33 research outputs found
Der Einfluss des mikrosozialen und makroökonomischen Umfelds sowie dem Standort auf den Erfolg von Oberwalliser Beherbergungen
Im Rahmen meiner Bachelorarbeit befasse ich mich mit der Analyse von Oberwalliser Be- herbergungsbetrieben
Recommended from our members
Energetic particle influence on the Earth's atmosphere
This manuscript gives an up-to-date and comprehensive overview of the effects of energetic particle precipitation (EPP) onto the whole atmosphere, from the lower thermosphere/mesosphere through the stratosphere and troposphere, to the surface. The paper summarizes the different sources and energies of particles, principally
galactic cosmic rays (GCRs), solar energetic particles (SEPs) and energetic electron precipitation (EEP). All the proposed mechanisms by which EPP can affect the atmosphere
are discussed, including chemical changes in the upper atmosphere and lower thermosphere, chemistry-dynamics feedbacks, the global electric circuit and cloud formation. The role of energetic particles in Earth’s atmosphere is a multi-disciplinary problem that requires expertise from a range of scientific backgrounds. To assist with this synergy, summary tables are provided, which are intended to evaluate the level of current knowledge of the effects of energetic particles on processes in the entire atmosphere
Recommended from our members
Research and Design of a Routing Protocol in Large-Scale Wireless Sensor Networks
无线传感器网络,作为全球未来十大技术之一,集成了传感器技术、嵌入式计算技术、分布式信息处理和自组织网技术,可实时感知、采集、处理、传输网络分布区域内的各种信息数据,在军事国防、生物医疗、环境监测、抢险救灾、防恐反恐、危险区域远程控制等领域具有十分广阔的应用前景。 本文研究分析了无线传感器网络的已有路由协议,并针对大规模的无线传感器网络设计了一种树状路由协议,它根据节点地址信息来形成路由,从而简化了复杂繁冗的路由表查找和维护,节省了不必要的开销,提高了路由效率,实现了快速有效的数据传输。 为支持此路由协议本文提出了一种自适应动态地址分配算——ADAR(AdaptiveDynamicAddre...As one of the ten high technologies in the future, wireless sensor network, which is the integration of micro-sensors, embedded computing, modern network and Ad Hoc technologies, can apperceive, collect, process and transmit various information data within the region. It can be used in military defense, biomedical, environmental monitoring, disaster relief, counter-terrorism, remote control of haz...学位:工学硕士院系专业:信息科学与技术学院通信工程系_通信与信息系统学号:2332007115216
Synthesis of Cone-Shaped Colloids from Rod-Like Silica Colloids with a Gradient in the Etching Rate
We present the synthesis of monodisperse cone-shaped silica colloids and their fluorescent labeling. Rod-like silica colloids prepared by ammonia-catalyzed hydrolysis and condensation of tetraethyl orthosilicate in water droplets containing polyvinylpyrrolidone cross-linked by citrate ions in pentanol were found to transform into cone-shaped particles upon mild etching by NaOH in water. The diameter and length of the resulting particles were determined by those of the initial rod-like silica colloids. The mechanism responsible for the cone-shape involves silica etching taking place with a varying rate along the length of the particle. Our experiments thus also lead to new insights into the variation of the local particle structure and composition. These are found to vary gradually along the length of the rod, as a result of the way the rod grows out of a water droplet that keeps itself attached to the flat end of the bullet-shaped particles. Subtle differences in composition and structure could also be resolved by high-resolution stimulated emission depletion confocal microscopy on fluorescently labeled particles. The incorporation of a fluorescent dye chemically attached to an amine-based silane coupling agent resulted in a distribution of fluorophores mainly on the outside of the rod-shaped particles. In contrast, incorporation of the silane coupling agent alone resulted in a homogeneous distribution. Additionally, we show that etching rods, where a silane coupling agent alone was incorporated and subsequently coupled to a fluorescent dye, resulted in fluorescent silica cones, the orientation of which can be discerned using super-resolution confocal microscopy
Synthesis of Cone-Shaped Colloids from Rod-Like Silica Colloids with a Gradient in the Etching Rate
We present the synthesis of monodisperse cone-shaped silica colloids and their fluorescent labeling. Rod-like silica colloids prepared by ammonia-catalyzed hydrolysis and condensation of tetraethyl orthosilicate in water droplets containing polyvinylpyrrolidone cross-linked by citrate ions in pentanol were found to transform into cone-shaped particles upon mild etching by NaOH in water. The diameter and length of the resulting particles were determined by those of the initial rod-like silica colloids. The mechanism responsible for the cone-shape involves silica etching taking place with a varying rate along the length of the particle. Our experiments thus also lead to new insights into the variation of the local particle structure and composition. These are found to vary gradually along the length of the rod, as a result of the way the rod grows out of a water droplet that keeps itself attached to the flat end of the bullet-shaped particles. Subtle differences in composition and structure could also be resolved by high-resolution stimulated emission depletion confocal microscopy on fluorescently labeled particles. The incorporation of a fluorescent dye chemically attached to an amine-based silane coupling agent resulted in a distribution of fluorophores mainly on the outside of the rod-shaped particles. In contrast, incorporation of the silane coupling agent alone resulted in a homogeneous distribution. Additionally, we show that etching rods, where a silane coupling agent alone was incorporated and subsequently coupled to a fluorescent dye, resulted in fluorescent silica cones, the orientation of which can be discerned using super-resolution confocal microscopy
Sculpting Silica Colloids by Etching Particles with Nonuniform Compositions
We present the synthesis of new shapes
of colloidal silica particles
by manipulating their chemical composition and subsequent etching.
Segments of silica rods, prepared by the ammonia catalyzed hydrolysis
and condensation of tetraethylorthosilicate (TEOS) from polyvinylpyrrolidone
loaded water droplets, were grown under different conditions. Upon
decreasing temperature, delaying ethanol addition, or increasing monomer
concentration, the rate of dissolution of the silica segment subsequently
formed decreased. A watery solution of NaOH (∼mM) selectively
etched these segments. Further tuning the conditions resulted in rod–cone
or cone–cone shapes. Deliberately modulating the composition
along the particle’s length by delayed addition of (3-aminopropyl)-triethoxysilane
(APTES) also allowed us to change the composition stepwise. The faster
etching of this coupling agent in neutral conditions or HF afforded
an even larger variety of particle morphologies while in addition
changing the chemical functionality. A comparable step in composition
was applied to silica spheres. Biamine functional groups used in a
similar way as APTES caused a charge inversion during the growth,
causing dumbbells and higher order aggregates to form. These particles
etched more slowly at the neck, resulting in a biconcave silica ring
sandwiched between two silica spheres, which could be separated by
specifically etching the functionalized layer using HF
Homogenous overexpression of the extracellular matrix protein Netrin-1 in a hollow fiber bioreactor
The production of recombinant proteins for functional and biophysical studies, especially in the field of structural determination, still represents a challenge as high quality and quantities are needed to adequately perform experiments. This is in part solved by optimizing protein constructs and expression conditions to maximize the yields in regular flask expression systems. Still, work flow and effort can be substantial with no guarantee to obtain improvements. This study presents a combination of workflows that can be used to dramatically increase protein production and improve processing results, specifically for the extracellular matrix protein Netrin-1. This proteoglycan is an axon guidance cue which interacts with various receptors to initiate downstream signaling cascades affecting cell differentiation, proliferation, metabolism, and survival. We were able to produce large glycoprotein quantities in mammalian cells, which were engineered for protein overexpression and secretion into the media using the controlled environment provided by a hollow fiber bioreactor. Close monitoring of the internal bioreactor conditions allowed for stable production over an extended period of time. In addition to this, Netrin-1 concentrations were monitored in expression media through biolayer interferometry which allowed us to increase Netrin-1 media concentrations tenfold over our current flask systems while preserving excellent protein quality and in solution behavior. Our particular combination of genetic engineering, cell culture system, protein purification, and biophysical characterization permitted us to establish an efficient and continuous production of high-quality protein suitable for structural biology studies that can be translated to various biological systems
Regiospecific Nucleation and Growth of Silane Coupling Agent Droplets onto Colloidal Particles
Nucleation-and-growth
processes are used extensively in the synthesis
of spherical colloids, and more recently regiospecific nucleation-and-growth
processes have been exploited to prepare more complex colloids such
as patchy particles. We demonstrate that surface geometry alone can
be made to play the dominant role in determining the final particle
geometry in such syntheses, meaning that intricate chemical surface
patternings are not required. We present a synthesis method for “lollipop”-shaped
colloidal heterodimers (patchy particles), combining a recently published
nucleation-and-growth technique with our recent findings that particle
geometry influences the locus of droplet adsorption onto anisotropic
template particles. Specifically, 3-methacryloxypropyl trimethoxysilane
(MPTMS) is nucleated and grown onto bullet-shaped and nail-shaped
colloids. The shape of the template particle can be chosen such that
the MPTMS adsorbs regiospecifically onto the flat ends. In particular,
we find that particles with a wider base increase the range of droplet
volumes for which the minimum in the free energy of adsorption is
located at the flat end of the particle compared with bullet-shaped
particles of the same aspect ratio. We put forward an extensive analysis
of the synthesis mechanism and experimentally determine the physical
properties of the heterodimers, supported by theoretical simulations.
Here we numerically optimize, for the first time, the shape of finite-sized
droplets as a function of their position on the rod-like silica particle
surface. We expect that our findings will give an impulse to complex
particle creation by regiospecific nucleation and growth
Heparins mediate the multimer assembly of secreted Noggin
Extracellular matrix proteins are most often defined by their direct function that involves receptor binding and subsequent downstream signaling. However, these proteins often contain structural binding regions that allow for the proper localization in the extracellular space which guides its correct function in a local and temporal manner. The regions that serve a structural function, although often associated with disease, tend to have a limited understanding. An example of this is the extracellular matrix protein Noggin; as part of the bone morphogenetic protein inhibitor family, Noggin serves a crucial regulatory function in mammalian developmental stages and later periods of life. Noggin's regular function, after its expression and extracellular release, is mediated by its retention in close proximity to the cellular surface by glycosaminoglycans, specifically heparin and heparan sulfate. Using a biophysical hybrid method approach, we present a close examination of the Noggin heparin binding interface, study its dynamic binding behaviors and observe supramolecular Noggin assemblies mediated by heparin ligands. This confirms previously suggested models of non-covalent protein assemblies mediated through glycosaminoglycans that exist in the extracellular matrix. Further, structural analyses through molecular dynamics simulations allowed us to determine contribution energies for each protein residue involved in ligand binding and correlate this to disease associated mutation data. Our combination of various biophysical and computational methods that characterize the heparin binding interface on Noggin and its protein dynamics expands on the functional understanding of Noggin and can readily be applied to other protein systems