158 research outputs found
Role of humic substances in agriculture and variability of their content in freshwater lake sapropel
ArticleThe term ‘humic substances’ (HS) refers to a general category of naturally occurring,
biogenic, heterogeneous organic substances. They create the most widespread natural organic
matter found in sediments, soils and waters. Organic carbon in soil (up to 70%) and peat (up to
90%) usually occurs in the form of HS. HS influence the formation process of fossil fuels, as well
as they are involved in the plant nutrition process, have an influence on availability and toxicity
of metallic and other elements. Furthermore, HS play a significant role in the global carbon
geochemical cycle. Properties and application efficiency of humus depend on the source of HS.
Freshwater sapropel is a huge reservoir of HS with superior biological activity, although their
total content is lower than in peat. The aim of this paper, firstly, was to present the information
about the options of HS in agriculture and their main effects on plant growth. Secondly,
determination and characterization of HS content in freshwater lake sapropel was performed as
sapropel nowadays becomes a popular natural organic-mineral fertilizer and soil conditioner.
Sapropel samples were derived from Lake Pilvelis, Lake Pilcines, Lake Vevers, Lake Liducis and
Lake Padelis situated in Eastern Latvia. Investigation of HS content in sapropel is significant for
the Baltic States and Northern Europe due to wide distribution and availability of sapropel in
freshwater bodies. That promotes a search for new ways of extraction methods and
bioeconomically effective utilization of this natural resource, obtainable in economically
significant amounts, with high opportunities of its use especially in agriculture. Contemporary
agriculture strongly desiderates in new products of high effectivity enhancing soil and crop
productivity and quality hand in hand with sustainable development and careful attitude to the
nature and surrounding environment, thus, one of the ways how it can be achieved is
understanding how, where and how much HS preparations can be applied
Money and Goldstone modes
Why is ``worthless'' fiat money generally accepted as payment for goods and
services? In equilibrium theory, the value of money is generally not
determined: the number of equations is one less than the number of unknowns, so
only relative prices are determined. In the language of mathematics, the
equations are ``homogeneous of order one''. Using the language of physics, this
represents a continuous ``Goldstone'' symmetry. However, the continuous
symmetry is often broken by the dynamics of the system, thus fixing the value
of the otherwise undetermined variable. In economics, the value of money is a
strategic variable which each agent must determine at each transaction by
estimating the effect of future interactions with other agents. This idea is
illustrated by a simple network model of monopolistic vendors and buyers, with
bounded rationality. We submit that dynamical, spontaneous symmetry breaking is
the fundamental principle for fixing the value of money. Perhaps the continuous
symmetry representing the lack of restoring force is also the fundamental
reason for large fluctuations in stock markets.Comment: 7 pages, 3 figure
Synthesizing Rulesets for Programmable Robotic Self-Assembly: A Case Study using Floating Miniaturized Robots
A comparative study of the properties of industrially produced humic substances
Humic substances (HSs) are produced industrially in large quantities from low rank
coal, weathered coal, peat, also from soils, composts and other sources. Considering that the
applications of industrially produced HSs also include food, pharmaceutical applications and
environmental technologies, it is important to evaluate their composition and quality and to
identify their sources. The aim of the present study is to compare the properties of industrially
produced HS samples. HSs were characterised using spectroscopic and other methods. For the
identification of origin of HSs, different methods can be used, such as elemental analysis and
ratios of light stable isotopes. The results of the study indicate that many industrially produced
HSs are of poor quality (low concentration of basic substance, admixture of undesirable
substances, pollutants, no quality indications). In this situation, rigorous quality control should
be implemented, providing detailed characteristics of the product. The composition of materials
suggested for agricultural applications has not been analysed much. Most of the studied materials
were designated as HAs, followed by fulvic acids (FAs) and HSs. However, an analysis of the
humic matter types indicates that the majority of substances offered on the market are in fact
mixtures of HAs and FAs; so, it would be more appropriate to designate them as HSs or their
salts. This study identifies the main quality problems of industrially produced humic substances:
1) lack of strict quality indicators, 2) absence of indication of source materials/origins of HSs
Long range order and two-fluid behavior in heavy electron materials
The heavy electron Kondo liquid is an emergent state of condensed matter that
displays universal behavior independent of material details. Properties of the
heavy electron liquid are best probed by NMR Knight shift measurements, which
provide a direct measure of the behavior of the heavy electron liquid that
emerges below the Kondo lattice coherence temperature as the lattice of local
moments hybridizes with the background conduction electrons. Because the
transfer of spectral weight between the localized and itinerant electronic
degrees of freedom is gradual, the Kondo liquid typically coexists with the
local moment component until the material orders at low temperatures. The
two-fluid formula captures this behavior in a broad range of materials in the
paramagnetic state. In order to investigate two-fluid behavior and the onset
and physical origin of different long range ordered ground states in heavy
electron materials, we have extended Knight shift measurements to
URuSi, CeIrIn and CeRhIn. In CeRhIn we find that the
antiferromagnetic order is preceded by a relocalization of the Kondo liquid,
providing independent evidence for a local moment origin of antiferromagnetism.
In URuSi the hidden order is shown to emerge directly from the Kondo
liquid and so is not associated with local moment physics. Our results imply
that the nature of the ground state is strongly coupled with the hybridization
in the Kondo lattice in agreement with phase diagram proposed by Yang and
Pines.Comment: 9 pages, 13 figure
Magnetic structure and Kondo lattice behavior in CeVGe: an NMR and neutron scattering study
We present nuclear magnetic resonance (NMR), neutron diffraction,
magnetization, and transport measurements on a single crystal and powder of
CeVGe. This material exhibits heavy fermion behavior at low temperature,
accompanied by antiferromagnetic (AFM) order below 5.8 K. We find that the
magnetic structure is incommensurate with AFM helical structure, characterized
by a magnetic modulated propagation vector of with in-plane
moments rotating around the -axis. The NMR Knight shift and spin-lattice
relaxation rate reveal a coherence temperature K, and the presence
of significant antiferromagnetic fluctuations reminiscent of the archetypical
heavy fermion compound CeRhIn. We further identify a metamagnetic
transition above T for magnetic fields perpendicular to . We
speculate that the magnetic structure in this field-induced phase consists of a
superposition with both ferromagnetic and antiferromagnetic components, which
is consistent with the NMR spectrum in this region of the phase diagram. Our
results thus indicate that CeVGe is a hexagonal structure analog to
tetragonal CeRhIn.Comment: 13 pages, 11 figure
Excitation transfer between the rubidium 5 2 D fine-structure levels in collisions with ground-state rubidium atoms: Experiment and theory
We report a study of fine-structure mixing Rb(5 2 D 5/2 )→Rb(5 2 D 3/2 ) in collisions with ground-state Rb atoms. In the experiment, two-photon cw laser excitation was applied to the Rb vapor cell. The measured cross section for the process was (5.8Ϯ1.9)ϫ10 Ϫ14 cm 2 . Theoretical calculations using nonadiabatic collision theory gave a value of 3.4ϫ10 Ϫ14 cm 2
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