New particle formation (NPF) is the source of over half of the atmosphere's cloud condensation nuclei, thus influencing cloud properties and Earth's energy balance. Unlike in the planetary boundary ...layer, few observations of NPF in the free troposphere exist. We provide observational evidence that at high altitudes, NPF occurs mainly through condensation of highly oxygenated molecules (HOMs), in addition to taking place through sulfuric acid–ammonia nucleation. Neutral nucleation is more than 10 times faster than ion-induced nucleation, and growth rates are size-dependent. NPF is restricted to a time window of 1 to 2 days after contact of the air masses with the planetary boundary layer; this is related to the time needed for oxidation of organic compounds to form HOMs. These findings require improved NPF parameterization in atmospheric models.
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The skin offers an attractive way for dermal and transdermal drug delivery that is why the drug still needs certain qualities to transcend the outermost layer of the skin, the stratum ...corneum. The requirements are: drugs with a maximum molecular weight of 1kDa, high lipophilicity and a certain polarity. This would restrict the use of a transdermal delivery of macromolecules, which would make the drug more effective in therapeutic administration.
Various studies have shown that macromolecules without support do not penetrate the human skin.
This effect can be achieved using physical and chemical methods, as well as biological peptides.
The most popular physical method is the use of microneedles to create micropores in the skin and release the active agent in different sections. But also, other methods have been tested. Microjets, lasers, electroporation, sonophoresis and iontophoresis are also promising methods to successfully deliver dermal and transdermal macromolecules. Additionally, there are different penetration enhancer groups and biological peptides, which are also considered to be interesting approaches of enabling macromolecules to travel along the skin.
All these methods will be described and evaluated in this review article.
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•Synthesis of a set of block copolymers with oleophobic-hydrophilic properties.•Preparation of polymer brushes with switchable wettability by grafting-to.•Adjustment of switching ...amplitude by the ratio of the block lengths to each other.•Analysis of different switching behaviors by molecular dynamic simulations.•The prepared polymer brush films have easy-to-clean properties.
The combination of different wetting states, such as hydrophilic and oleophobic, in an adaptive polymer layer provides new opportunities in the field of easy-to-clean and anti-fog coatings. In this work, the synthesis of new end-functionalized well-defined block copolymers consisting of a hydrophilic poly(acrylic acid) (PAA) block and an oleophobic poly(1,1,1,3,3,3-hexafluoroisopropyl methacrylate) (PHFIPMA) block of different block length was investigated. This was achieved by parallel synthesis of the single blocks separately using atom transfer radical polymerization (ATRP), and subsequent block coupling by copper(I)-catalyzed click chemistry. A hydroxy end-group functionalization allowed these polymers to be assembled into dense polymer brushes via a grafting-to approach. The architecture of theses brushes and the orientation of the chains within the films were studied using angle-resolved X-ray photoelectron spectroscopy (ARXPS). To study the influence of the lengths and ratio of the two blocks on the switching of the wettability, contact angle measurements were performed demonstrating the correlation between structure and functionality. It was found that an increasing length of the hydrophilic block, while keeping the length of the oleophobic block constant, leads to an increase of the switching amplitude. Molecular Dynamic Simulations, which gave deeper insights into changes of the brush architecture during switching, enabled in combination with chemical analysis at the nanometer scale (ARXPS) conclusions about the influence of molecular rearrangements inside the brush on macroscopic changes at the outer surface of the brush due to external stimuli. Finally, oil spray-off experiments demonstrated the potential of these new adaptive polymer brushes as easy-to-clean coatings.
Because of its multiresponsive behavior upon variation of pH value, temperature, and ionic strength, poly(N,N-dimethylaminoethyl methacrylate) (PDMAEMA) is an attractive candidate for adaptive ...surface coatings, especially in the field of biomedical sensors. In the presented article, PDMAEMA Guiselin brushes (5–12 nm, dry thickness) were prepared by the grafting-to approach, and the thermoresponsive UCST-type (upper critical solution temperature) behavior of the generated films, induced by Fe(CN)63–, was demonstrated for the first time. To clarify the specific mechanism of the temperature responsiveness, the molecular interactions between polymer chains and complex ions were studied by in situ infrared spectroscopy and in situ ellipsometry, showing wavenumber shifts of the ν(CN) band due to ion pairing as well as changes of the ν(OH) band intensity due to swelling. Conclusively, experimental data suggest that the electrostatic interaction between the two components plays a significant role in the thermoresponsive behavior of PDMAEMA films. Using this knowledge, the UCST of the PDMAEMA Guiselin brushes could be adjusted between 34.0 ± 1.2 °C at pH 8 and 40.7 ± 2.0 °C at pH 5.
Poly(N,N-dimethylaminoethyl methacrylate) (PDMAEMA) is an attractive polymer for switchable surface coatings based on its multiresponsiveness toward environmental triggers (temperature, pH-value, ...ionic strength). In this in situ study, we present the complex and tunable thermoresponsiveness of PDMAEMA Guiselin brushes (9 nm, dry thickness), which were prepared via an efficient grafting-to approach. Combining in situ atomic force microscopy (AFM) visualizing the surface topography (x–y plane) and spectroscopic ellipsometry monitoring the swelling behavior of the polymer film (layer thickness, z-direction) offers for the first time a three-dimensional insight into thermoresponsive transitions on the nanoscale. While PDMAEMA films exhibit LCST behavior in the presence of monovalent counterions, it can easily be switched toward an UCST thermoresponsiveness via the addition of small quantities of multivalent ions. In both cases, the transition temperature as well as the sharpness and reversibility of the transition can be tuned via a second external trigger, the ionic strength. Whereas homogeneous surfaces were observed both below and above the LCST in monovalent salt solutions, the UCST transition was characterized by the in situ formation of a nanostructured surface of pinned PDMAEMA micelles with entrapped multivalent counterions. Moreover, it was demonstrated for the first time that the characteristic dimensions of the nanopattern (the diameter and height of the pinned micelles) could be tuned in situ by the pH- and induced UCST thermoresponsiveness of PDMAEMA. This approach therefore provides a novel bottom-up strategy to create and control polymeric nanostructures in an aqueous environment.
Stereotactic body radiotherapy (SBRT) applies high doses and requires advanced techniques to spare surrounding tissue in the presence of organ motion. In this work patient individual phase gating is ...investigated. We studied peripheral and central primary lung tumors. The internal target volume (ITV) was defined including different numbers of phases picked from a 4D Computed tomography (CT) defining the gating window (gw). Planning target volume (PTV) reductions depending on the gw were analyzed. A treatment plan was calculated on a reference phase CT (rCT) and the dose for each breathing phase was calculated and accumulated on the rCT. We compared the dosimetric results with the dose calculated when all breathing phases were included for ITV definition. GWs including 1 to 10 breathing phases were analyzed. We found PTV reductions up to 38.4%. The mean reduction of the lung volume receiving 20 Gy due to gating was found to be 25.7% for peripheral tumors and 16.7% for central tumors. Gating considerably reduced esophageal doses. However, we found that simple reduction of the gw does not necessarily influence the dose in a clinically relevant range. Thus, we suggest a patient individual definition of the breathing phases included within the gw.
Abstract
The creation of novel approaches to reduce the icing of devices is of economic, technical, and ecological interest. Passive deicing approaches based on thin polymer layers show high ...potential. (Super)hydrophilic films, characterized by high swelling and surface energy, exhibit a self‐lubricating interfacial layer that can influence ice adhesion. For this purpose, a polymer layer consisting of zwitterionic 2‐methacryloyloxyethyl phosphorylcholine (MPC) and glycidyl methacrylate (GMA) is presented and investigated with respect to its icing behavior. The dependence of the swelling behavior of these layers on temperature and a stabilization of the swelling even at low temperatures is shown and can be directly influenced by the grafting conditions, which have a significant impact on the resulting ice thickness and deicing performance. In addition to the formation of a thinner ice layer, the polymer coatings grafted for 16 h are characterized by excellent deicing performance, resulting in consistently very low ice layer thicknesses in repeated icing–deicing cycles compared to the investigated reference SiO
2
. Due to these properties, the developed film has high application potential as a coating for heat exchangers, as it enables a reduction of the time between defrosting cycles and the distance between the plates, resulting in energy and material savings.
The Hamburg Aerosol Module version 2.3 (HAM2.3) from the ECHAM6.3‐HAM2.3 global atmosphere‐aerosol model is coupled to the recently developed icosahedral nonhydrostatic ICON‐A (icon‐aes‐1.3.00) ...global atmosphere model to yield the new ICON‐A‐HAM2.3 atmosphere‐aerosol model. The ICON‐A and ECHAM6.3 host models use different dynamical cores, parameterizations of vertical mixing due to sub‐grid scale turbulence, and parameter settings for radiation balance tuning. Here, we study the role of the different host models for simulated aerosol optical thickness (AOT) and evaluate impacts of using HAM2.3 and the ECHAM6‐HAM2.3 two‐moment cloud microphysics scheme on several meteorological variables. Sensitivity runs show that a positive AOT bias over the subtropical oceans is remedied in ICON‐A‐HAM2.3 because of a different default setting of a parameter in the moist convection parameterization of the host models. The global mean AOT is biased low compared to MODIS satellite instrument retrievals in ICON‐A‐HAM2.3 and ECHAM6.3‐HAM2.3, but the bias is larger in ICON‐A‐HAM2.3 because negative AOT biases over the Amazon, the African rain forest, and the northern Indian Ocean are no longer compensated by high biases over the sub‐tropical oceans. ICON‐A‐HAM2.3 shows a moderate improvement with respect to AOT observations at AERONET sites. A multivariable bias score combining biases of several meteorological variables into a single number is larger in ICON‐A‐HAM2.3 compared to standard ICON‐A and standard ECHAM6.3. In the tropics, this multivariable bias is of similar magnitude in ICON‐A‐HAM2.3 and in ECHAM6.3‐HAM2.3. In the extra‐tropics, a smaller multivariable bias is found for ICON‐A‐HAM2.3 than for ECHAM6.3‐HAM2.3.
Plain Language Summary
Aerosols are tiny particles in the air which are either emitted into the atmosphere directly or formed from precursor gases such as sulfur dioxide. Aerosols reflect and absorb solar radiation and affect the radiative properties of clouds. In order to estimate how changing emissions of aerosol precursor gases and aerosols affect the radiation budget of the atmosphere, aerosol models are coupled to global atmosphere models. Here, an aerosol model that has already been part of a well‐established coupled model is coupled to a recently developed atmosphere model. The reasons for differences between the original and the new model are investigated and simulated aerosol optical thickness is evaluated against observations. The aerosol optical thickness over subtropical oceans is lower in the new model, which is in better agreement with estimates from satellite observations. This better agreement is traced back to a parameter setting in the cloud description part in the new model. However, because cancellation of positive and negative biases is reduced in the new model, the global mean aerosol optical thickness is biased lower the new model. A bias score based on several meteorological variables is lower in the new model because of lower biases in the extra‐tropics.
Key Points
The new ICON‐A‐Hamburg Aerosol Module version 2.3 (HAM2.3) global atmosphere‐aerosol model is introduced
The sensitivity of simulated aerosol optical thickness (AOT) to using two different host models but the same aerosol module is investigated
A positive AOT bias over subtropical oceans is remedied in ICON‐A‐HAM2.3 because of a different parameter setting in the host model
Properties of GaN Nanowires Grown by Molecular Beam Epitaxy Geelhaar, L.; Chèze, C.; Jenichen, B. ...
IEEE journal of selected topics in quantum electronics,
2011-July-Aug., 2011-07-00, 20110701, Letnik:
17, Številka:
4
Journal Article
Recenzirano
On Si(1 1 1) and Si(0 0 1), GaN nanowires (NWs) form in a self-induced way without the need for any external material. On sapphire, NW growth is induced by Ni collectors. Both types of NWs exhibit ...the wurtzite crystal structure and grow in the Ga-polar C-direction perpendicular to the substrate. The NW sidewalls are M-plane facets, although on the Ni-induced NWs also A-plane segments form, if the growth temperature is low. Both self-induced and collector-induced NWs are free of strain and epitaxially aligned to the substrate, but in particular the former show a significant spread in tilt and twist caused by a mostly amorphous interfacial layer of Si-N. The self-induced NWs are virtually free of extended defects, but the collector-induced NWs contain many stacking faults. The photoluminescence of the former is significantly brighter and sharper. The spectra of single, dispersed, self-induced NWs contain extremely sharp excitonic lines. Significant emission is caused by excitons bound to donors close to the surface whose binding energy is reduced compared to the bulk value. In comparison, both the microstructure and optical properties of the self-induced NWs are superior. The limited material quality of the collector-induced NWs can be explained by detrimental effects of the collector.
To cover the microscopic tumor spread in squamous cell carcinoma of the esophagus (SCC), longitudinal margins of 3-4 cm are used for radiotherapy (RT) protocols. However, smaller margins of 2-3 cm ...might be reasonable when advanced diagnostic imaging is integrated into target volume delineation. Purpose of this study was to compare the dose distribution and deposition to the organs at risk (OAR) for different longitudinal margins using a DVH- and NTCP-based approach.
Ten patients with SCC of the middle or lower third were retrospectively selected. Three planning target volumes (PTV) with longitudinal margins of 4 cm, 3 cm and 2 cm and an axial margin of 1.5 cm to the gross target volume (GTV) were defined for each patient. For each PTV two treatment plans with total doses of 41.4 Gy (neoadjuvant treatment) and 50.4 Gy (definite treatment) were calculated. Dose to the lungs, heart, myelon and liver were then evaluated and compared between different PTVs.
When using a longitudinal margin of 3 cm instead of 4 cm, all dose parameters (Dmin, Dmean, Dmedian and V5-V35), except Dmax could be significantly reduced for the lungs. Regarding the heart, a significant reduction was seen for Dmean and V5, but not for Dmin, Dmax, Dmedian and V10-V35. When comparing a longitudinal margin of 4 cm to a longitudinal margin of 2 cm, a significant difference was calculated for Dmin, Dmean, Dmedian and V5-V35 of the lungs and for Dmax, Dmean and V5-V35 of the heart. Nevertheless, no difference was seen for median heart dose. An additional dose reduction for V10 of the heart was achieved for definite treatment plans when using a longitudinal margin of 3 cm. The NTCP-based risk of pneumonitis was significantly reduced by a margin reduction to 2 cm for neoadjuvant and definite treatment plans.
Reduction of longitudinal margins from 4 cm to 3 cm can significantly reduce the dose to lungs and Dmean of the heart. Despite clinical benefit and oncologic outcome remain unclear, reduction of the longitudinal margins might provide the opportunity to reduce side effects of chemoradiation (CRT) for SCC in upcoming studies.
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