267
Спектры приведены для
EXC
= 0.51453 мкм, т. е. с энергией кванта, превышающей E
g
как
ZnTe (Eg = 2.39 эВ, 4.2 К), так и CdTe (Eg = 1.60 эВ, 4.2 К) и энергию рекомбинации
электронно-дырочных пар в квантовых ямах. Как видно из Рис., спектр LT PL состоит из
нескольких полос в экситонной области от буферного ZnTe эпитаксиального слоя, ЭС, и
доминирующей по интенсивности фотолюминесценции от квантовых ям, I
QW
: линии экситонов,
связанных либо на нейтральном доноре (или объемный поляритон [5]) I
2
Ga
(2,3736 эВ), либо на
нейтральном акцепторе I
1
/
(2,37 эВ); и неэлементарной полосы I
1
C
(2,3568 эВ), связанной с
дефектами [5]. На фоне спектра LT PL проявляется серия
узких (W ~ 2 мэВ) полос, сдвинутых
относительно частоты возбуждающего света на величину 208-211 см
-1
(кривые 2,3) умноженную
на n=1, 2, 3… Интенсивность полос в серии увеличивалась немонотонно, по мере приближения к
одной из резонансных полос (I
QW
, I
C
). Сдвиг между полосами в серии не зависел от длины волны
возбуждающего света и составлял величину ~ 210 см
-1
для исходного образца (кривая 1).
Измеренная нами величина продольного оптического фонона обьѐмных монокристаллов ZnTe
составила ~208см
-1
, а для CdTe ~169см
-1
. Т.е., наблюдаемые в спектре фононные повторения
соответствуют LO-фононам ZnTe барьера. Такое резонансное усиление интенсивности серии
узких полос на полосах излучения от квантовых ям, наблюдаемое в спектрах LT PL для квантово-
размерных структур CdZnSe/ZnSe в нтерпретировалось с использованием модели , согласно
которой горячие электроны, возбуждаемые светом в зоне проводимости, могут релаксировать с
испусканием одного за другим нескольких оптических фононов (т. н. ―каскадная модель‖). В
нашей работе частота оптического фонона для CdZnTe/ZnTe квантоворазмерных структур слабо
сдвинута в область больших частот по сравнению с объемным значением LO-фонона
монокристаллов ZnTe.
Таким образом, для гетеросистемы с квантово-размерными слоями на основе CdZnTe/ZnTe
показана возможность многофононной релаксации горячих электронов, образующихся при
оптическом возбуждении путем обмена энергии этих электронов с барьерным слоем с
испусканием LO-фононов (каскадный механизм). Изучение образцов, модифицированных
облучением высокоэнергетичными электронами и рентгеновскими лучами (с измененными
свойствами приповерхностного слоя, барьерного слоя и формы ям), позволило показать, что
резонанс частот (возбуждающего света и основных переходов в квантовых ямах) и степень
локализации экситона являются доминирующими факторами в наблюдении такого типа
процессов.
ЛИТЕРАТУРА
:
1.
Melnik N. N., Sadofyev Yu. G., Zavаritskaya T. N.// Abstr. of 9
th
Int. Conf. ―II-VI Compounds‖,
Kyoto, Japan, 1999.
2.
Seto S., Tanaka A., Takeda F., Matsuura K.// J.Cryst.Growth. 1994. V.138. N1. P.346-351.
3.
Козловский В. И., Крыса А. Б., Садофьев Ю. Г., Турьянский А. Г.// ФТП. 1999. Т. 33. В. 7,
С. 810-814.
4.
Dang Le Si., Cibert J., Gobil Y., Saminadayar K., Tatarenko S.// Appl. Phys. Lett.2000. V.55.
N3, P.235-237.
5.
Багаев В.С., Зайцев В.В., Калинин В.В. и др.// Письма в ЖЭТФ. 2011. Т.58. В.2. С.82-86.
ECOLOGICAL EFFECTS OF ENVIRONMENTAL STRESSORS
Allaniyazova M.K.
Doctor of Biological Sciences, Acting Professor
Organic and Inorganic Chemistry Department
Nukus, Uzbekistan
Arzuov R.
2
nd
year student, KarSU named after Berdakh
Nukus, Uzbekistan
Abstract
: Regimes of environmental stress are exceedingly complex. Particular stressors exist within
continua of intensity of environmental factors. Those factors interact with each other, and their
detrimental effects on organisms are manifest only at relatively high or low strengths of exposure—in
fact, many of them are beneficial at intermediate levels of intensity. Although a diversity of
environmental factors is manifest at any time and place, only one or a few of them tend to be dominant as
stressors. It is useful to distinguish between stressors that occur as severe events (disturbances) and those
268
that are chronic in their exposure, and to aggregate the kinds of stressors into categories (while noting
some degree of overlap among them).
Key words:
environmental stress, stressors, chronic stress, acute stress, anthropogenic stress, disturbance,
resistance, resilience, ecological integrity
Аннотация:
Режимы экологического стресса чрезвычайно сложный. Конкретные стрессоры
существуют в пределах континуума интенсивности факторов окружающей среды. Эти факторы
взаимодействуют друг с другом, и их пагубное воздействие на организмы проявляется только при
относительно высокой или низкой интенсивности воздействия – на самом деле, многие из них
полезны при промежуточных уровнях интенсивности. Хотя разнообразие факторов окружающей
среды проявляется в любое время и в любом месте, только один или несколько из них, как
правило, являются доминирующими факторами стресса. Полезно проводить различие между
стрессорами, которые проявляются как серьезные события или нарушения, и теми, которые
являются хроническими по своему воздействию, и объединяют виды стрессоров по категориям;
отмечая при этом некоторую степень совпадения между ними.
Ключевые слова:
экологический стресс, стрессоры, хронический стресс, острый стресс,
антропогенный стресс, нарушение, прочность, устойчивость, экологическая целостность
Ecology may be simply defined as the study of the relationships of organisms and their
environment. Within that context, the study of environmental influences or factors that affect organisms
and ecosystems is a core subject matter. Effects of environmental influences may be exerted at any level
of ecology: on individual organisms, populations, communities, echoscopes – landscapes or seascapes,
and, ultimately, the biosphere in its entirety. There are also influences on the functions of ecosystems,
such as productivity and nutrient cycling. At any particular time or place, the relative importance of those
influences can be beneficial, damaging, or inconsequential.
The study of environmental factors is an important aspect of ecology because it helps ecologists
to better understand the influences that affect, and perhaps even control, the structural and functional
attributes of ecosystems and their components. This understanding is of theoretical interest and is also
important to the application of ecological knowledge to the resolution of environmental problems.
Environmental factors exist as complex regimes of intensities of exposure, which vary on a
continuous scale as well as over space and time and also interact with each other. Within the continua of
intensity of environmental factors, the range of stressors is marked by a manifestation of detrimental
effects on organisms or ecosystem processes at relatively high or low strengths of exposure—in fact,
many factors are beneficial at intermediate levels. Although a great diversity of environmental factors are
manifest at any time and place, only one or a few tend to be dominant as stressors.
Stressors
of natural origin have always been part of the environmental context of organisms and
ecosystems. Increasingly, however, anthropogenic stressors, those associated with human activities, are
exerting an important influence. In fact,
anthropogenic stressors
are now more pronounced than natural
influences over vast tracts of ‗working‘ landscapes and seascapes that are being used to serve human
economies, such as in agricultural and urbanized areas.
As such, environmental stressors are influences that limit the performance of organisms or of
their characteristics at aggregate levels, such as those of a population or community. In the sense meant
here, ‗performance‘ of an individual is related to such attributes as its productivity and reproductive
fitness relative to its genetic potential. Almost always, the realized performance of an individual is less
than would be possible under optimal environmental conditions. Depending on the intensity of a stressor
regime, the growth and fitness of organisms may be diminished or even be made nonviable. Because
individuals may exhibit genetically based differences in their tolerance of stressors, this aspect of the
environmental regime has an influence on the evolutionary dynamics of populations and species.
Environmental stressors
also affect ecosystems at the larger scales of populations, communities,
and echoscopes. In these cases, ‗performance‘ may be indicated either by functional or structural
attributes of the system. Indicators of function would include the aggregate rates of productivity or
nutrient cycling performed by many individuals compared with what is possible under optimal
environmental conditions. Again, depending on the intensity of a stressor regime, the values of functions
or structural attributes may be diminished or even be made nonviable compared with what occurs under
optimal environmental conditions.
In any circumstance – meaning at a particular time and place – there is a complex regime of
interacting environmental stressors. For certain stressors, referred to as ‗disturbances‘, the exposure is
intense but short lived. For other stressors, there is a chronic exposure that does not rapidly change over
time.
269
The study of environmental stressors began with research into environmental factors, such as the
pioneering work of Justus von Liebig noted in the Introduction section.
Essentially, a
stressor
is an environmental factor that is available in too limited an amount to
satisfy the biological demand, or that occurs in such a great exposure that toxicity or other kinds of
damage are caused. Among the earliest researchers of environmental stressors were plant physiologists
who were interested in regimes of environmental conditions – such as nutrient and water availability, that
would optimize the productivity of crops. Later on, ecologists and toxicologists studied the poisonous
effects of industrial chemicals released into the environment, including gases such as sulphur dioxide and
ozone as well as metals and pesticides. In the 1960s, other ecologists began to examine how
environmental stressors have system-level effects, such as on the structural and functional attributes of
ecosystems. Examples of structural attributes that were being examined in earlier research on
environmental stressors included the composition and species richness of communities, spatial
distributions of the standing crops of biomass and nutrients, and trophic structure, while functional
attributes included nutrient cycling, productivity, and behavioral and trophic interactions among species.
Pioneers in these system-level studies include Gary W. Barrett (b. 1940), Fakhri A.Bazzaz (1933-
2008), J.Philip Grime (b. 1935), Eugene P. Odum (1913-2002), and David Schindler (b. 1940).
To varying degrees, organisms and higher-level ecological attributes, such as populations and
communities have a degree of tolerance to exposure to stressors. The suite of tolerances is an important
aspect of the niche of a species within its ecological community.
However, when an exposure becomes greater than the limit of tolerance, a response will occur.
This conceptual relationship is sometimes called the SER model – i.e.,
S
tress–
E
xposure–
R
esponse. It
describes how and to what degree biological and ecological changes will occur when the capacity of a
system to endure stressors is exceeded.
Stressors
that affect organisms and ecosystems are associated with various kinds of
environmental factors, such as: regimes of temperature, moisture, or nutrients, or of space, that are
insufficient to allow for growth rates that are as high as are genetically possible, as well as difficulties
associated with too intense an exposure to those same factors constraints associated with biological
interactions such as competition, disease, and predation short-lived events of disturbance – episodes of
mass destruction, as may be caused by a windstorm or by a clear-cut of a stand of forest.
The various kinds of
environmental stressors
are examined in more detail in the Kinds of
Environmental Stressors section.
Environmental stressors typically affect different species in a variety of ways. When a stressor regime
changes markedly, some species within a community will suffer damage while other species may realize
an ecological benefit. Consider, for example, a wildfire that affects a mature stand of jack pine – Pinus
banksiana, in an area of boreal forest of North America. Many individual trees are killed by the heat of
scorching or by combustion, which results in acute habitat changes that are detrimental to local
populations of most plant and animal species of the pre-fire mature forest. Nevertheless, the aftermath
conditions of the disturbance provide other species with suitable early-successional habitat, such as the
perennial herbaceous plant called fireweed – Epilobium angustifolium. These species increase greatly in
abundance after a wildfire and are prominent in the post disturbance recovery of the ecosystem.
Moreover, although most of the mature pine trees are killed by the wildfire, there may be a benefit to their
larger-scale meta-population, or regional population. This occurs because a severe wildfire combusts
much of the organic layer of an affected mature forest, which helps to prepare a mineral seedbed of the
kind needed for regeneration of jack pine. This can allow a cohort – even-aged population, of seedlings to
establish and then to grow, eventually producing another mature stand. Therefore, over the longer term,
occasional disturbances by wildfire may be necessary for jack pine and its stands to survive and grow on
the boreal landscape. In fact, wildfire as an environmental stressor must have played a role in the
evolutionary history that resulted in jack pine being relatively tolerant, at the population level, of this kind
of natural disturbance.
The intensity of environmental stressors may be exerted in various ways. For instance, chronic
stressors have a relatively continuous presence, and so they exercise their pressure over an extended
period of time. The characteristics of soil – such as its mineralogy and contents of water and nutrients, for
example, have a relatively uninterrupted influence on the productivity of plants within an ecological
community, even though soil factors do vary over space and time. This is also the case for many factors
related to climate, such as temperature and moisture availability. Chronic stressors, such as those that
occur in the desert or tundra, have a large influence on ecosystems, and if their intensity is severe they
may restrict development to a simple condition and low level of biodiversity.
Other stressors have an acute rather than a chronic influence. This effect, referred to as a
disturbance, is a short-lived event of destruction that affects dominant organisms in a community or over
270
a larger area such as a landscape. Examples of disturbances include wildfires, a hurricane or tornado,
flooding, and irruptive biological agents such as a disease epidemic or an infestation of defoliating
insects. A disturbance is followed by succession, which is a period of community-level recovery.
Conclusion: Our natural environment makes human life possible, and our cultural environment
helps define who we are. It is therefore essential that our population and economic growth are
environmentally sustainable. The most positive outlook for our environment is one in which we get the
balance right between:
continuing to support and implement effective policies, programs and resources
, for
example,
community engagement and volunteering programs,
IMOS,
Australia‘s Biodiversity Conservation Strategy 2010-2030,
the Great Barrier Reef Science Strategy,
the Reef 2050 Sustainability Plan,
NESP,
the Terrestrial Ecosystem Research Network,
the Australian Heritage Strategy,
the National Reserve System,
the National Representative System of Marine Protected Areas,
Indigenous Protected Area programs
further developing, testing and, as appropriate, implementing innovative approaches and
initiatives that are currently being developed
, for example, policies, technologies and management that
are decoupling the economy from environmental harm, environmental-economic accounting and
valuation, initiatives to reduce plastic pollution in coastal and marine environments, initiatives to reduce
air pollutants in urban areas
developing and implementing new policies, processes, programs and tools in the medium to
longer term, including the further integration of policies and management approaches across
jurisdictions and sectors
, for example, green or blue economy approaches, development of a
sophisticated impact investment market, regulatory reform to provide for rapid response to new
incursions of potentially harmful invasive species and disease.
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