlichkeit von 4fm/ sqrt(Hz) bei 1MHz erreicht werden. - Detektion mit einer grossen Bandbreite (DC-10MHz) erlauben einen Betrieb von Cantilever mit flexuralen und torsionalen Oszillation Modi. - Ein Laser mit einem Brennpunkt von 3µm lässt einen Betrieb mit einem ultra kleinen Cantilever zu, der 1/10 so gross ist wie ein konventioneller Cantilever. - Photothermische Anregung eines Cantilevers vermeidet unerwünschte mechanische Vibrationen rund um die Resonanzfrequenz. - Gleichzeitige flexural und torsional Kraftdetektion erlauben quantitative Untersuchungen von Reibungen und daher atomare Manipulationen mit Rasterkraft Mikroskopie (AFM). - Die Kombination und simultanen Betrieb von beiden Rasterspitzen Mikroskopen (AFM/STM) zeigen mehr Information als ein Raster Tunnel Mikroskop (STM) alleine. Eine Serie von Messungen mit Si(111)7x7, Herringbone Superstrukturen auf Au(111) und Highly Oriented Pyrolytic Graphite (HOPG) geben Information bezüglich der Leistungen des Systems preis. Einige dieser Leistungstests sind atomar aufgelöste Abbildungen bei drei unterschiedlichen Betriebstemperaturen im STM Betriebsart. Im nicht-Kontakt AFM (nc-AFM) Betriebsart, Abbildungen sind ausgeführt worden auf der Grundschwingung und der zweiten Oberschwingung. Zusätzliche Messungen wurden mit dem fFPi ausgeführt um den Einfluss der Laserkühlung auf den oszillierenden Cantilever bei drei unterschiedlichen Betriebstemperaturen zu quantifizieren. Das Ziel dieser Arbeit ist die Entwicklung, Implementation und Charakterisierung eines neuen Tieftemperatur Rasterspitzen Mikroskops mit einem ultra-empfindlichen und Breitband fokussierenden Fabry Perot Interferometer Ablenk Sensor, geeignet für den nicht-Kontakt AFM Betrieb mit kleinen, simultanen flexural und torsional Cantilever Schwingungsmodi. Naheliegende Erweiterungen des Systems gewährleisten einen simultan nc-AFM/STM Betrieb. Schlüsselwörter: Tieftemperatur simultan nc-AFM/STM aus Eigenbau, Spitzen-Probe Spalt Stabilität, PLL und Eigenanregungsbetrieb, Highly Oriented Pyrolytic Graphite (HOPG), reconstrukturiertes Si(111)7x7, Herringbone Superstruktur, fokussierenden Fabry Perot Interferometer, Cantilever Kühlung, Strahlendruck und photothermische Effekte

Efficient Generation of Coherent Stokes Field in Hydrogen Gas-Filled Hollow Core Photonic Crystal Fibres

In this paper, we study of the coherent Stokes generation in a transient Raman regime by Hydrogen gas-filled hollow-core photonic crystal fibres (HC-PCFs) configuration. The temporal and spatial evolution of the pump and Stokes field envelopes as well as the coherence and population inversion is numerically observed. The influence of the pump pulse width and gas pressure on the energy exchange along fiber and Stokes generation efficiency is investigated

Toward An IoT-based Expert System for Heart Disease Diagnosis

IoT technology has been recently adopted in the healthcare system to collect Electrocardiogram (ECG) signals for heart disease diagnosis and prediction. However, noises in collected ECG signals make the diagnosis and prediction system unreliable and imprecise. In this work, we have proposed a new lightweight approach to removing noises in collected ECG signals to perform precise diagnosis and prediction. First, we have used a revised Sequential Recursive (SR) algorithm to transform the signals into digital format. Then, the digital data is proceeded using a revised Discrete Wavelet Transform (DWT) algorithm to detect peaks in the data to remove noises. Finally, we extract some key features from the data to perform diagnosis and prediction based on a feature dataset. Redundant features are removed by using Fishers Linear Discriminant (FLD). We have used an ECG dataset from MIT-BIH (PhisioNet) to build a knowledge-base diagnosis features. We have implemented a proof-of concept system that collects and processes real ECG signals to perform heart disease diagnosis and prediction based on the built knowledge base

Multi-correlation between nematode communities and environmental variables in mangrove-shrimp ponds, Ca Mau Province, Southern Vietnam

Multi-correlation between bio-indices of nematode communities and ecological parameters in mangrove-shrimp farming ponds in Tam Giang commune, Nam Can District, Ca Mau Province, Vietnam were investigated. In which, diversities of nematode communities and several environmental variables in eight ponds were considered to process. Our findings underlined the high diversity of nematode communities in mangrove-shrimp farming ponds compared to other mangrove habitats. Nematode diversities provided more oppotunity in natural food for shrimp. Single correlation analyses showed that the species richness index correlated significantly to three variables (salinity, total organic carbon, and total nitrogen), the Margalef diversity index correlated to two variables (salinity, total organic carbon), and the expected number of species for 50 individuals index correlated with one variable (salinity). Results of multi-correlation analyses between the nematode bio-indices and the environmental variables were completely different from those of single-correlation analyses. In multi-correlation analyses, the species richness and the Margalef diversity index correlated to two variables (salinity, total organic carbon), Pielou’s evenness index and Hill indices correlated with dissolved oxygen, also the Hurlbert index correlated to total organic carbon. Hence, it is necessary to pay attention to the impact of complex interactions between the multi-environmental variables and nematode communities. This research aims to explain the differences between single- and multi-correlation for evaluation of the effects of environmental factors on nematodes as well as aquatic organisms.

An Analysis of Shoreline Changes Using Combined Multitemporal Remote Sensing and Digital Evaluation Model

Cua Dai estuary belonged to Quang Nam province is considered to be one of the localities of Vietnam having a complex erosion and accretion process. In this area, sandbars are recently observed with lots of arguments about the causes and regimes of formation. This could very likely result of not reliable source of information on shoreline evolution and a lack of historical monitoring data. Accurately identification of shoreline positions over a given period of time is a key to quantitatively and accurately assessing the beach erosion and accretion. The study is therefore to propose an innovative method of accurately shoreline positions for an analysis of coastal erosion and accretion in the Cua Dai estuary. The proposed technology of multitemporal remote sensing and digital evaluation model with tidal correction are used to analyse the changes in shoreline and estimate the rate of erosion and accretion. An empirical formula is, especially, exposed to fully interpret the shoreline evolution for multiple scales based on a limitation of satellite images during 1965 to 2018. The results show that there is a significant difference of shoreline shift between corrections and non-corrections of tidal. Erosion process tends to be recorded in the Cua Dai cape located in the Cua Dai ward, especially in the An Luong cape located in the Duy Hai commune with the length of 1050 m. Furthermore, it is observed that there is much stronger erosion in the north side compared with south side of Cua Dai estuary

BIODIVERSITY AND DISTRIBUTION PATTERNS OF FREE-LIVING NEMATODES COMMUNITIES IN BALAI RIVER, BENTRE PROVINCE

Nematodes communities in Ba Lai river, Ben Tre province were investigated in September of 2015 (eight stations from estuary to upstream). The results showed that the nematodes communities have characterized by high density and biodiversity, providing useful information of nematodes assemblages in freshwater habitas, in particular inland river. Also the results indicated that the distribution of nematodes communities in Ba Lai river was strongly discriminated between in and outside of dam with two groups. The Ba Lai dam may be reasons for cause  the nematodes distribution discontinuity. Present study is a pioneering attempt to record the impact of the dam on benthic-invertebrate in Vietnam

The effect of a dam construction on subtidal nematode communities in the Ba Lai Estuary, Vietnam

Nematode communities and relevant environmental variables were investigated to assess how the presence of a dam affects the Ba Lai estuary benthic ecosystem, in comparison to the adjacent dam-free estuary Ham Luong. Both estuaries are part of the Mekong delta system in Vietnam. This study has shown that the dam's construction had an effect on the biochemical components of the Ba Lai estuary, as observed by the local increase in total suspended solids and heavy metal concentrations (Hg and Pb) and by a significant oxygen depletion compared to the natural river of Ham Luong. The nematode communities were also different between the two estuaries in terms of density, genus richness, Shannon-Wiener diversity, and dominant genera. The Ba Lai estuary exhibited lower nematode densities but a higher diversity, while the genus composition only slightly differed between estuaries. The results indicate that the present nematode communities may be well adapted to the natural organic load, to the heavy metal accumulation and to the oxygen stress in both estuaries, but the dam presence may potentially continue to drive the Ba Lai's ecosystem to its tipping point

Does sunlight drive seasonality of TB in Vietnam? A retrospective environmental ecological study of tuberculosis seasonality in Vietnam from 2010 to 2015.

BACKGROUND: Tuberculosis (TB) is a major global health burden, with an estimated quarter of the world's population being infected. The World Health Organization (WHO) launched the "End TB Strategy" in 2014 emphasising knowing the epidemic. WHO ranks Vietnam 12th in the world of high burden countries. TB spatial and temporal patterns have been observed globally with evidence of Vitamin D playing a role in seasonality. We explored the presence of temporal and spatial clustering of TB in Vietnam and their determinants to aid public health measures. METHODS: Data were collected by the National TB program of Vietnam from 2010 to 2015 and linked to the following datasets: socio-demographic characteristics; climatic variables; influenza-like-illness (ILI) incidence; geospatial data. The TB dataset was aggregated by province and quarter. Descriptive time series analyses using LOESS regression were completed per province to determine seasonality and trend. Harmonic regression was used to determine the amplitude of seasonality by province. A mixed-effect linear model was used with province and year as random effects and all other variables as fixed effects. RESULTS: There were 610,676 cases of TB notified between 2010 and 2015 in Vietnam. Heat maps of TB incidence per quarter per province showed substantial temporal and geospatial variation. Time series analysis demonstrated seasonality throughout the country, with peaks in spring/summer and troughs in autumn/winter. Incidence was consistently higher in the south, the three provinces with the highest incidence per 100,000 population were Tay Ninh, An Giang and Ho Chi Minh City. However, relative seasonal amplitude was more pronounced in the north. Mixed-effect linear model confirmed that TB incidence was associated with time and latitude. Of the demographic, socio-economic and health related variables, population density, percentage of those under 15 years of age, and HIV infection prevalence per province were associated with TB incidence. Of the climate variables, absolute humidity, average temperature and sunlight were associated with TB incidence. CONCLUSION: Preventative public health measures should be focused in the south of Viet Nam where incidence is highest. Vitamin D is unlikely to be a strong driver of seasonality but supplementation may play a role in a package of interventions

Heatwaves and dengue outbreaks in Hanoi, Vietnam: New evidence on early warning.

BACKGROUND: Many studies have shown associations between rising temperatures, El Niño events and dengue incidence, but the effect of sustained periods of extreme high temperatures (i.e., heatwaves) on dengue outbreaks has not yet been investigated. This study aimed to compare the short-term temperature-dengue associations during different dengue outbreak periods, estimate the dengue cases attributable to temperature, and ascertain if there was an association between heatwaves and dengue outbreaks in Hanoi, Vietnam. METHODOLOGY/PRINCIPAL FINDINGS: Dengue outbreaks were assigned to one of three categories (small, medium and large) based on the 50th, 75th, and 90th percentiles of distribution of weekly dengue cases during 2008-2016. Using a generalised linear regression model with a negative binomial link that controlled for temporal trends, temperature variation, rainfall and population size over time, we examined and compared associations between weekly average temperature and weekly dengue incidence for different outbreak categories. The same model using weeks with or without heatwaves as binary variables was applied to examine the potential effects of extreme heatwaves, defined as seven or more days with temperatures above the 95th percentile of daily temperature distribution during the study period. This study included 55,801 dengue cases, with an average of 119 (range: 0 to 1454) cases per week. The exposure-response relationship between temperature and dengue risk was non-linear and differed with dengue category. After considering the delayed effects of temperature (one week lag), we estimated that 4.6%, 11.6%, and 21.9% of incident cases during small, medium, and large outbreaks were attributable to temperature. We found evidence of an association between heatwaves and dengue outbreaks, with longer delayed effects on large outbreaks (around 14 weeks later) than small and medium outbreaks (4 to 9 weeks later). Compared with non-heatwave years, dengue outbreaks (i.e., small, moderate and large outbreaks combined) in heatwave years had higher weekly number of dengue cases (p<0.05). Findings were robust under different sensitivity analyses. CONCLUSIONS: The short-term association between temperature and dengue risk varied by the level of outbreaks and temperature seems more likely affect large outbreaks. Moreover, heatwaves may delay the timing and increase the magnitude of dengue outbreaks

Optical pulse Self-compressor combined the Nonlinear coupler with Backward Raman fiber amplifier

Based on the nonlinearity of the nonlinear optical coupler (NOC) and the amplifying capacity of the backward Raman fiber amplifier (PBRFA), a new optical system to compress the optical pulse (optical pulse self-compressor: OPSC) is proposed. Using the expressions describing relationship between output intensities from both output ports and input one of NOC and the expression describing the amplification of the PBRFA, the compressing process of the optical pulse propagating through OPSC is simulated. The results show that the peak of optical pulse will be enhanced and the duration of optical pulse will be reduced significantly, and the shape of input pulse is completely compressed with certain efficiency. It means the optical pulse is self-compressed without the pump pulse