Ripple-to-dome transition: the growth evolution of Ge on vicinal Si(1 1 10) surface

We present a detailed scanning tunnelling microscopy study which describes the morphological transition from ripple to dome islands during the growth of Ge on the vicinal Si(1 1 10) surface . Our experimental results show that the shape evolution of Ge islands on this surface is markedly different from that on the flat Si(001) substrate and is accomplished by agglomeration and coalescence of several ripples. By combining first principle calculations with continuum elasticity theory, we provide an accurate explanation of our experimental observations

Producing an Online Undergraduate Literary Magazine: A Guide to Using Problem-Based Learning in the Writing and Publishing Classroom

This article will illustrate how a problem-based learning (PBL) course (Savery, 2006) can be used in a writing program as a vehicle for both creative and preprofessional learning. English 420: Writing, Publishing, and Editing is offered every fall, and its counterpart, English 423: Writing, Publishing, and Editing is offered each spring. The courses, positioned at the end of a sequenced series of prerequisite writing courses, provide a creative, applied writing experience that offers students professional practice through producing the digital version of Cabrini College’s literary magazine, Woodcrest. In the 2012–2013 school year, the English Department ran its first cycle of this model, which, at the time of this writing, is in its third year. Three successive Gold Medal ratings of our online literary magazine (2012–2013, 2013–2014, 2014–2015) by the Columbia Scholastic Press Association (CSPA) and a Gold Crown Award (2013–2014) suggest that problem-based learning, when used to cultivate an authentic online literary publication, familiarizes students with the life cycle of creative projects and enhances their writing. Writing students benefit from experiencing the interdisciplinary, collaborative, and student-driven work that problem-based learning prioritizes. This article will provide many resources to illustrate how PBL can be used when transitioning a literary magazine from print to online in a class-based setting

Hug-like island growth of Ge on strained vicinal Si(111) surfaces

We examine the structure and the evolution of Ge islands epitaxially grown on vicinal Si(111) surfaces by scanning tunneling microscopy. Contrary to what is observed on the singular surface, three-dimensional Ge nanoislands form directly through the elastic relaxation of step-edge protrusions during the unstable step-flow growth. As the substrate misorientation is increased, the islands undergo a shape transformation which is driven by surface energy minimization and controlled by the miscut angle. Using finite element simulations, we show that the dynamics of islanding observed in the experiment results from the anisotropy of the strain relaxation.Comment: 4 figure

Islanding, growth mode and ordering in Si heteroepitaxy on Ge(001) substrates structured by thermal annealing

Si/Ge heteroepitaxial dots under tensile strain are grown on nanostructured Ge substrates produced by high-temperature flash heating exploiting the spontaneous faceting of the Ge(001) surface close to the onset of surface melting. A very diverse growth mode is obtained depending on the specific atomic structure and step density of nearby surface domains with different vicinal crystallographic orientations. On highly-miscut areas of the Ge(001) substrate, the critical thickness for islanding is lowered to about 5 ML, in contrast to the 11 ML reported for the flat Ge(001) surface, while on unreconstructed (1x1) domains the growth is Volmer-Weber driven. An explanation is proposed considering the diverse relative contributions of step and surface energies on misoriented substrates. In addition, we show that the bottom-up pattern of the substrate naturally formed by thermal annealing determines a spatial correlation for the dot sites

Step-step interaction on vicinal Si(001) surfaces studied by scanning tunneling microscopy

We report on measurements of step-step interaction on a flat Si(111)−(7×7) surface and on vicinal Si(001) surfaces with miscut angles ranging between 0.2° and 8°. Starting from scanning tunneling microscopy images of these surfaces and describing steps profile and interactions by the continuum step model, we measured the self-correlation function of single steps and the distribution of terrace widths. Empirical parameters, such as step stiffness and step-step interaction strength, were evaluated from the images. The present experiment allows to assess the dependence of the step-step repulsion on miscut angle, showing how parameters drawn from tunneling images can be used to interpolate between continuum mesoscopic models and atomistic calculations of vicinal surfaces

Life-history and diet of two populations of Natrix maura (Reptilia, Colubridae) from contrasted habitats in Sardinia

Aspects of general ecology and population biology of two populations of freeliving viperine snakes (Natrix maura) were studied in Mediterranean localities of the island of Sardinia (Thyrrenian Sea, Italy). The apparent adult sex-ratio was not significantly different from equality, but males were slightly more numerous than females. The diet consisted mainly of arnphibians, both adults and tadpoles (area A) or fish (area B). Females were significantly longer than males. Reproduction was yearly, and clutch size and female total length were positively correlated. A hundred and seven live offsprings were obtained from 135 eggs (79.2% of successful incubation rates). The proportion of unsuccessful incubation was not significantly correlated with either female total length or clutch size. There was no evidence of a trade-off between clutch size and offspring size, as hatchlings were no smaller in clutches that were unusually large in relation to maternal body size. Oviposition date was correlated with neither maternal length nor clutch size. lncubation period was significantly correlated with mean hatchling size, but not with either clutch size or maternal length. No female died after oviposition, thus suggesting a very low incidence of mortality rates dueto starvation and reproductive costs. A case of long-term sperm storage deriving from autumnal mating is described. Population size estimates are provided for both study areas. Key words: Natrix maura, Ecology, Mediterranean region, Sardinia.Aspects of general ecology and population biology of two populations of freeliving viperine snakes (Natrix maura) were studied in Mediterranean localities of the island of Sardinia (Thyrrenian Sea, Italy). The apparent adult sex-ratio was not significantly different from equality, but males were slightly more numerous than females. The diet consisted mainly of arnphibians, both adults and tadpoles (area A) or fish (area B). Females were significantly longer than males. Reproduction was yearly, and clutch size and female total length were positively correlated. A hundred and seven live offsprings were obtained from 135 eggs (79.2% of successful incubation rates). The proportion of unsuccessful incubation was not significantly correlated with either female total length or clutch size. There was no evidence of a trade-off between clutch size and offspring size, as hatchlings were no smaller in clutches that were unusually large in relation to maternal body size. Oviposition date was correlated with neither maternal length nor clutch size. lncubation period was significantly correlated with mean hatchling size, but not with either clutch size or maternal length. No female died after oviposition, thus suggesting a very low incidence of mortality rates dueto starvation and reproductive costs. A case of long-term sperm storage deriving from autumnal mating is described. Population size estimates are provided for both study areas. Key words: Natrix maura, Ecology, Mediterranean region, Sardinia.Aspects of general ecology and population biology of two populations of freeliving viperine snakes (Natrix maura) were studied in Mediterranean localities of the island of Sardinia (Thyrrenian Sea, Italy). The apparent adult sex-ratio was not significantly different from equality, but males were slightly more numerous than females. The diet consisted mainly of arnphibians, both adults and tadpoles (area A) or fish (area B). Females were significantly longer than males. Reproduction was yearly, and clutch size and female total length were positively correlated. A hundred and seven live offsprings were obtained from 135 eggs (79.2% of successful incubation rates). The proportion of unsuccessful incubation was not significantly correlated with either female total length or clutch size. There was no evidence of a trade-off between clutch size and offspring size, as hatchlings were no smaller in clutches that were unusually large in relation to maternal body size. Oviposition date was correlated with neither maternal length nor clutch size. lncubation period was significantly correlated with mean hatchling size, but not with either clutch size or maternal length. No female died after oviposition, thus suggesting a very low incidence of mortality rates dueto starvation and reproductive costs. A case of long-term sperm storage deriving from autumnal mating is described. Population size estimates are provided for both study areas. Key words: Natrix maura, Ecology, Mediterranean region, Sardinia

Disentangling elastic and inelastic scattering pathways in the intersubband electron dynamics of n -type Ge/SiGe quantum fountains

n-type Ge/SiGe quantum wells have been suggested as a promising platform for the realization of a Si-compatible THz laser. Focusing on this material system, we have developed a numerical model to describe the intersubband carrier dynamics which restores the equilibrium after pulsed optical excitation in asymmetric coupled Ge/SiGe quantum wells. We take into account inelastic and elastic scattering processes and investigate different quantum-well geometries, doping densities, and excitation regimes. In this configuration space, we disentangle the effect on the overall dynamics of each scattering channel and provide intersubband relaxation times, finding larger values with respect to III-V based materials, thanks to the weaker electron-phonon coupling with respect to III-V compounds. Finally, the model is used to study and optimize the population inversion between the first- and second-excited subband levels and to assess its dependence on the lattice temperature, providing a sound theoretical framework to guide forthcoming experiments

Analysis of LINE1 Retrotransposons in Huntington’s Disease

Transposable elements (TEs) are mobile genetic elements that made up about half the human genome. Among them, the autonomous non-LTR retrotransposon long interspersed nuclear element-1 (L1) is the only currently active TE in mammals and covers about 17% of the mammalian genome. L1s exert their function as structural elements in the genome, as transcribed RNAs to influence chromatin structure and as retrotransposed elements to shape genomic variation in somatic cells. L1s activity has been shown altered in several diseases of the nervous system. Huntington disease (HD) is a dominantly inherited neurodegenerative disorder caused by an expansion of a CAG repeat in the HTT gene which leads to a gradual loss of neurons most prominently in the striatum and, to a lesser extent, in cortical brain regions. The length of the expanded CAG tract is related to age at disease onset, with longer repeats leading to earlier onset. Here we carried out bioinformatic analysis of public RNA-seq data of a panel of HD mouse models showing that a decrease of L1 RNA expression recapitulates two hallmarks of the disease: it correlates to CAG repeat length and it occurs in the striatum, the site of neurodegeneration. Results were then experimentally validated in HttQ111 knock-in mice. The expression of L1-encoded proteins was independent from L1 RNA levels and differentially regulated in time and tissues. The pattern of expression L1 RNAs in human HD post-mortem brains showed similarity to mouse models of the disease. This work suggests the need for further study of L1s in HD and adds support to the current hypothesis that dysregulation of TEs may be involved in neurodegenerative diseases

Tuning the doping of epitaxial graphene on a conventional semiconductor via substrate surface reconstruction

Combining scanning tunneling microscopy and angle-resolved photoemission spectroscopy, we demonstrate how to tune the doping of epitaxial graphene from p to n by exploiting the structural changes that occur spontaneously on the Ge surface upon thermal annealing. Furthermore, using first-principle calculations, we build a model that successfully reproduces the experimental observations. Since the ability to modify graphene electronic properties is of fundamental importance when it comes to applications, our results provide an important contribution toward the integration of graphene with conventional semiconductors