Non-uniform spin wave softening in 2D magnonic crystals as a tool for opening omnidirectional magnonic band gaps

By means of the plane wave method we study spin wave dynamics in two-dimensional bi-component magnonic crystals based on a squeezed hexagonal lattice and consist of a permalloy thin film with cobalt inclusions. We explore the dependence of a spin wave frequency on the external magnetic field, especially in weak fields where the mode softening takes place. For considered structures, the mode softening proves to be highly non-uniform on both the mode number and the wave vector. We found this effect to be responsible for the omnidirectional band gap opening. Moreover, we show that the enhancement of the demagnetizing field caused by the squeezing of the structure is of crucial importance for the non-uniform mode softening. This allows us to employ this mechanism to design magnonic gaps with different sensitivity for the tiny change of the external field. The effects we have found should be useful in designing and optimization of spin wave filters highly tunable by a small external magnetic field.Comment: Final versio

Angular Dependent Magnetization Dynamics of Kagome Artificial Spin Ice Incorporating Topological Defects

We report angular-dependent spin-wave spectroscopy on kagome artificial spin ice made of large arrays of interconnected Ni80Fe20 nanobars. Spectra taken in saturated and disordered states exhibit a series of resonances with characteristic in-plane angular dependencies. Micromagnetic simulations allow us to interpret characteristic resonances of a two-step magnetization reversal of the nanomagnets. The dynamic properties are consistent with topological defects that are provoked via a magnetic field applied at specific angles. Simulations that we performed on previously investigated kagome artificial spin ice consisting of isolated nanobars show characteristic discrepancies in the spin wave modes which we explain by the absence of vertices.Comment: 14 pages and 5 figure

The population increase of the Hooded Crow, Corvus corone cornix Linnaeus, 1758, in Zagreb, from 2004 to 2017

Siva vrana (Corvus corone cornix, L.) eurazijska je vrsta ptica iz reda vrapčarki (Passeriformes), porodice vrana (Corvidae) koja nastanjuje veći dio europskog kontinenta, pretežno istočnu i sjevernu Europu. Oportunisti su koji uspješno iskorištavaju promjene uslijed urbanizacije krajolika, što pokazuje i rast njihovih populacija u raznim europskim gradovima. Cilj istraživanja bio kvantificirati istražiti brojnost i porast populacije sivih vrana na području Zagreba prebrojavanjem gnijezdećih parova unutar 16 odabranih kvadrata površine 1 km². Dobiveni podaci uspoređeni su s onima prikupljenim između 2004. i 2007. godine, te je utvrđen rast u gotovo svim odabranim kvadratima. Dokazana je korelacija između porasta sivih vrana i visokourbaniziranih područja grada ali i njihovo preferiranje parkova i ostalih otvorenih površina.The Hooded Crow (Corvus corone cornix, L.) is a Eurasian bird species which belongs to the order Passeriformes and family Corvidae. It is found across the European continent, mostly in Eastern and Northern Europe. They are opportunistic species that successfully exploit the habitat changes brought by urbanization, which is reflectedseen by the growth of their populations across European towns. The aim of this research was to quantify the increase of the Hooded Crow population in Zagreb by counting the nesting couples in 16 squares that have a surface of 1 km². The data was compared to those gathered between 2004 and 2007, and an increase has been shown in almost all of the squares. A correlation between the increase of the Hooded Crow population and the highly urbanized parts of the city was found, as well as their prefference has not been proven, as crows preferred parks and green areas

Optimization of Multi-Frequency Magnonic Waveguides with Enhanced Group Velocities by Exchange Coupled Ferrimagnet/Ferromagnet Bilayers

We report broadband spectroscopy and numerical analysis by which we explore propagating spin waves in a magnetic bilayer consisting of a 23 nm thick permalloy film deposited on 130 nm thick $Y_{3}Fe_{5}O_{12}$. In the bilayer, we observe a characteristic mode that exhibits a considerably larger group velocity at small in-plane magnetic field than both the magnetostatic and perpendicular standing spin waves. Using the finite element method, we confirm the observations by simulating the mode profiles and dispersion relations. They illustrate the hybridization of spin wave modes due to exchange coupling at the interface. The high-speed propagating mode found in the bilayer can be utilized to configure multi-frequency spin wave channels enhancing the performance of spin wave based logic devices

Brush-First Synthesis of Acid-Labile Star-Like Poly(ethylene glycol) Nanogels for Drug Delivery Applications

The development of multidrug-conjugated polymeric nanoparticles for drug delivery applications promises more effective forms of cancer therapy based on the target-specific, triggered release of therapeutic agents at the tumor site. Discrimination between healthy tissue and tumor cells can be achieved by exploiting the characteristics of the mildly acidic tumor microenvironment. While previous studies showed the potential of acid-responsive polymeric nanoparticles, low drug-loading and failure to release drugs in response to tumor-specific pH conditions remain a challenge in drug delivery and synthetic chemistry. This work presents the synthesis of acid-degradable star-like polymeric nanogels that allow high drug-loading and acid-triggered core degradation in tumor tissue based on the brush-first ring-opening metathesis polymerization (ROMP) method. These brush-arm star polymer (BASP) nanogels are composed of two monomers: (1) poly(ethylene glycol) (PEG) norbornene-terminated macromonomer providing biocompatible and water-soluble features and (2) the acid-cleavable acetal-based cross-linker enabling acid-triggered core degradation. After brush formation of PEG macromonomer resulting in the hydrophilic shell, a mixture of PEG macromonomer and cross-linker initiates the formation of the gel-like core via cross-linking. BASP nanogels were successfully synthesized using various ratios of cross-linker to PEG macromonomer. Characterization via gel permeation chromatography (GPC) confirmed the formation of mostly monomodal BASP nanogels with decreasing MW as the amount of PEG macromonomer is increased. Additional GPC analysis of acid degraded BASP nanogels suggests that the macromonomer increases the steric hindrance during cross-coupling and core formation resulting in smaller BASP nanogels. Furthermore, fluorescence studies show the successful loading of a fluorescein dye into BASP nanogel

There and Back Again: Exploring the Roles of Models and Natural History in Macroevolution

Ecological diversity in nature is tremendously complex. Evolutionary biologists and ecologists have sought to understand this complexity using foundational concepts like ecological niches, guilds, and adaptive zones. The merger of these concepts with stochastic models and phylogenies helped create the field of phylogenetic comparative methods, which has made fundamental contributions to our understanding of the evolutionary history of life’s rich ecological variety and the role ecology plays in the diversification of species and phenotypes and the assembly of species-rich communities. Despite this progress, however, phylogenetic comparative methods have been slow to expand their data repertoire. There is a general rarity of comparative datasets that include primary natural history observations of organisms in nature and of comparative methods to work with such data. The main contribution of this dissertation is to address this shortfall. I do so in three main ways. First, in earlier chapters I study some simple stochastic models of ecological character state change, revealing unappreciated subtleties that complicate our ability to interpret their results in terms of historical events. Second, building off lessons learned from these early chapters, I develop a new method that uses primary natural history observations to jointly infer the phylogenetic distribution of ecological niche states for individual species and their unsampled ancestors. Third, to demonstrate the flexibility of the new method, I conduct an empirical analysis on the diversification of snake feeding habits using a new comprehensive database of observations of prey acquisition by snakes that I compiled. Taken together, the research in this dissertation demonstrates how fundamental observations of organisms in nature can be used to make quantitative inferences about the macroevolution of complex ecological traits and suggests new ways of integrating natural history data into comparative biology.PHDEcology and Evolutionary BiologyUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/163161/1/mgru_1.pd

Optimization of the extraordinary magnetoresistance in semiconductor-metal hybrid structures for magnetic-field sensor applications

Semiconductor-metal hybrid structures can exhibit a very large geometrical magnetoresistance effect, the so-called extraordinary magnetoresistance (EMR) effect. In this paper, we analyze this effect by means of a model based on the finite element method and compare our results with experimental data. In particular, we investigate the important effect of the contact resistance $\rho_c$ between the semiconductor and the metal on the EMR effect. Introducing a realistic $\rho_c=3.5\times 10^{-7} \Omega{\rm cm}^2$ in our model we find that at room temperature this reduces the EMR by 30% if compared to an analysis where $\rho_c$ is not considered.Comment: 4 pages; manuscript for MSS11 conference 2003, Nara, Japa