Effect of short- and long-range scattering in the conductivity of graphene: Boltzmann approach vs tight-binding calculations

We present a comparative study of the density dependence of the conductivity of graphene sheets calculated in the tight-binding (TB) Landauer approach and on the basis of the Boltzmann theory. The TB calculations are found to give the same density dependence of the conductivity, $\sigma \sim n$, for short-range and long-range Gaussian scatterers. In the case of short-range scattering the TB calculations are in agreement with the predictions of the Boltzmann theory going beyond the Born approximation, but in qualitative and quantitative disagreement with the standard Boltzmann approach within the Born approximation, predicting $\sigma=$ const. Even for the long-range Gaussian potential in a parameter range corresponding to realistic systems the standard Boltzmann predictions are in quantitative and qualitative disagreement with the TB results. This questions the applicability of the standard Boltzmann approach within the Born approximation, commonly used for the interpretation of the results of experimental studies of the transport in graphene.Comment: 5 page

Influence of nonmagnetic dielectric spacers on the spin wave response of one-dimensional planar magnonic crystals

The one-dimensional planar magnonic crystals are usually fabricated as a sequence of stripes intentionally or accidentally separated by non-magnetic spacers. The influence of spacers on shaping the spin wave spectra is complex and still not completely clarified. We performed the detailed numerical studies of the one-dimensional single- and bi-component magnonic crystals comprised of a periodic array of thin ferromagnetic stripes separated by non-magnetic spacers. We showed that the dynamic dipolar interactions between the stripes mediated by non-magnetic spacer, even ultra-narrow, significantly shift up the frequency of the ferromagnetic resonance and simultaneously reduce the spin wave group velocity, which is manifested by the flattening of the magnonic band. We attributed these changes in the spectra to the modifications of dipolar pinning and shape anisotropy both dependent on the width of the spacers and the thickness of the stripes, as well as to the dynamical magnetic volume charges formed due to inhomogeneous spin wave amplitude

Collisional properties of cold spin-polarized nitrogen gas: theory, experiment, and prospects as a sympathetic coolant for trapped atoms and molecules

We report a combined experimental and theoretical study of collision-induced dipolar relaxation in a cold spin-polarized gas of atomic nitrogen (N). We use buffer gas cooling to create trapped samples of 14N and 15N atoms with densities 5+/-2 x 10^{12} cm-3 and measure their magnetic relaxation rates at milli-Kelvin temperatures. Rigorous quantum scattering calculations based on accurate ab initio interaction potentials for the 7Sigma_u electronic state of N2 demonstrate that dipolar relaxation in N + N collisions occurs at a slow rate of ~10^{-13} cm3/s over a wide range of temperatures (1 mK to 1 K) and magnetic fields (10 mT to 2 T). The calculated dipolar relaxation rates are insensitive to small variations of the interaction potential and to the magnitude of the spin-exchange interaction, enabling the accurate calibration of the measured N atom density. We find consistency between the calculated and experimentally determined rates. Our results suggest that N atoms are promising candidates for future experiments on sympathetic cooling of molecules.Comment: 48 pages, 17 figures, 3 table

Cold heteromolecular dipolar collisions

We present the first experimental observation of cold collisions between two different species of neutral polar molecules, each prepared in a single internal quantum state. Combining for the first time the techniques of Stark deceleration, magnetic trapping, and cryogenic buffer gas cooling allows the enhancement of molecular interaction time by 10$^5$. This has enabled an absolute measurement of the total trap loss cross sections between OH and ND$_3$ at a mean collision energy of 3.6 cm$^{-1}$ (5 K). Due to the dipolar interaction, the total cross section increases upon application of an external polarizing electric field. Cross sections computed from \emph{ab initio} potential energy surfaces are in excellent agreement with the measured value at zero external electric field. The theory presented here represents the first such analysis of collisions between a $^2\Pi$ radical and a closed-shell polyatomic molecule.Comment: 7 pages, 5 figure

Transition from ballistic to diffusive behavior of graphene ribbons in the presence of warping and charged impurities

We study the effects of the long-range disorder potential and warping on the conductivity and mobility of graphene ribbons using the Landauer formalism and the tight-binding p-orbital Hamiltonian. We demonstrate that as the length of the structure increases the system undergoes a transition from the ballistic to the diffusive regime. This is reflected in the calculated electron density dependencies of the conductivity and the mobility. In particular, we show that the mobility of graphene ribbons varies as mu(n) n^(-lambda), with 0<lambda<0.5. The exponent lambda depends on the length of the system with lambda=0.5 corresponding to short structures in the ballistic regime, whereas the diffusive regime lambda=0 (when the mobility is independent on the electron density) is reached for sufficiently long structures. Our results can be used for the interpretation of experimental data when the value of lambda can be used to distinguish the transport regime of the system (i.e. ballistic, quasi-ballistic or diffusive). Based on our findings we discuss available experimental results

ВИВЧЕННЯ КЛАСИФІКАЦІЇ ІММУНОСЕНСОРІВ З ПОГЛЯДУ НА МЕДИЧНІ ЗАВДАННЯ

Immunosensors and immunotests are commonly used in medicine, where blood, urine or saliva samples enable concentrations of morphine, progesterone, estradiol, dopamine, insulin to be determined.In this work, the use of immunosensors for the following medical problems is considered: for the quantitative detection of alpha-fetoprotein, for determination of p53 protein in urine for diagnostics bladder cancer, for amperometric determination of carcinoembryonic antigen, for the determination of galectin-3, as biomarker of heart failure, for detecting hepatitis B surface antigen, for sensitive detection of tumor marker for determination of serum level in breast cancer patients.Иммуносенсоры и иммунотесты широко используются в медицине, где образцы крови, мочи или слюны позволяют определять концентрации морфина, прогестерона, эстрадиола, дофамина, инсулина.В данной работе рассматривается использование иммуносенсоров для следующих медицинских проблем: количественного определения альфа-фетопротеина, определения белка р53 в моче с целью диагностики рака мочевого пузыря, амперометрического определения карциноэмбрионального антигена, определения галектина-3 как биомаркера сердечной недостаточности, выявления поверхностного антигена гепатита В, чувствительного детектирования маркера опухоли при определении уровня в сыворотке крови пациентов с раком молочной железы.Імуносенсори та іммунотести широко використовують в медицині, де зразки крові, сечі або слини дозволяють визначати концентрації морфіну, прогестерону, естрадіолу, дофаміну, інсуліну.В роботі розглядається використання імуносенсорів для таких медичних проблем, як кількісне визначення альфа-фетопротеїну, визначення білка р53 в сечі з метою діагностики раку сечового міхура, амперометричне визначення карциноембріонального антигену, визначення галектину-3 як біомаркера серцевої недостатності, виявлення поверхневого антигену гепатиту В, чутливе детектування маркера пухлини при визначенні рівня у сироватці крові пацієнтів з раком молочної залози

ПРИНЦИПИ, МЕТОДИ ТА ГАЛУЗІ МЕДИКО-БІОЛОГІЧНИХ ЗАСТОСУВАНЬ ОПТИЧНИХ ІМУНОСЕНСОРІВ

The article is devoted to research of the basic principles of design and physical and biological methods of use of optical immunosensors. We investigate the main application of optical immunosensors in biology and medicine including testing food quality, natural environment protection, medical diagnostics.Статья посвящена исследованию основных принципов проектирования и физико-биологических методов использования оптических иммуносенсоров. Мы исследуем основные пути применения оптических иммуносенсоров в биологии и медицине, включая тестирование качества пищевых продуктов, защиту окружающей среды, медицинскую диагностику.Стаття присвячена дослідженню основних принципів проектування та фізико-біологічних методів використання оптичних імуносенсорів. Ми досліджуємо основні шляхи застосування оптичних імуносенсорів у біології та медицині, включаючи тестування якості харчових продуктів, захист природного середовища, медичну діагностику