Optomechanical resonators based on low dimensional materials

Mechanical resonators based on low dimensional materials have attracted a lot of attention due to their remarkable properties. Their ultra-low mass and high Q factors make them exceptional sensors, offering new possibilities in the studies of the material strength and the thermodynamic properties of low dimensional materials. The goal of this thesis is to shed light on the thermal and elastic properties of low dimensional materials across a wide temperature range. The first part of the thesis is focused on the study of the temperature dependence of the stiffness of carbon nanotubes. By measuring the resonance frequency of singly clamped carbon nanotube resonators as a function of temperature, we can obtain information on the Young’s modulus of the measured carbon nanotubes. We observe a relative shift of the Young’s modulus over a large temperature range with a slope of -(173 +/- 65) ppm/K, consistent with two different theoretical models based on the thermal dynamics of the lattice. The results show the dependence of the fundamental mechanical mode on the phonons in carbon nanotubes via the Young’s modulus. The measured data also indicates the coupling between mechanical modes and the phonon thermal bath in nanotubes. The phonon thermal bath in our experiments likely operates in the Akhiezer limit. In the second part of the thesis, we present the temperature dependence of the thermal conductivity and the specific heat capacity in the MoSe2 monolayer in a larger temperature range. Both the thermal conductivity and the specific heat capacity measurements are consistent with predictions based on first-principles. The results show that the phonon transport in a MoSe2 monolayer can be both diffusive and ballistic, depending on the temperature of the monolayer. The method used in this measurement can be used to investigate the thermal properties of many two-dimensional materials. Furthermore, it opens the possibility to investigate interesting thermal transport regimes in two-dimensional materials like hydro-dynamic regime or anomalous heat conduction.Los resonadores mecánicos basados en materiales de baja dimensionalidad han llamado la atención de la comunidad científica debido a sus singulares propiedades. Su pequeña masa y sus altos factores de calidad (Q) los convierten en sensores excepcionales, ofreciendo un nuevo abanico de posibilidades en el estudio de las propiedades mecánicas y termodinamicas de los materiales de baja dimensionalidad. El objetivo de ésta tesis es el estudio de las propiedades térmicas y elásticas de los materiales de baja dimensionalidad en un amplio rango de temperaturas. La primera parte de la tesis se centra en la evolución de la rigidez de los nanotubo de carbono en función de la temperatura. La medida de la frecuencia de resonancia de un resonador basado en un nanotubos de carbono con un único punto de anclaje en función de la temperatura, ofrece información sobre el módulo de Young de dicho nanotubo. Observamos un cambio relativo del módulo de Young en un amplio rango de temperaturas con una pendiente de -(173 +/- 65) ppm/K, en acuerdo con dos modelos teóricos diferentes basados en la dinámica térmica de la red cristalina del material. Los resultados muestran la influencia de los fonones del nanotubo de carbono en el modo mecánico fundamental a través del módulo de Young. Los datos también indican el acoplamiento entre los modos mecánicos y el baño térmico de fonones en los nanotubos. Es probable que el baño térmico de fonones en nuestros experimentos opere en el límite de Akhiezer. En la segunda parte de la tesis, presentamos la evolución de la conductividad térmica y la capacidad calorífica específica de una monocapa MoSe2 en función de la temperatura para un rango más amplio. Tanto la conductividad térmica como las medidas de la capacidad calorífica específica concuerdan con las predicciones basadas en los primeros principios. Los resultados muestran que el transporte de fonones en la monocapa MoSe2 puede ser difusivo o balístico, dependiendo de la temperatura de dicha monocapa. El método utilizado en esta medida se puede utilizar para investigar las propiedades térmicas de muchos materiales bidimensionales. Asimismo, abre la posibilidad de investigar distintos regímenes de transporte térmico en materiales bidimensionales cómo el régimen hidrodinámico o la conducción de calor anómala.Postprint (published version

Optomechanical measurement of thermal transport in two-dimensional MoSe2 lattices

Nanomechanical resonators have emerged as sensors with exceptional sensitivities. These sensing capabilities open new possibilities in the studies of the thermodynamic properties in condensed matter. Here, we use mechanical sensing as a novel approach to measure the thermal properties of low-dimensional materials. We measure the temperature dependence of both the thermal conductivity and the specific heat capacity of a transition metal dichalcogenide (TMD) monolayer down to cryogenic temperature, something that has not been achieved thus far with a single nanoscale object. These measurements show how heat is transported by phonons in two-dimensional systems. Both the thermal conductivity and the specific heat capacity measurements are consistent with predictions based on first-principles

Evaluacija efekata različitih rezima ishrane na inflamatorni odgovor kod mladih fudbalera

Considering the limited knowledge regarding the effects of n-3 and n-6 PUFAs on the inflammatory response during physical activity, we aimed to evaluate the level of pro- and anti-inflammatory cytokines in young soccer players before and after a maximal physical load test at the beginning and end of a two-month training process. The study included 75 young footballers from Football School 'Kragujevac,' who were followed during the two-month training programme. The subjects were divided into the following groups: 1) control group (consumed a standard diet); 2) group that consumed fish oil (2500 mg of n-3 PUFAs per day); 3) group that consumed nutritional sunflower oil (2500 mg of n-6 PUFAs daily). The maximal progressive exercise test was performed using a treadmill belt. Venous blood samples were drawn 4 times for the determination of cytokine levels (IL-6 and TNF-α): before and after the exercise load test before the two-month training programme (initial measurement) and immediately before and after the exercise load test after the two-month training programme (control measurement). Supplementation with fish oil (n-3) has been associated with reduced levels of IL-6 compared with the initial values. After an acute bout of exercise, n-3 PUFAs did not show a significant effect on inflammatory marker dynamics, whereas n-6 PUFAs slightly stimulated the production of TNF-α.S'obzirom na ograničeno znanje o efektima polinezasićenih masnih kiselina (n-3 i n-6 PUFA-Polyunsaturated Fatty Acids), cilj ovog istraživanja bio je da se procene vrednosti pro- i antiinflamatornih medijatora u miru i nakon maksimalnog testa opterećenja pre i nakon dvomesečnog trenažnog programa. U studiji je učestvovalo 75 mladih fudbalera omladinske fudbalske škole 'Kragujevac', starosti od 18 - 19 godina, koji su bili praćeni tokom dva meseca. Oni su bili podeljeni u tri grupe: 1. kontrolna grupa (standardna ishrana), 2. grupa koja je konzumirala riblje ulje (2500mg n-3 PUFA dnevno), 3. grupa koja je konzumirala suncokretovo ulje (2500mg n-6 PUFA dnevno). Venski uzorci krvi za određivanje nivoa citokina (IL-6, TNF- α) uzimani su 4 puta: u miru i nakon testa opterećenja, pre i posle dvomesečnog trenažnog programa. Svakodnevna suplementacija ribljim uljem povezana je sa smanjenim vrednostima IL-6 u odnosu na njegove početne vrednosti. Upotreba različitih vrsta polinezasiđenih masnih kiselina nije bitnije uticala na proizvodnju citokina, neposredno nakon akutnog nastupa sportske aktivnosti (testa opterećenja)

Mass Sensing for the Advanced Fabrication of Nanomechanical Resonators

We report on a nanomechanical engineering method to monitor matter growth in real time via e-beam electromechanical coupling. This method relies on the exceptional mass sensing capabilities of nanomechanical resonators. Focused electron beam-induced deposition (FEBID) is employed to selectively grow platinum particles at the free end of singly clamped nanotube cantilevers. The electron beam has two functions: it allows both to grow material on the nanotube and to track in real time the deposited mass by probing the noise-driven mechanical resonance of the nanotube. On the one hand, this detection method is highly effective as it can resolve mass deposition with a resolution in the zeptogram range; on the other hand, this method is simple to use and readily available to a wide range of potential users because it can be operated in existing commercial FEBID systems without making any modification. The presented method allows one to engineer hybrid nanomechanical resonators with precisely tailored functionalities. It also appears as a new tool for studying the growth dynamics of ultrathin nanostructures, opening new opportunities for investigating so far out-of-reach physics of FEBID and related methods

Dietary assessment methods used for low-income populations in food consumption surveys: a literature review

In order to assess nutritional adequacy, reliable estimates of nutrient intake are required. Specifically, the EURopean micronutrient RECommendations Aligned (EURRECA) Network of Excellence needs clear guidelines oil methods suitable for assessing micronutrient intakes among vulnerable population groups. The objective of this project was to collect, evaluate data and review the suitability of methods used to assess dietary intake of low-income groups across Europe. A comprehensive literature review methodology was employed, which involved structured search MEDLINE, from 1990 to 2008, oil (nutrient intake methods) and (validity terms) and (human Studies) and finally (low-income terms). In addition, manual searches were conducted for published books and national studies. Seven Studies satisfied the selection criteria for inclusion in the review in which four dietary intake methods had been described and validated. Three other studies found in (lie grey literature used similar methods. Only one Study tested a variety of methods to assess reliability and the method preferred by those having low incomes. Preferred methods were 24 h recalls and a FFQ which, compared with the weighed inventory, also yielded higher estimates of energy and nutrient intakes. Many of the methods used in low-income populations have not been subjected to evaluation and consequently may not demonstrate sensitivity and/or Specificity When used in this population. Based oil One Study only, four multiple-pass 24 h recalls are recommended as the most appropriate method for the evaluation of nutritional adequacy in low-income households

Trypacidin, a Spore-Borne Toxin from Aspergillus fumigatus, Is Cytotoxic to Lung Cells

Inhalation of Aspergillus fumigatus conidia can cause severe aspergillosis in immunosuppressed people. A. fumigatus produces a large number of secondary metabolites, some of which are airborne by conidia and whose toxicity to the respiratory tract has not been investigated. We found that spores of A. fumigatus contain five main compounds, tryptoquivaline F, fumiquinazoline C, questin, monomethylsulochrin and trypacidin. Fractionation of culture extracts using RP-HPLC and LC-MS showed that samples containing questin, monomethylsulochrin and trypacidin were toxic to the human A549 lung cell line. These compounds were purified and their structure verified using NMR in order to compare their toxicity against A549 cells. Trypacidin was the most toxic, decreasing cell viability and triggering cell lysis, both effects occurring at an IC50 close to 7 µM. Trypacidin toxicity was also observed in the same concentration range on human bronchial epithelial cells. In the first hour of exposure, trypacidin initiates the intracellular formation of nitric oxide (NO) and hydrogen peroxide (H2O2). This oxidative stress triggers necrotic cell death in the following 24 h. The apoptosis pathway, moreover, was not involved in the cell death process as trypacidin did not induce apoptotic bodies or a decrease in mitochondrial membrane potential. This is the first time that the toxicity of trypacidin to lung cells has been reported

Difficulties experienced by consultants during lean design in the construction industry

Syfte: Syftet med denna rapport är att identifiera varför det är problematiskt för konsulter att arbeta med lean processer och ta reda på vad konsekvenserna av detta kan bli. Slutligen ska rapporten knyta ihop säcken och behandla frågan om hur det går att gå tillväga för att effektivare involvera konsulter i sitt arbete med lean och få det effektiva flöde som lean i grunden strävar efter. Metod: Metoden som har använts för att få fram resultat i denna studie är litteraturstudier samt semistrukturerade intervjuer av olika konsulter och uppdragsgivare. Resultat: Arbetets resultat har landat i att det är viktigt med en bra projektledning som trycker för att lean ska eftersträvas och följas, visuell styrning ska användas som hjälpmedel och för kortare avstämningar och den personliga kontakten mellan de involverade i projektet är avgörande. Allt detta ska varvas med en god mötesstruktur för att ständigt hålla alla uppdaterade. Konsekvenser: Att konsulter inte följer sagda lean processor vid beställning av entreprenör, leder till att konsulten arbetar på sitt eget sätt och kan således resultera i problem i senare skede mellan andra konsulter och/eller entreprenören. Fler organisationer väljer att arbeta efter ett lean-tänk och implementeringen av detta hade både förenklat och effektiviserat projekteringsskedet och samarbetet mellan entreprenörer och konsulter om det hade funnits mer underlag för hur arbetet kan förbättras. Begränsningar: Studien är begränsad till AF Bygg Göteborg, som själva anställer sina konsulter. Den är avgränsad till relationen mellan uppdragsgivare och konsulter samt konsulter sinsemellan. Studien kommer inte att studera effekterna av lean för företaget. Studien kommer heller inte att gå in på allmänna bestämmelser eller olika upphandlingsformer. Nyckelord: Lean, konsult, lean construction, the Toyota Way, Jidoka, konsulter och projektledning.Purpose: The aim of this report is to identify why consultants find it difficult to work with lean based projects and to find out the consequences of not following this philosophy. This report will discuss how it would be possible to more effectively involve consultants in their work with lean and maintain the effective flow that the lean philosophy strives for. Method: The methods used to achieve the results needed for this study are articles, books, scientific articles and semi-structured interviews with different consultants and taskmasters. Findings: The results of the study have shown that it is important to have a strong project management which really pushes for lean to be maintained and pursued. Visual steering is also something that should be pursued in order for consultants to more easily manage the lean idea. Some results have also shown that the personal connection between people working together in a project is of importance in order to maintain good communication. Finally, a good meeting structure, is maybe the most important part to make a lean philosophy work. Implications: The fact that consultants do not follow the said lean processor when ordering the contractor leads to the consultant working in their own way and can thus result in problems at a later stage between other consultants and / or the contractor. More organizations choose to work according to a lean and the implementation of this had both simplified and streamlined the design phase and the collaboration between contractors and consultants if there had been more basis for how the work could be improved. Limitations: The study is limited to AF Bygg Göteborg who themselves have hired all the consultants that the interviews were conducted with. It is also limited to the relation between the taskmasters and the consultants but also the consultants among themselves. The study will not study the effects of lean for this specific company. It will also not touch on general regulations nor different forms of procurements. Keywords: Lean, consultant, lean construction, the Toyota Way, Jidoka, consultants and project managment