A simple solid-on-solid model of epitaxial thin films growth: surface roughness and dynamics

The random deposition model must be enriched to reflect the variety of surface roughness due to some material characteristics of the film growing by vacuum deposition or sputtering. The essence of the computer simulation in this case is to account for possible surface migration of atoms just after the deposition, in connection with binding energy between atoms (as the mechanism provoking the diffusion) and/or diffusion energy barrier. The interplay of these two factors leads to different morphologies of the growing surfaces from flat and smooth ones, to rough and spiky ones. In this paper we extended our earlier calculation by applying some extra diffusion barrier at the edges of terrace-like structures, known as Ehrlich-Schwoebel barrier. It is experimentally observed that atoms avoid descending when the terrace edge is approach and these barriers mimic this tendency. Results of our Monte Carlo computer simulations are discussed in terms of surface roughness, and compared with other model calculations and some experiments from literature. The power law of the surface roughness $\sigma$ against film thickness $t$ was confirmed. The nonzero minimum value of the growth exponent $\beta$ near 0.2 was obtained which is due to the limited range of the surface diffusion and the Ehrlich-Schwoebel barrier. Observations for different diffusion range are also discussed. The results are also confronted with some deterministic growth models.Comment: 12 pages + 8 figures (to appear in Int. J. Mod. Phys. C, journal style applied

New algorithm for the computation of the partition function for the Ising model on a square lattice

A new and efficient algorithm is presented for the calculation of the partition function in the $S=\pm 1$ Ising model. As an example, we use the algorithm to obtain the thermal dependence of the magnetic spin susceptibility of an Ising antiferromagnet for a $8\times 8$ square lattice with open boundary conditions. The results agree qualitatively with the prediction of the Monte Carlo simulations and with experimental data and they are better than the mean field approach results. For the $8\times 8$ lattice, the algorithm reduces the computation time by nine orders of magnitude.Comment: 7 pages, 3 figures, to appear in Int. J. Mod. Phys.

A simple solid-on-solid model of epitaxial thin films growth: surface morphology anisotropy

In this paper we present a generalization of a simple solid-on-solid epitaxial model of thin films growth, when surface morphology anisotropy is provoked by anisotropy in model control parameters: binding energy and/or diffusion barrier. The anisotropy is discussed in terms of the height-height correlation function. It was experimentally confirmed that the difference in diffusion barriers yields anisotropy in morphology of the surface. We got antisymmetric correlations in the two in-plane directions for antisymmetric binding.Comment: 6 pages + 2 figures (to appear in Int. J. Mod. Phys. C, journal style applied

Effect of Topping Time on Dark Tobacco Yield

When the terminal bud is removed from tobacco by topping, a number of changes are triggered in the plant: increased root growth, nicotine synthesis, improved drought tolerance, and leaf expansion and increased thickness. These changes are affected by topping time; generally there will be less crop response to topping as topping is delayed. The most important changes, from a producer\u27s perspective, are continued leaf expansion and thickening, with a commensurate improvement in quality and increase in yield. Topping at the proper time of plant development is often difficult on a field scale since uneven crop growth, particularly when tobacco is set early using bare-root plants, causes delay or irregular blooming. Two major factors that can cause irregular plant growth are soil compaction, usually due to tilling soil that is too wet in the spring, and black root rot. Many producers wait until 50% or more of the plants are in bloom before topping. Research was conducted from 1989 through 1991 to determine the effects of topping time on dark tobacco yield and quality

Divergent evolution paths of different genetic families in the Penna model

We present some results of simulations of population growth and evolution, using the standard asexual Penna model, with individuals characterized by a string of bits representing a genome containing some possible mutations. After about 20000 simulation steps, when only a few genetic families are still present from among rich variety of families at the beginning of the simulation game, strong peaks in mutation distribution functions are observed. This known effect is due to evolution rules with hereditary mechanism. The birth and death balance in the simulation game also leads to elimination of families specified by different genomes. Number of families $G(t)$ versus time $t$ follow the power law, $G \propto t^n$. Our results show the power coefficient exponent $n$ is changing as the time goes. Starting from about --1, smoothly achieves about --2 after hundreds of steps, and finally has semi-smooth transition to 0, when only one family exists in the environment. This is in contrast with constant $n$ about --1 as found, for example, in \cite{bib:evolution}. We suspect that this discrepancy may be due to two different time scales in simulations - initial stages follow the $n\approx-1$ law, yet for large number of simulation steps we get $n\approx-2$, providing random initial population was sufficiently big to allow for still reliable statistical analysis. The $n\approx-1$ evolution stage seems to be associated with the Verhulst mechanism of population elimination due to the limited environmental capacity - when the standard evolution rules were modified, we observed a plateau ($n=0$) in the power law in short time scale, again followed by $n\approx -2$ law for longer times. The modified model uses birth rate controlled by the current population instead of the standard Verhulst death factor

Sucker Control Performance in Dark Tobacco

Poor sucker control adversely affects tobacco yield and quality. Suckers serve as a sink for nutrients and dry matter that otherwise would go to the expanding leaves intended for harvest, resulting in lower yields. Hand removal of large suckers can cause leaf damage, and failure to remove suckers may result in spoilage during the curing process, resulting in lowered quality. Use of chemical sucker control measures used in burley production can produce lower yields or W1desirable cured leaf color of dark tobacco. These studies were conducted to compare the effects of recommended sucker control practices for dark tobacco with systems being adopted in the dark tobacco production are

Dependence of the SWR Linewidth on the Wavevector in Amorphous Thin Films

Work supported in part by the Central Research Project 01.08.B.Zadanie pt. „Digitalizacja i udostępnienie w Cyfrowym Repozytorium Uniwersytetu Łódzkiego kolekcji czasopism naukowych wydawanych przez Uniwersytet Łódzki” nr 885/P-DUN/2014 zostało dofinansowane ze środków MNiSW w ramach działalności upowszechniającej naukę

Wyniki leczenia neurochirurgicznego gruczolaków kortykotropowych przysadki w zespole Nelsona — pułapki terapeutyczne

  Introduction: Nelson’s syndrome (NS) is a rare clinical syndrome caused by an enlarging, aggressive corticotroph pituitary adenoma that can occur following bilateral adrenalectomy performed in the treatment of refractory Cushing’s disease (CD). Such tumours respond poorly to currently available therapeutic options, which include surgery, radiotherapy, pharmacotherapy, and chemotherapy. They are a challenging problem in neurosurgical practice. The aim of this work was to evaluate the early and long-term results of microsurgery in a single surgeon’s series of patients with NS. Material and methods: During the period from January 2000 to December 2005, 10 patients with NS underwent surgery. The authors analysed surgical outcomes in the NS group of seven women and three men with the mean age of 47.99 years (range 39–66, SD ± 8.47 years). NS was diagnosed based on clinical signs and symptoms, especially hyperpigmentation of the skin, elevated serum ACTH levels, and pituitary tumour growth. Parasellar extension of the adenomas was assessed in both groups according to Knosp’s and Hardy-Wilson classifications. Pituitary function and radiographs were evaluated in the early postoperative period, 30 days after the operation, and during follow-up. Histological examination was based on the WHO (2004) criteria. Results: According to the criteria for Nelson’s syndrome remission, five patients (50%) were cured. No perioperative mortality was reported. Three patients developed pituitary insufficiency and two patients developed diabetes insipidus. There was one case of postoperative cerebrospinal fluid leakage. One patient was diagnosed with pituitary carcinoma. Conclusions: Transsphenoidal microsurgical removal of pituitary adenomas is a safe and effective treatment of Nelson’ syndrome. (Endokrynol Pol 2015; 66 (6): 504–513)    Wstęp: Zespół Nelsona (NS) to rzadko występująca jednostka chorobowa spowodowana agresywnym, inwazyjnym rozrostem gruczolaka kortykotropowego przysadki u pacjentów podanych obustronnej ratunkowej adrenalektomii w następstwie przetrwałej choroby Cushinga. Skuteczność dostępnym metod terapeutycznych: leczenia chirurgicznego, radioterapii, leczenia farmakologicznego i chemioterapii jest w tych przypadkach ograniczona. Leczenie chorych z NS pozostaje wyzwaniem w praktyce neurochirurgicznej. Celem pracy była ocena wczesnych i odległych wyników leczenia mikrochirurgicznego gruczolaków kortykotropowych przebiegających z objawami NS. Materiał i metody: Analizie poddano wyniki 10 chorych (7 kobiet i 3 mężczyzn, średnia wieku 47,99 lat (w zakresie 39–66, SD ± 8.47 lat) operowanych w okresie od stycznia 2000 do grudnia 2005 roku przez jednego chirurga. Zespół Nelsona rozpoznano na podstawie objawów klinicznych (hiperpigmentacji skóry i błon śluzowych), wyników badań biochemicznych (wysokie wartości ACTH w surowicy) oraz wzrostu gruczolaka przysadki. Okołosiodłowy rozrost guza przysadki oceniano na podstawie skali Knospa i Hardyego-Wilsona. Czynność hormonalną przysadki analizowano we wczesnym okresie pooperacyjnym, 30 dni po operacji oraz w okresie obserwacji odległej. Ocenę histopatologiczną przeprowadzono według wytycznych klasyfikacji WHO (2004). Wyniki: Remisję zespołu Nelsona uzyskano u 5 chorych. W analizowanej grupie nie było powikłań śmiertelnych w okresie okołooperacyjnym. Po operacji w 3 przypadkach wystąpiła niedoczynność przysadki, a moczówka prosta u 2 chorych. W jednym przypadku po operacji wystąpił płynotok pooperacyjny. U jednej chorej w okresie obserwacji stwierdzono ewolucję guza w rak przysadki. Wnioski: Leczenie mikrochirurgiczne gruczolaków przysadki w NS jest metodą skuteczną i bezpieczną. (Endokrynol Pol 2015; 66 (6): 504–513)