1,194 research outputs found
The fundamental cycle of concept construction underlying various theoretical frameworks
In this paper, the development of mathematical concepts over time is considered. Particular reference is given to the shifting of attention from step-by-step procedures that are performed in time, to symbolism that can be manipulated as mental entities on paper and in the mind. The development is analysed using different theoretical perspectives, including the SOLO model and various theories of concept construction to reveal a fundamental cycle underlying the building of concepts that features widely in different ways of thinking that occurs throughout mathematical learning
Control of ornithine decarboxylase activity in α -difluoromethylornithine-resistant L1210 cells by polyamines and synthetic analogues
The regulation of ornithine decarboxylase (ODC) activity by the polyamine derivatives N1,N8-bis(ethyl)-spermidine and N1,N12-bis(ethyl)spermine was studied using a line of L1210 cells resistant to α -difluoromethylornithine (D-R cells), which contain very high levels of ODC, and a synthetic mRNA prepared from a plasmid containing an insert corresponding to ODC mRNA adjacent to an SP6 RNA polymerase promoter. Studies in which ODC protein was labeled in the D-R cells by exposure to [35S]methionine indicated that the polyamine derivatives and their physiological counterparts led to an increased rate of degradation of ODC and to a rapid reduction in ODC synthesis without affecting the content of ODC mRNA. Direct evidence that the polyamine derivatives act by inhibiting the translation of the ODC mRNA was obtained by studying their effects on the translation of ODC mRNA in reticulocyte lysates. This translation was strongly inhibited by the addition of N1,N8-bis(ethyl)spermidine, spermidine, N1,N12-bis(ethyl)spermine, or spermine but was not affected much by putrescine. The inhibition of the translation of ODC mRNA by either of the bis(ethyl) polyamine derivatives occurred at concentrations which stimulated total protein synthesis showing the selectivity of the reduction in ODC. The effects of polyamine derivatives and polyamines on translation of the plasmid-derived ODC mRNA were identical with those found with the D-R L1210 cell mRNA. This synthetic ODC mRNA lacks 261 bases of the 5'-leader sequences and 200 bases plus the poly(A) section from the 3'-nontranslated sequence. Therefore, these regions appear not to influence sensitivity of the ODC mRNA to inhibition of translation by polyamine derivatives
Creation of macroscopic quantum superposition states by a measurement
We propose a novel protocol for the creation of macroscopic quantum
superposition (MQS) states based on a measurement of a non-monotonous function
of a quantum collective variable. The main advantage of this protocol is that
it does not require switching on and off nonlinear interactions in the system.
We predict this protocol to allow the creation of multiatom MQS by measuring
the number of atoms coherently outcoupled from a two-component (spinor)
Bose-Einstein condensate.Comment: 4 pages (revtex4), 2 figure
Ultracold atoms in radio-frequency-dressed potentials beyond the rotating wave approximation
We study dressed Bose-Einstein condensates in an atom chip radio-frequency
trap. We show that in this system sufficiently strong dressing can be achieved
to cause the widely used rotating wave approximation (RWA) to break down. We
present a full calculation of the atom - field coupling which shows that the
non-RWA contributions quantitatively alter the shape of the emerging dressed
adiabatic potentials. The non-RWA contributions furthermore lead to additional
allowed transitions between dressed levels. We use RF spectroscopy of
Bose-Einstein condensates trapped in the dressed state potentials to directly
observe the transition from the RWA to the beyond-RWA regime.Comment: 6 pages, 4 figure
Photodetachment study of the 1s3s4s ^4S resonance in He^-
A Feshbach resonance associated with the 1s3s4s ^{4}S state of He^{-} has
been observed in the He(1s2s ^{3}S) + e^- (\epsilon s) partial photodetachment
cross section. The residual He(1s2s ^{3}S) atoms were resonantly ionized and
the resulting He^+ ions were detected in the presence of a small background. A
collinear laser-ion beam apparatus was used to attain both high resolution and
sensitivity. We measured a resonance energy E_r = 2.959 255(7) eV and a width
\Gamma = 0.19(3) meV, in agreement with a recent calculation.Comment: LaTeX article, 4 pages, 3 figures, 21 reference
Effects of diamines on ornithine decarboxylase activity in control and virally transformed mouse fibroblasts
Uncorking the potential of wine language for young wine tourists
Effective communication with consumers underpins growth in wine knowledge that, in turn, contributes to growth in wine consumption. Indeed, tasting notes may enhance consumers’ experiences of wine. Yet wine language is full of fuzzy concepts. In this chapter, we consider the language used to talk about wine, specifically the humanlike features of wine (e.g., wine is described as honest, sexy, shy, or brooding). We demonstrate that metaphoric language is integral to the experience of wine and influences consumer behaviour. We discuss practical implications for the cellar door experience, and for effective and ethical wine communication. We conclude that metaphoric language is a pedagogical and cultural platform for engaging younger wine tourists in the cellar door experience, which is a significant revenue source for micro, small, and medium wineries
Feynman's path integral and mutually unbiased bases
Our previous work on quantum mechanics in Hilbert spaces of finite dimensions
N is applied to elucidate the deep meaning of Feynman's path integral pointed
out by G. Svetlichny. He speculated that the secret of the Feynman path
integral may lie in the property of mutual unbiasedness of temporally proximal
bases. We confirm the corresponding property of the short-time propagator by
using a specially devised N x N -approximation of quantum mechanics in L^2(R)
applied to our finite-dimensional analogue of a free quantum particle.Comment: 12 pages, submitted to Journal of Physics A: Math. Theor., minor
correction
Induction of spermidine/spermine N1-acetyltransferase activity in Chinese-hamster ovary cells by N1N11-bis(ethyl)norspermine (corrected) and related compounds
Structure and regulation of mammalian S-adenosylmethionine decarboxylase
In order to understand the structure and regulation of S-adenosylmethionine decarboxylase, cDNA clones encoding this enzyme have been isolated from rat prostate and human fibroblast cDNA libraries. The authenticity of the cDNAs was verified by: (a) transfecting the Chinese hamster ovary cells with the human cDNA in the pcD vector which resulted in a transient 10-20-fold increase in S-adenosylmethionine decarboxylase activity in recipient cells; and (b) translating the mRNA formed by transcription of the cDNA insert in a reticulocyte lysate and recording an increase in S-adenosylmethionine decarboxylase activity. The amino acid sequences deduced from the cDNAs indicate that the human proenzyme for this protein contains 334 amino acids and has a molecular weight of 38,331 whereas the rat proenzyme contains 333 amino acid residues. The human and rat enzymes are very similar having only 11 amino acid differences and the cDNAs are also closely related showing over 90% homology in the 1617-nucleotide overlap which was sequenced. A further indication of the highly conserved nature of mammalian S-adenosylmethionine decarboxylases is that the amino acid sequences deduced from the human and the rat cDNAs contained peptide sequences identical to those previously reported for the purified bovine enzyme. In vitro transcription/translation experiments showed that the proenzyme is converted to two polypeptides of molecular weights about 32,000 and 6,000 in a processing reaction which generates the prosthetic pyruvate group and that the final enzyme contains both polypeptides. Two forms of S-adenosylmethionine decarboxylase mRNA (2.1 and about 3.4-3.6 kilobases) are present in human and rodent tissues and may originate from the utilization of two different polyadenylation signals. Southern blots of rat genomic DNA indicated that the S-adenosylmethionine decarboxylase gene belongs to a multigene family. Depletion of cellular polyamines by inhibitors or ornithine decarboxylase or the aminopropyltransferases led to an increase in the content of S-adenosylmethionine decarboxylase protein and mRNA, but the elevation in the mRNA was not sufficient to account for all of the change in the enzyme level, particularly in cells in which spermine was depleted
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