Главная Новые поступления Описание Шлюз Z39.50

Базы данных


Труды сотрудников Института теплофизики УрО РАН - результаты поиска

Вид поиска
Каталог книг и продолжающихся изданий
Сводный каталог иностранных периодических изданий, имеющихся в библиотеках УрО РАН
Сводный каталог отечественных периодических изданий, имеющихся в библиотеках УрО РАН
Каталог диссертаций и авторефератов диссертаций УрО РАН
Каталог препринтов УрО РАН (1975 г. - )
Имидж-каталог отечественных книг (до 2010 г.)
Имидж-каталог иностранных книг (до 2010 г.)
Алфавитно-предметный указатель (АПУ) ЦНБ УрО РАН
Публикации об УрО РАН
Изобретения уральских ученых
Интеллектуальная собственность (статьи из периодики)
Нанотехнологии
Демидовские премии
Гибель династии Романовых
История Урала
Личная библиотека С. В. Вонсовского
Книжная коллекция Шубиных
Труды Института высокотемпературной электрохимии УрО РАН
Труды Института истории и археологии УрО РАН
Труды сотрудников Института горного дела УрО РАН
Труды сотрудников Института органического синтеза УрО РАН
Труды сотрудников Института теплофизики УрО РАН
Труды сотрудников Института химии твердого тела УрО РАН
Расплавы
Труды сотрудников ЦНБ УрО РАН
Публикации Черешнева В.А.
Публикации Чарушина В.Н.
Каталог библиотеки ИЭРиЖ УрО РАН
Электронная энциклопедия «Дискурсология»
Библиометрия
Область поиска
в найденном
 Найдено в других БД:Каталог книг и продолжающихся изданий (1)Публикации об УрО РАН (1)
Формат представления найденных документов:
полныйинформационныйкраткий
Отсортировать найденные документы по:
авторузаглавиюгоду изданиятипу документа
Поисковый запрос: (<.>A=Ермаков, Герман Викторович$<.>)
Общее количество найденных документов : 52
Показаны документы с 1 по 20
 1-20    21-40   41-52 
1.
Инвентарный номер: нет.
   
   S 68

    Smolyak, B. M.
    Retardation of the Magnetic Relaxation in High-Temperature Superconductors Near a Ferromagnet / B. M. Smolyak, G. V. Ermakov, M. S. Zakharov // Journal of Superconductivity and Novel Magnetism. - 2011. - Vol.24, №1-2. - С. 325-329
ББК 53
Рубрики: ФИЗИКА
Кл.слова (ненормированные):
HIGH-T C SUPERCONDUCTORS -- TRAPPED FLUX -- MAGNETIC RELAXATION
Аннотация: The creep of a magnetic flux trapped in a bulk high-temperature superconductor has been studied. It has been found that the magnetic relaxation is retarded when the superconductor is placed near a ferromagnet. The value of the retardation effect depends on the sequence of magnetization and the approach of the superconductor to a ferromagnet. The magnetic relaxation is fully suppressed when a superconducting sample first is magnetized and then is brought close to a ferromagnet. An interpretation of this effect has been discussed. Being magnetized, a ferromagnet produces its own magnetic field. While penetrating into a disk sample through its planes, the ferromagnet field induces screening currents, which circulate oppositely to the current that arises upon trapping of the magnetic flux. As a result, the stability of the magnetic structure is sharply improved since opposite driving forces can act on different sections of the vortices

Найти похожие
2.
Инвентарный номер: нет.
   
   G 95

    Gurashkin, A. L
    Experimental study of the kinetics of boiling and superheating boundary of n-hexane in rigid powder structures [Текст] / A. L Gurashkin, S. A. Perminov, G. V. Ermakov // Teplofizika i Aeromekhanika. - 2006. - Vol. 13, № 4. - С. 641-650
ББК 53
Рубрики: ФИЗИКА
Кл.слова (ненормированные):
N-HEXANE

Найти похожие
3.
Инвентарный номер: нет.
   
   S 68

    Smolyak, B. M.
    The paramagnetic effect of clusters in granular superconductors under the Meissner magnetization [Text] / B. M. Smolyak, G. V. Ermakov // Journal of Magnetism and Magnetic Materials. - 1996. - Vol. 153, № 3. - P311-314
ББК 53
Рубрики: ФИЗИКА
Кл.слова (ненормированные):
ЭФФЕКТ ПАРАМАГНИТНЫЙ -- ПУЧКИ СВЕРХПРОВОДНИКОВ -- СВЕРХПРОВОДНИК ГРАНУЛИРОВАННЫЙ -- НАМАГНИЧЕННОСТЬ МЕЙСНЕРА

Найти похожие
4.
Инвентарный номер: нет.
   
   S 68

    Smolyak, B. M.
    Effects of relaxation in levitating superconductors / B. M. Smolyak, G. N. Perelshtein, G. V. Ermakov (Yermakov) // Cryogenics. - 2002. - Vol.42, №10. - С. 635-644
ББК 53
Рубрики: ФИЗИКА
Кл.слова (ненормированные):
SUPERCONDUCTORS -- FLUX CREEP -- MAGNETIC LEVITATION
Аннотация: The effect of the magnetic flux creep on the levitation stability of high-temperature superconductors was studied. It was shown experimentally that under a unipolar magnetization the levitation force decreased at a logarithmic velocity characteristic of the creep process. If the current structure was bi- or multi-polar one, which was formed in a sample exposed to a reversing external magnetic field, the force remained unchanged during a certain period of time. The theory of relaxation of magnetization and force for a partial and full penetration of the critical state was considered. It was shown that relaxation decelerated sharply if the region with a current producing the main magnetization was far from the superconductor surface. A concept of an open and internal magnetic relaxation was introduced. The time of the internal relaxation for different reverse depths was estimated. The calculated values approached the experimental values of the levitation stabilization time

Найти похожие
5.
Инвентарный номер: нет.
   
   E 70

    Ermakov, G. V.
    Homogeneous Boundary of the Attainable Superheat of Liquids by the “Theory of Surges” / G. V. Ermakov, M. A. Parshakova, E. V. Lipnyagov // Journal of Physical Chemistry B. - 2001. - Vol.105, №3. - С. 696-701
ББК 53
Рубрики: ФИЗИКА
Кл.слова (ненормированные):
HOMOGENEOUS NUCLEATION -- DORING−VOLMER−FRENKEL−ZELDOVICH−KAGAN THEORY -- TOLMAN LENGTH
Аннотация: An alternative theory of homogeneous nucleation based on the theorem on surges has been formulated. This theory gives a steeper temperature dependence of the homogeneous nucleation rate along isobars than that given by the classical Doring−Volmer−Frenkel−Zeldovich−Kagan theory. By the alternative theory, lines of attainable superheat lie much higher than classical ones and are close to the spinodal. Taking into account the dependence of the surface tension on r, i.e., the nucleus radius of curvature, assuming the power dependence of the Tolman length, δ = const/rn, from the theories for different liquids the boundary of attainable superheats moves toward lower temperatures

Найти похожие
6.
Инвентарный номер: нет.
   
   S 68

    Smolyak, B. M.
    Elimination of magnetic relaxation in superconductors on approaching a ferromagnet / B. M. Smolyak, G. V. Ermakov // Physica C. - 2010. - Vol.470, №3. - С. 218-220
ББК 53
Рубрики: ФИЗИКА
Кл.слова (ненормированные):
MAGNETIC RELAXATION -- FERROMAGNET -- MAGNETIC STRUCTURE
Аннотация: It is found that magnetic relaxation is suppressed in a high-temperature superconductor when it approaches a ferromagnet. It is supposed that this phenomenon results from formation of a nonequilibrium magnetic structure, in which counter driving forces act in different regions

Найти похожие
7.
Инвентарный номер: нет.
   
   Э 45

   
    Электрофизические свойства керамики состава Bi1, 8Ca1, 8Sr1, 8Cu2, 2Oy и Bi2CaO, 67SrO, 23Cu2Oy в зависимости от условий термообработки [] / В. А. Фотиев, Б. В. Слободин, М. А. Пахомова, Е. В. Пострехин, Б. М. Смоляк, Г. В. Ермаков // Физико-химические основы получения высокотемпературных сверхпроводящих материалов: Информ. материалы. - 1989. - С. 98-103
ББК 53
Рубрики: ФИЗИКА
Кл.слова (ненормированные):
КЕРАМИКА -- СВОЙСТВА ЭЛЕКТРОФИЗИЧЕСКИЕ -- ТЕРМООБРАБОТКА КЕРАМИКИ -- Bi1 -- 8Ca1 -- 8Sr1 -- 8Cu2 -- 2Oy -- Bi2CaO -- 67SrO -- 23Cu2Oy -- ВИСМУТ -- Bi -- КАЛЬЦИЙ -- Ca -- СТРОНЦИЙ -- Sr -- МЕДЬ -- Cu -- КИСЛОРОД -- O (КИСЛОРОД)

Найти похожие
8.
Инвентарный номер: нет.
   
   Б 33

    Башкатов, Н. В.
    Уравнение состояния перегретых жидких ацетона и n-гексана [] / Н. В. Башкатов, Т. А. Бебенина, Г. В. Ермаков // Теплофизика высоких температур. - 1982. - Т.20, N2. - С. 380-382
ББК 53
Рубрики: ФИЗИКА
Кл.слова (ненормированные):
АЦЕТОН ЖИДКИЙ -- n-ГЕКСАН ЖИДКИЙ -- УРАВНЕНИЕ СОСТОЯНИЯ -- n-ГЕКСАН ПЕРЕГРЕТЫЙ -- АЦЕТОН ПЕРЕГРЕТЫЙ -- УРАВНЕНИЕ СОСТОЯНИЯ

Найти похожие
9.
Инвентарный номер: нет.
   
   S 68

    Smolyak, B. M.
    ZFC-, FC- and Rem- susceptibility of granular superconductors [Text] / B. M. Smolyak, E. V. Postrekhin, G. V. Ermakov // Superconductor Science and Technology. - 1994. - V. 7. - P427-433
ББК 53
Рубрики: ФИЗИКА
Кл.слова (ненормированные):
ZFC-ЧУВСТВИТЕЛЬНОСТЬ -- FC-ЧУВСТВИТЕЛЬНОСТЬ -- Rem-ЧУВСТВИТЕЛЬНОСТЬ -- СВЕРХПРОВОДНИКИ ЗЕРНИСТЫЕ -- ЗЕРНИСТЫЕ СВЕРХПРОВОДНИКИ -- ТЕПЛОФИЗИКА

Найти похожие
10.
Инвентарный номер: нет.
   
   T 44

   
    The Instability of Levitation of High-Temperature Superconductors Subject to an Alternating Magnetic-Field [Text] / B. M. Smolyak, M. V. Babanov, G. V. Ermakov, I. B. Smolyak, S. V. Naumov // Physica A. - 1998. - V. 302, Iss. 1. - P23-30
ББК 53
Рубрики: ФИЗИКА
Кл.слова (ненормированные):
ПОЛЕ МАГНИТНОЕ -- МАГНИТНОЕ ПОЛЕ -- ПОЛЕ ПЕРЕМЕННОЕ -- ПЕРЕМЕННОЕ ПОЛЕ -- ЛЕВИТАЦИЯ -- НЕУСТОЙЧИВОСТЬ ЛЕВИТАЦИИ -- ЛЕВИТАЦИИ НЕУСТОЙЧИВОСТЬ -- СВЕРХПРОВОДНИКИ ВЫСОКОТЕМПЕРАТУРНЫЕ -- ВЫСОКОТЕМПЕРАТУРНЫЕ СВЕРХПРОВОДНИКИ

Найти похожие
11.
Инвентарный номер: нет.
   
   T 44

   
    The effect of an Alternating Magnetic-Field on the Stability of Hard Levitation of High-Temperature Superconductors [Text] / B. M. Smolyak, M. V. Babanov, G. V. Ermakov, E. V. Postrekhin, L. M. Shou, I. B. Smolyak, S. V. Naumov // Materials Science and Engineering B. Solid State Materials for Advanced Technology. - 1998. - V. 53, Iss. 1-2. - P177-181
ББК 53
Рубрики: ФИЗИКА
Кл.слова (ненормированные):
ПОЛЕ МАГНИТНОЕ -- ПОЛЕ ПЕРЕМЕННОЕ -- ЛЕВИТАЦИЯ ТЯЖЕЛАЯ -- СВЕРХПРОВОДНИКИ ВЫСОКОТЕМПЕРАТУРНЫЕ

Найти похожие
12.
Инвентарный номер: нет.
   
   S 93

   
    Superheated liquids: Thermophysical properties, homogeneous nycleation and explosive boiling [Text] / V. P. Skripov, V. G. Baidakov, E. N. Sinitsin, N. I. Danilov, G. V. Ermakov, N. V. Bulanov, P. A. Pavlov, E. D. Nikitin // AIChE - ASME Heat Transfer Conference (Salt Lake City, Utah, 1977, 15-17 Aug.: 77-HT-87 ASME publication, United engineering center, 345). - 1977. - C. Up. - P1-12
ББК 53
Рубрики: ФИЗИКА
Кл.слова (ненормированные):
ЖИДКОСТИ ПЕРЕГРЕТЫЕ -- ПЕРЕГРЕТЫЕ ЖИДКОСТИ -- СВОЙСТВА ТЕРМОФИЗИЧЕСКИЕ -- ТЕРМОФИЗИЧЕСКИЕ СВОЙСТВА -- ЗАРОДЫШЕОБРАЗОВАНИЕ ГОМОГЕННОЕ -- ГОМОГЕННОЕ ЗАРОДЫШЕОБРАЗОВАНИЕ -- КИПЕНИЕ ВЗРЫВЧАТОЕ -- ВЗРЫВЧАТОЕ КИПЕНИЕ -- ТЕПЛОФИЗИКА -- КОНФЕРЕНЦИИ -- ДОКЛАДЫ

Найти похожие
13.
Инвентарный номер: нет.
   
   P 28

    Parshakova, M. A.
    Nucleation as a local subsystem fluctuation / M. A. Parshakova, G. V. Ermakov // Physica A. - 2002. - Vol.303, №1-2. - С. 35-47
ББК 53
Рубрики: ФИЗИКА
Кл.слова (ненормированные):
RANDOM SYSTEMS -- NUCLEATION -- FLUCTUATION
Аннотация: A nucleation theory has been advanced, in which a metastable system is considered as the sum of statistically independent subsystems. This theory provides a flexible scheme taking into account actually all initiating factors, including even a separate “weak” point in a system. In the case of a homogeneous nucleation, the difference between the classical and alternative approaches consists in the expression for the preexponential. Depending on the diameter of the critical nucleus, numerical estimates of this preexponential by the two theories differ by 0–4 orders of magnitude for a supersaturated steam and 1–5 orders of magnitude for a superheated liquid

Найти похожие
14.
Инвентарный номер: нет.
   
   E 97

   
    Experimental determination of superheated liquid density by the optical fiber method [Electronic resource] / A. L Gurashkin, A. A. Starostin, A. A. Uimin, A. D. Yampol'skiy, G. V. Ermakov, P. V. Skripov // Journal of Engineering Thermophysics. - 2013. - Vol.22, №3. - P194-202. - Bibliogr. : p. 202 (21 ref.)
ББК 53
Рубрики: ФИЗИКА
Кл.слова (ненормированные):
OPTICAL FIBER METHOD -- SUPERHEATED LIQUID DENSITY -- LIQUID-VAPOR
Аннотация: An experimental approach to determination of the density of liquid superheated with respect to the liquid-vapor equilibrium temperature, including the range of high degrees of superheating, is developed. The approach is based on application of an optical fiber method combined with a pure bubble chamber. Performance of the method for investigation of the refractive index and density for superheated liquids as functions of temperature and pressure is illustrated in experiments with n-hexane as a reference substance for thermophysical measurements. The relative density measurements are performed with a resolution up to 10-4 at a characteristic time of 1 ms. For absolute measurements, the setup should be calibrated by the known data on the liquid density for the saturation line

\\\\expert2\\NBO\\Journal of Engineering Thermophysics\\2013, V.22, N 3. P. 194-202.pdf
Найти похожие
15.
Инвентарный номер: нет.
   
   E 97

   
    Experimental determination of superheated liquids boiling-up expectancy time probabilities distribution [Electronic resource] / E. V. Lipnyagov, S. A. Perminov, G. V. Ermakov, B. M. Smolyak // Thermophysics and Aeromtchanics. - 2009. - Vol.16, №4. - P627-633. - Bibliogr. : p. 633 (16 ref.)
ББК 53
Рубрики: ФИЗИКА
Кл.слова (ненормированные):
LIQUID -- N-PENTANE -- BOILING-UP
Аннотация: Results of statistical measurement of n-pentane and n-hexane boiling-up expectancy time near the boundary of attainable superheating are presented. Experiments were carried out in glass capillaries with various volumes of superheated liquid. Several samples with the volume from 100 to 200 measurements of life time for preset metastable state have been obtained (p, T = const). Their histograms contain small empty initial section, maximum and long “tail” in the area of large times. Non-monotonous dependence of probability distribution density on time proves non-stationary character of the random process resulting in the production of supercritical embryo. Two simple approximations of non-stationary nucleation flow well describing experimental data have been considered. For exponential distribution, the probabilities of experimentally found peculiarities of boiling-up expectancy time distribution density have been evaluated; they prove incompatibility of this distribution with the experimental one

\\\\expert2\\NBO\\Thermophysics and Aeromechanics\\2009, V. 16, N 4. P. 627-633.pdf
Найти похожие
16.
Инвентарный номер: нет.
   
   E 97

   
    Experimental testing of liquid boiling-up homogeneity near the boundary of the attainable superheating [Electronic resource] / E. V. Lipnyagov, S. A. Perminov, G. V. Ermakov, B. M. Smolyak // Thermophysics and Aeromtchanics. - 2009. - Vol.16, №3. - P445-457. - Bibliogr. : p. 457 (20 ref.)
ББК 53
Рубрики: ФИЗИКА
Кл.слова (ненормированные):
SUPERHEATING -- LIQUID -- N-PENTANE
Аннотация: Results of measured average expectancy time of n-pentane and n-hexane boiling-up to the boundary of attainable superheating are presented. Experiments have been carried out in glass capillaries with substantially decreasing value of the superheated liquid volume for the preset metastable state (p, T = const). Obtained data fail to prove correlation 1 JVῑ = following from the condition of homogeneity and stationarity of the random process resulting in the superheated liquid boiling-up (J is the frequency of homogenous nucleation, V is the volume of the superheated liquid, ῑ is the average life time). Thus, experiments on superheated liquid boiling-up kinetics bound with measurements of average life time in glass capillaries cannot serve a proof of the validity of classical theory of nucleation for superheated liquids since one of the ground conditions — boiling-up homogeneity — is not met

\\\\expert2\\NBO\\Thermophysics and Aeromechanics\\2009, V. 16, N 3. P. 445-457.pdf
Найти похожие
17.
Инвентарный номер: нет.
   
   Z 19

    Zakharov, M. S.
    Effect of External Nonuniform Magnetic Field on Flux Creep Process in Superconductor [Electronic resource] / M. S. Zakharov, B. M. Smolyak, G. V. Ermakov // Journal of Superconductivity and Novel Magnetism. - 2012. - Article in Press. - P1-4
ББК 53
Рубрики: ФИЗИКА
Кл.слова (ненормированные):
CRITICAL STATE -- MAGNETIC RELAXATION -- SUPERCONDUCTORS
Аннотация: The effect of an external nonuniform magnetic field on the flux creep rate in a high-temperature superconductor with trapped magnetic flux was studied. The magnetic relaxation was suppressed when the superconductor was put into a field of permanent magnets or when it approached a ferromagnet. The effect arises when the field sources (being magnetized, the ferromagnet produces its own field) are placed near the superconductor surface, where the flux line ends are located. For these cases, we carried out the calculations of vortex and current density distributions, which demonstrate that reverse currents flow in the near-surface regions of the sample. This verifies the hypothesis suggested earlier about the influence of counter Lorentz forces retarding the creep of the vortices. In the interpretation of the results, we also take into consideration the magnetic force acting on the vortex ends in the external nonuniform magnetic field that allows us to explain the experimental results, in which the current structure in the sample is unipolar

Найти похожие
18.
Инвентарный номер: нет.
   
   S 81

   
    Statistical properties of fluctuation boiling centers on the wall of a silylated glass cell for n-pentane near the boundary of attainable superheat [Electronic resource] / S. A. Perminov, E. V. Lipnyagov, G. V. Ermakov, M. A. Parshakova // International Journal of Heat and Mass Transfer. - 2013. - Vol.57, №1. - P429-431. - Bibliogr. : p. 431 (11 ref.)
ББК 53
Рубрики: ФИЗИКА
Кл.слова (ненормированные):
BOILING-UP -- HETEROGENEOUS -- LIQUIDS
Аннотация: High-speed video has been first used to show visually the existence of reproducible fluctuation boiling centers on a solid wall of an experimental cell for liquids superheated to the attainable superheat boundary. The main statistical characteristics of fluctuation centers have been calculated with allowance for censoring. The nonstationarity of a fluctuation process leading to the appearance of a nucleus capable of spontaneous growth has been shown. The change in the density of distribution of probabilities of boiling-up on an ensemble of centers with an increase in their number has been demonstrated. With an increase in the number of centers the probability of observation of large lifetimes of a liquid in the state of superheating decreases rapidly

\\\\expert2\\NBO\\International Journal of Heat and Mass Transfer\\2013, v.57, p.429-431.pdf
Найти похожие
19.
Инвентарный номер: нет.
   
   T 44

   
    The visualization of boiling-up onset of superheated n-pentane in a glass capillary at atmospheric pressure by high-speed video [Electronic resource] / E. V. Lipnyagov, M. A. Parshakova, S. A. Perminov, G. V. Ermakov // International Journal of Heat and Mass Transfer. - 2013. - Vol.60, №1. - P612-615. - Bibliogr. : p. 615 (12 ref.)
ББК 53
Рубрики: ФИЗИКА
Кл.слова (ненормированные):
BOILING-UP -- BUBBLES -- HIGH-SPEED VIDEO
Аннотация: Experimental study of boiling-up of superheated n-pentane at atmospheric pressure in a glass capillary was carried out by high-speed video. From a visual comparison of video frames, we consider the character of vaporization in three temperature ranges corresponding to the following areas of the temperature dependence of the mean lifetime of metastable state: low temperature descending section, "plateau", and boundary of attainable superheat. Temperature at the boundary of attainable superheat was about 2 °C lower than the maximum values reported in the literature and achieved in the more narrow capillaries and 2.5 °C lower than at the homogeneous boundary of attainable superheat

\\\\expert2\\NBO\\International Journal of Heat and Mass Transfer\\2013, v.60, p.612-615.pdf
Найти похожие
20.
Инвентарный номер: нет.
   
   H 62

   
    Heterogeneous boiling-up of superheated liquid at achievable superheat threshold / G. V. Ermakov, E. V. Lipnyagov, S. A. Perminov, A. L Gurashkin // Journal of Chemical Physics. - 2009. - Vol.131, №3. - С. 031102
ББК 53
Рубрики: ФИЗИКА
Кл.слова (ненормированные):
HOMOGENEOUS NUCLEATION -- BOILING-UP -- LIQUID
Аннотация: The classical theory of homogeneous nucleation describes well the superheat threshold observed in experiments. It may be assumed therefore that homogeneous boiling-up of a liquid takes place in experiments, and the theory has been verified experimentally well. The streak photography used in this study showed that boiling-up of a superheated liquid at the threshold of the achievable superheat occurs at a limited number of surface fluctuation centers in a vessel, rather than in the bulk as one would expect with homogeneous nucleation. Thus, the homogeneous theory, which rather accurately describes the heterogeneous threshold of the achievable superheat, obviously is not confirmed in

Найти похожие
 1-20    21-40   41-52 
 
Описание базы данных
Стандартный
По словарю
Расширенный
ГРНТИ-навигатор
Статистика обращений

Сиглы отделов ЦНБ УрО РАН


  бр.ф. - Бронированный фонд

  бф - Научно-библиографический отдел

  БХЛ - Фонд художественной литературы

  ИИиА -Фонд исторической литературы в ЦНБ УрО РАН

  ИМЕТ -Отдел ЦНБ в Институте металлургии УрО РАН

  кх - Отдел фондов (книгохранениe)

  МБА - Межбиблиотечный абонемент

  мф - Методический фонд

  ок - Отдел научной каталогизации

  оку - Отдел комплектования и учета

  орф - Обменно-резервный фонд

  пф - Читальный зал деловой и патентной информации

  рк - Фонд редкой книги

  ч/з - Главный читальный зал

  эр - Зал электронных ресурсов

  

Сиглы библиотек институтов и НЦ УрО РАН
© Международная Ассоциация пользователей и разработчиков электронных библиотек и новых информационных технологий
(Ассоциация ЭБНИТ)
Яндекс.Метрика