Temporal Structures in Positron Spectra and Charge-Sign Effects in Galactic Cosmic Rays

We present the precision measurements of 11 years of daily cosmic positron fluxes in the rigidity range from 1.00 to 41.9 GV based on 3.4×10^{6} positrons collected with the Alpha Magnetic Spectrometer (AMS) aboard the International Space Station. The positron fluxes show distinctly different time variations from the electron fluxes at short and long timescales. A hysteresis between the electron fluxes and the positron fluxes is observed with a significance greater than 5σ at rigidities below 8.5 GV. On the contrary, the positron fluxes and the proton fluxes show similar time variation. Remarkably, we found that positron fluxes are modulated more than proton fluxes with a significance greater than 5σ for rigidities below 7 GV. These continuous daily positron fluxes, together with AMS daily electron, proton, and helium fluxes over an 11-year solar cycle, provide unique input to the understanding of both the charge-sign and mass dependencies of cosmic rays in the heliosphere.

Properties of Cosmic-Ray Sulfur and Determination of the Composition of Primary Cosmic-Ray Carbon, Neon, Magnesium, and Sulfur: Ten-Year Results from the Alpha Magnetic Spectrometer

We report the properties of primary cosmic-ray sulfur (S) in the rigidity range 2.15 GV to 3.0 TV based on 0.38×10^{6} sulfur nuclei collected by the Alpha Magnetic Spectrometer experiment (AMS). We observed that above 90 GV the rigidity dependence of the S flux is identical to the rigidity dependence of Ne-Mg-Si fluxes, which is different from the rigidity dependence of the He-C-O-Fe fluxes. We found that, similar to N, Na, and Al cosmic rays, over the entire rigidity range, the traditional primary cosmic rays S, Ne, Mg, and C all have sizeable secondary components, and the S, Ne, and Mg fluxes are well described by the weighted sum of the primary silicon flux and the secondary fluorine flux, and the C flux is well described by the weighted sum of the primary oxygen flux and the secondary boron flux. The primary and secondary contributions of the traditional primary cosmic-ray fluxes of C, Ne, Mg, and S (even Z elements) are distinctly different from the primary and secondary contributions of the N, Na, and Al (odd Z elements) fluxes. The abundance ratio at the source for S/Si is 0.167±0.006, for Ne/Si is 0.833±0.025, for Mg/Si is 0.994±0.029, and for C/O is 0.836±0.025. These values are determined independent of cosmic-ray propagation.

Temporal Structures in Electron Spectra and Charge Sign Effects in Galactic Cosmic Rays

We present the precision measurements of 11 years of daily cosmic electron fluxes in the rigidity interval from 1.00 to 41.9 GV based on 2.0×10^{8} electrons collected with the Alpha Magnetic Spectrometer (AMS) aboard the International Space Station. The electron fluxes exhibit variations on multiple timescales. Recurrent electron flux variations with periods of 27 days, 13.5 days, and 9 days are observed. We find that the electron fluxes show distinctly different time variations from the proton fluxes. Remarkably, a hysteresis between the electron flux and the proton flux is observed with a significance of greater than 6σ at rigidities below 8.5 GV. Furthermore, significant structures in the electron-proton hysteresis are observed corresponding to sharp structures in both fluxes. This continuous daily electron data provide unique input to the understanding of the charge sign dependence of cosmic rays over an 11-year solar cycle.

Properties of Daily Helium Fluxes

We present the precision measurement of 2824 daily helium fluxes in cosmic rays from May 20, 2011 to October 29, 2019 in the rigidity interval from 1.71 to 100 GV based on 7.6×10^{8} helium nuclei collected with the Alpha Magnetic Spectrometer (AMS) aboard the International Space Station. The helium flux and the helium to proton flux ratio exhibit variations on multiple timescales. In nearly all the time intervals from 2014 to 2018, we observed recurrent helium flux variations with a period of 27 days. Shorter periods of 9 days and 13.5 days are observed in 2016. The strength of all three periodicities changes with time and rigidity. In the entire time period, we found that below ∼7  GV the helium flux exhibits larger time variations than the proton flux, and above ∼7  GV the helium to proton flux ratio is time independent. Remarkably, below 2.4 GV a hysteresis between the helium to proton flux ratio and the helium flux was observed at greater than the 7σ level. This shows that at low rigidity the modulation of the helium to proton flux ratio is different before and after the solar maximum in 2014.

Periodicities in the Daily Proton Fluxes from 2011 to 2019 Measured by the Alpha Magnetic Spectrometer on the International Space Station from 1 to 100 GV

We present the precision measurement of the daily proton fluxes in cosmic rays from May 20, 2011 to October 29, 2019 (a total of 2824 days or 114 Bartels rotations) in the rigidity interval from 1 to 100 GV based on 5.5×10^{9} protons collected with the Alpha Magnetic Spectrometer aboard the International Space Station. The proton fluxes exhibit variations on multiple timescales. From 2014 to 2018, we observed recurrent flux variations with a period of 27 days. Shorter periods of 9 days and 13.5 days are observed in 2016. The strength of all three periodicities changes with time and rigidity. The rigidity dependence of the 27-day periodicity is different from the rigidity dependences of 9-day and 13.5-day periods. Unexpectedly, the strength of 9-day and 13.5-day periodicities increases with increasing rigidities up to ∼10  GV and ∼20  GV, respectively. Then the strength of the periodicities decreases with increasing rigidity up to 100 GV.

Erratum: Properties of a New Group of Cosmic Nuclei: Results from the Alpha Magnetic Spectrometer on Sodium, Aluminum, and Nitrogen [Phys. Rev. Lett. 127, 021101 (2021)]

This corrects the article DOI: 10.1103/PhysRevLett.127.021101.

Properties of a New Group of Cosmic Nuclei: Results from the Alpha Magnetic Spectrometer on Sodium, Aluminum, and Nitrogen

We report the properties of sodium (Na) and aluminum (Al) cosmic rays in the rigidity range 2.15 GV to 3.0 TV based on 0.46 million sodium and 0.51 million aluminum nuclei collected by the Alpha Magnetic Spectrometer experiment on the International Space Station. We found that Na and Al, together with nitrogen (N), belong to a distinct cosmic ray group. In this group, we observe that, similar to the N flux, both the Na flux and Al flux are well described by the sums of a primary cosmic ray component (proportional to the silicon flux) and a secondary cosmic ray component (proportional to the fluorine flux). The fraction of the primary component increases with rigidity for the N, Na, and Al fluxes and becomes dominant at the highest rigidities. The Na/Si and Al/Si abundance ratios at the source, 0.036±0.003 for Na/Si and 0.103±0.004 for Al/Si, are determined independent of cosmic ray propagation.

Properties of Heavy Secondary Fluorine Cosmic Rays: Results from the Alpha Magnetic Spectrometer

Precise knowledge of the charge and rigidity dependence of the secondary cosmic ray fluxes and the secondary-to-primary flux ratios is essential in the understanding of cosmic ray propagation. We report the properties of heavy secondary cosmic ray fluorine F in the rigidity R range 2.15 GV to 2.9 TV based on 0.29 million events collected by the Alpha Magnetic Spectrometer experiment on the International Space Station. The fluorine spectrum deviates from a single power law above 200 GV. The heavier secondary-to-primary F/Si flux ratio rigidity dependence is distinctly different from the lighter B/O (or B/C) rigidity dependence. In particular, above 10 GV, the F/Si/B/O ratio can be described by a power law R^{δ} with δ=0.052±0.007. This shows that the propagation properties of heavy cosmic rays, from F to Si, are different from those of light cosmic rays, from He to O, and that the secondary cosmic rays have two classes.

Properties of Iron Primary Cosmic Rays: Results from the Alpha Magnetic Spectrometer

We report the observation of new properties of primary iron (Fe) cosmic rays in the rigidity range 2.65 GV to 3.0 TV with 0.62×10^{6} iron nuclei collected by the Alpha Magnetic Spectrometer experiment on the International Space Station. Above 80.5 GV the rigidity dependence of the cosmic ray Fe flux is identical to the rigidity dependence of the primary cosmic ray He, C, and O fluxes, with the Fe/O flux ratio being constant at 0.155±0.006. This shows that unexpectedly Fe and He, C, and O belong to the same class of primary cosmic rays which is different from the primary cosmic rays Ne, Mg, and Si class.

Properties of Neon, Magnesium, and Silicon Primary Cosmic Rays Results from the Alpha Magnetic Spectrometer

We report the observation of new properties of primary cosmic rays, neon (Ne), magnesium (Mg), and silicon (Si), measured in the rigidity range 2.15 GV to 3.0 TV with 1.8×10^{6}  Ne, 2.2×10^{6}  Mg, and 1.6×10^{6}  Si nuclei collected by the Alpha Magnetic Spectrometer experiment on the International Space Station. The Ne and Mg spectra have identical rigidity dependence above 3.65 GV. The three spectra have identical rigidity dependence above 86.5 GV, deviate from a single power law above 200 GV, and harden in an identical way. Unexpectedly, above 86.5 GV the rigidity dependence of primary cosmic rays Ne, Mg, and Si spectra is different from the rigidity dependence of primary cosmic rays He, C, and O. This shows that the Ne, Mg, and Si and He, C, and O are two different classes of primary cosmic rays.

Properties of Cosmic Helium Isotopes Measured by the Alpha Magnetic Spectrometer

Precision measurements by the Alpha Magnetic Spectrometer (AMS) on the International Space Station of ^{3}He and ^{4}He fluxes are presented. The measurements are based on 100 million ^{4}He nuclei in the rigidity range from 2.1 to 21 GV and 18 million ^{3}He from 1.9 to 15 GV collected from May 2011 to November 2017. We observed that the ^{3}He and ^{4}He fluxes exhibit nearly identical variations with time. The relative magnitude of the variations decreases with increasing rigidity. The rigidity dependence of the ^{3}He/^{4}He flux ratio is measured for the first time. Below 4 GV, the ^{3}He/^{4}He flux ratio was found to have a significant long-term time dependence. Above 4 GV, the ^{3}He/^{4}He flux ratio was found to be time independent, and its rigidity dependence is well described by a single power law ∝R^{Δ} with Δ=-0.294±0.004. Unexpectedly, this value is in agreement with the B/O and B/C spectral indices at high energies.

Towards Understanding the Origin of Cosmic-Ray Electrons

Precision results on cosmic-ray electrons are presented in the energy range from 0.5 GeV to 1.4 TeV based on 28.1×10^{6} electrons collected by the Alpha Magnetic Spectrometer on the International Space Station. In the entire energy range the electron and positron spectra have distinctly different magnitudes and energy dependences. The electron flux exhibits a significant excess starting from 42.1_{-5.2}^{+5.4}  GeV compared to the lower energy trends, but the nature of this excess is different from the positron flux excess above 25.2±1.8  GeV. Contrary to the positron flux, which has an exponential energy cutoff of 810_{-180}^{+310}  GeV, at the 5σ level the electron flux does not have an energy cutoff below 1.9 TeV. In the entire energy range the electron flux is well described by the sum of two power law components. The different behavior of the cosmic-ray electrons and positrons measured by the Alpha Magnetic Spectrometer is clear evidence that most high energy electrons originate from different sources than high energy positrons.

Towards Understanding the Origin of Cosmic-Ray Positrons

Precision measurements of cosmic ray positrons are presented up to 1 TeV based on 1.9 million positrons collected by the Alpha Magnetic Spectrometer on the International Space Station. The positron flux exhibits complex energy dependence. Its distinctive properties are (a) a significant excess starting from 25.2±1.8  GeV compared to the lower-energy, power-law trend, (b) a sharp dropoff above 284_{-64}^{+91}  GeV, (c) in the entire energy range the positron flux is well described by the sum of a term associated with the positrons produced in the collision of cosmic rays, which dominates at low energies, and a new source term of positrons, which dominates at high energies, and (d) a finite energy cutoff of the source term of E_{s}=810_{-180}^{+310}  GeV is established with a significance of more than 4σ. These experimental data on cosmic ray positrons show that, at high energies, they predominantly originate either from dark matter annihilation or from other astrophysical sources.

Novel RNA aptamers targeting gastrointestinal cancer biomarkers CEA, CA50 and CA72-4 with superior affinity and specificity

Gastric cancer is the third most common cause of death from cancer in the world and it remains difficult to cure in Western countries, primarily because most patients present with advanced disease. Currently, CEA, CA50 and CA72-4 are commonly used as tumor markers for gastric cancer by immunoassays. However, the drawback and conundrum of immunoassay are the unceasing problem in standardization of quality of antibodies and time/effort for the intensive production. Therefore, there is an urgent need for the development of a standardized assay to detect gastric cancer at the early stage. Aptamers are DNA or RNA oligonucleotides with structural domain which recognize ligands such as proteins with superior affinity and specificity when compared to antibodies. In this study, SELEX (Systematic Evolution of Ligands by Exponential enrichment) technique was adopted to screen a random 30mer RNA library for aptamers targeting CEA, CA50 and CA72-4 respectively. Combined with high-throughput sequencing, we identified 6 aptamers which specifically target for these three biomarkers of gastrointestinal cancer. Intriguingly, the predicted secondary structures of RNA aptamers from each antigen showed significant structural similarity, suggesting the structural recognition between the aptamers and the antigens. Moreover, we determined the dissociation constants of all the aptamers to their corresponding antigens by fluorescence spectroscopy, which further demonstrated high affinities between the aptamers and the antigens. In addition, immunostaining of gastric adenocarcinoma cell line AGS using CEA Aptamer probe showed positive fluorescent signal which proves the potential of the aptamer as a detection tool for gastric cancer. Furthermore, substantially decreased cell viability and growth were observed when human colorectal cell line LS-174T was transfected with each individual aptamers. Taking together, these novel RNA aptamers targeting gastrointestinal cancer biomarker CEA, CA50 and CA72-4 will aid further development and standardization of clinical diagnostic method with better sensitivity and specificity, and potentially future therapeutics development of gastric cancer.

Observation of Complex Time Structures in the Cosmic-Ray Electron and Positron Fluxes with the Alpha Magnetic Spectrometer on the International Space Station

We present high-statistics, precision measurements of the detailed time and energy dependence of the primary cosmic-ray electron flux and positron flux over 79 Bartels rotations from May 2011 to May 2017 in the energy range from 1 to 50 GeV. For the first time, the charge-sign dependent modulation during solar maximum has been investigated in detail by leptons alone. Based on 23.5×10^{6} events, we report the observation of short-term structures on the timescale of months coincident in both the electron flux and the positron flux. These structures are not visible in the e^{+}/e^{-} flux ratio. The precision measurements across the solar polarity reversal show that the ratio exhibits a smooth transition over 830±30 days from one value to another. The midpoint of the transition shows an energy dependent delay relative to the reversal and changes by 260±30 days from 1 to 6 GeV.

Precision Measurement of Cosmic-Ray Nitrogen and its Primary and Secondary Components with the Alpha Magnetic Spectrometer on the International Space Station

A precision measurement of the nitrogen flux with rigidity (momentum per unit charge) from 2.2 GV to 3.3 TV based on 2.2×10^{6} events is presented. The detailed rigidity dependence of the nitrogen flux spectral index is presented for the first time. The spectral index rapidly hardens at high rigidities and becomes identical to the spectral indices of primary He, C, and O cosmic rays above ∼700  GV. We observed that the nitrogen flux Φ_{N} can be presented as the sum of its primary component Φ_{N}^{P} and secondary component Φ_{N}^{S}, Φ_{N}=Φ_{N}^{P}+Φ_{N}^{S}, and we found Φ_{N} is well described by the weighted sum of the oxygen flux Φ_{O} (primary cosmic rays) and the boron flux Φ_{B} (secondary cosmic rays), with Φ_{N}^{P}=(0.090±0.002)×Φ_{O} and Φ_{N}^{S}=(0.62±0.02)×Φ_{B} over the entire rigidity range. This corresponds to a change of the contribution of the secondary cosmic ray component in the nitrogen flux from 70% at a few GV to <30% above 1 TV.

Observation of Fine Time Structures in the Cosmic Proton and Helium Fluxes with the Alpha Magnetic Spectrometer on the International Space Station

We present the precision measurement from May 2011 to May 2017 (79 Bartels rotations) of the proton fluxes at rigidities from 1 to 60 GV and the helium fluxes from 1.9 to 60 GV based on a total of 1×10^{9} events collected with the Alpha Magnetic Spectrometer aboard the International Space Station. This measurement is in solar cycle 24, which has the solar maximum in April 2014. We observed that, below 40 GV, the proton flux and the helium flux show nearly identical fine structures in both time and relative amplitude. The amplitudes of the flux structures decrease with increasing rigidity and vanish above 40 GV. The amplitudes of the structures are reduced during the time period, which started one year after solar maximum, when the proton and helium fluxes steadily increase. Above ∼3  GV the p/He flux ratio is time independent. We observed that below ∼3  GV the ratio has a long-term decrease coinciding with the period during which the fluxes start to rise.

Observation of New Properties of Secondary Cosmic Rays Lithium, Beryllium, and Boron by the Alpha Magnetic Spectrometer on the International Space Station

We report on the observation of new properties of secondary cosmic rays Li, Be, and B measured in the rigidity (momentum per unit charge) range 1.9 GV to 3.3 TV with a total of 5.4×10^{6} nuclei collected by AMS during the first five years of operation aboard the International Space Station. The Li and B fluxes have an identical rigidity dependence above 7 GV and all three fluxes have an identical rigidity dependence above 30 GV with the Li/Be flux ratio of 2.0±0.1. The three fluxes deviate from a single power law above 200 GV in an identical way. This behavior of secondary cosmic rays has also been observed in the AMS measurement of primary cosmic rays He, C, and O but the rigidity dependences of primary cosmic rays and of secondary cosmic rays are distinctly different. In particular, above 200 GV, the secondary cosmic rays harden more than the primary cosmic rays.

Observation of the Identical Rigidity Dependence of He, C, and O Cosmic Rays at High Rigidities by the Alpha Magnetic Spectrometer on the International Space Station

We report the observation of new properties of primary cosmic rays He, C, and O measured in the rigidity (momentum/charge) range 2 GV to 3 TV with 90×10^{6} helium, 8.4×10^{6} carbon, and 7.0×10^{6} oxygen nuclei collected by the Alpha Magnetic Spectrometer (AMS) during the first five years of operation. Above 60 GV, these three spectra have identical rigidity dependence. They all deviate from a single power law above 200 GV and harden in an identical way.

Precision Measurement of the Boron to Carbon Flux Ratio in Cosmic Rays from 1.9 GV to 2.6 TV with the Alpha Magnetic Spectrometer on the International Space Station

Knowledge of the rigidity dependence of the boron to carbon flux ratio (B/C) is important in understanding the propagation of cosmic rays. The precise measurement of the B/C ratio from 1.9 GV to 2.6 TV, based on 2.3 million boron and 8.3 million carbon nuclei collected by AMS during the first 5 years of operation, is presented. The detailed variation with rigidity of the B/C spectral index is reported for the first time. The B/C ratio does not show any significant structures in contrast to many cosmic ray models that require such structures at high rigidities. Remarkably, above 65 GV, the B/C ratio is well described by a single power law R^{Δ} with index Δ=-0.333±0.014(fit)±0.005(syst), in good agreement with the Kolmogorov theory of turbulence which predicts Δ=-1/3 asymptotically.

Antiproton Flux, Antiproton-to-Proton Flux Ratio, and Properties of Elementary Particle Fluxes in Primary Cosmic Rays Measured with the Alpha Magnetic Spectrometer on the International Space Station

A precision measurement by AMS of the antiproton flux and the antiproton-to-proton flux ratio in primary cosmic rays in the absolute rigidity range from 1 to 450 GV is presented based on 3.49×10^{5} antiproton events and 2.42×10^{9} proton events. The fluxes and flux ratios of charged elementary particles in cosmic rays are also presented. In the absolute rigidity range ∼60 to ∼500  GV, the antiproton p[over ¯], proton p, and positron e^{+} fluxes are found to have nearly identical rigidity dependence and the electron e^{-} flux exhibits a different rigidity dependence. Below 60 GV, the (p[over ¯]/p), (p[over ¯]/e^{+}), and (p/e^{+}) flux ratios each reaches a maximum. From ∼60 to ∼500  GV, the (p[over ¯]/p), (p[over ¯]/e^{+}), and (p/e^{+}) flux ratios show no rigidity dependence. These are new observations of the properties of elementary particles in the cosmos.

Precision Measurement of the Helium Flux in Primary Cosmic Rays of Rigidities 1.9 GV to 3 TV with the Alpha Magnetic Spectrometer on the International Space Station

Knowledge of the precise rigidity dependence of the helium flux is important in understanding the origin, acceleration, and propagation of cosmic rays. A precise measurement of the helium flux in primary cosmic rays with rigidity (momentum/charge) from 1.9 GV to 3 TV based on 50 million events is presented and compared to the proton flux. The detailed variation with rigidity of the helium flux spectral index is presented for the first time. The spectral index progressively hardens at rigidities larger than 100 GV. The rigidity dependence of the helium flux spectral index is similar to that of the proton spectral index though the magnitudes are different. Remarkably, the spectral index of the proton to helium flux ratio increases with rigidity up to 45 GV and then becomes constant; the flux ratio above 45 GV is well described by a single power law.

Precision Measurement of the Proton Flux in Primary Cosmic Rays from Rigidity 1 GV to 1.8 TV with the Alpha Magnetic Spectrometer on the International Space Station

A precise measurement of the proton flux in primary cosmic rays with rigidity (momentum/charge) from 1 GV to 1.8 TV is presented based on 300 million events. Knowledge of the rigidity dependence of the proton flux is important in understanding the origin, acceleration, and propagation of cosmic rays. We present the detailed variation with rigidity of the flux spectral index for the first time. The spectral index progressively hardens at high rigidities.

Precision Measurement of the (e^{+}+e^{-}) Flux in Primary Cosmic Rays from 0.5 GeV to 1 TeV with the Alpha Magnetic Spectrometer on the International Space Station

We present a measurement of the cosmic ray (e^{+}+e^{-}) flux in the range 0.5 GeV to 1 TeV based on the analysis of 10.6 million (e^{+}+e^{-}) events collected by AMS. The statistics and the resolution of AMS provide a precision measurement of the flux. The flux is smooth and reveals new and distinct information. Above 30.2 GeV, the flux can be described by a single power law with a spectral index γ=-3.170±0.008(stat+syst)±0.008(energy scale).

Electron and positron fluxes in primary cosmic rays measured with the alpha magnetic spectrometer on the international space station

Precision measurements by the Alpha Magnetic Spectrometer on the International Space Station of the primary cosmic-ray electron flux in the range 0.5 to 700 GeV and the positron flux in the range 0.5 to 500 GeV are presented. The electron flux and the positron flux each require a description beyond a single power-law spectrum. Both the electron flux and the positron flux change their behavior at ∼30  GeV but the fluxes are significantly different in their magnitude and energy dependence. Between 20 and 200 GeV the positron spectral index is significantly harder than the electron spectral index. The determination of the differing behavior of the spectral indices versus energy is a new observation and provides important information on the origins of cosmic-ray electrons and positrons.

High statistics measurement of the positron fraction in primary cosmic rays of 0.5-500 GeV with the alpha magnetic spectrometer on the international space station

A precision measurement by AMS of the positron fraction in primary cosmic rays in the energy range from 0.5 to 500 GeV based on 10.9 million positron and electron events is presented. This measurement extends the energy range of our previous observation and increases its precision. The new results show, for the first time, that above ∼200  GeV the positron fraction no longer exhibits an increase with energy.

Conformationally constrained analogues of diacylglycerol. 18. The incorporation of a hydroxamate moiety into diacylglycerol-lactones reduces lipophilicity and helps discriminate between sn-1 and sn-2 binding modes to protein kinase C (PK-C). Implications for isozyme specificity

An approach to reduce the log P in a series of diacylglycerol (DAG)-lactones known for their high binding affinity for protein kinase C (PK-C) is presented. Branched alkyl groups with reduced lipophilicity were selected and combined with the replacement of the ester or lactone oxygens by NH or NOH groups. Compound 6a with an isosteric N-hydroxyl amide arm represents the most potent and least lipophilic DAG analogue known to date.

Molecular characterization and gene expression of lhcb5 gene encoding CP26 in the light-harvesting complex II of Chlamydomonas reinhardtii

We isolated and sequenced a cDNA clone encoding a minor chlorophyll a/b-binding protein, CP26, which is associated with the light-harvesting complex II of Chlamydomonas reinhardtii. Protein sequences of internal peptide fragments from purified CP26 were determined and used to identify a cDNA clone. The 1.1 kb lhcb5 gene codes for a polypeptide of 289 amino acids with a predicted molecular weight of 30,713. The lhcb5 gene product could reconstitute with chlorophylls and xanthophylls to form a green band on a gel. Although the expression of many lhcb genes are strictly regulated by light, the lhcb5 gene was only loosely regulated. We propose that a plant acclimatizes itself to the light environment by quantitatively and qualitatively modulating the light-harvesting complex. Characterization of the primary structure and the implications of its unique expression are discussed.

A textural approach based on Gabor functions for texture edge detection in ultrasound images

Edge detection is an important, but difficult, step in quantitative ultrasound (US) image analysis. In this paper, we present a new textural approach for detecting a class of edges in US images; namely, the texture edges with a weak regional mean gray-level difference (RMGD) between adjacent regions. The proposed approach comprises a vision model-based texture edge detector using Gabor functions and a new texture-enhancement scheme. The experimental results on the synthetic edge images have shown that the performances of the four tested textural and nontextural edge detectors are about 20%-95% worse than that of the proposed approach. Moreover, the texture enhancement may improve the performance of the proposed texture edge detector by as much as 40%. The experiments on 20 clinical US images have shown that the proposed approach can find reasonable edges for real objects of interest with the performance of 0.4 +/- 0.08 in terms of the Pratt's figure.

5-acyloxy-5-hydroxymethyltetrahydro-2-furancarboxylate as a novel template for protein kinase C (PKC) binding

A series of alkyl tetrahydrofuran-2-carboxylates (1-4) bearing a new set of three pharmacophoric groups were tested as protein kinase C (PKC) ligands. The compounds were synthesized from commercially available glycidyl 4-methoxyphenyl ether. The correlation between their binding affinities for PKC-alpha and a conformational fit to phorbol ester indicates they mimic a pharmacophore model comprising the C20-OH, C3-C=O and C9-OH rather than that including the C13-C=O moiety.

Conformationally constrained analogues of diacylglycerol (DAG). 16. How much structural complexity is necessary for recognition and high binding affinity to protein kinase C?

The design of potent protein kinase C (PK-C) ligands with low nanomolar binding affinities was accomplished by the combined use of pharmacophore- and receptor-guided approaches based on the structure of the physiological enzyme activator, diacylglycerol (DAG). Earlier use of the former approach, which was based on the structural equivalence of DAG and phorbol ester pharmacophores, identified a fixed template for the construction of a semirigid "recognition domain" that contained the three principal pharmacophores of DAG constrained into a lactone ring (DAG-lactones). In the present work, the pharmacophore-guided approach was refined to a higher level based on the X-ray structure of the C1b domain of PK-Cdelta complexed with phorbol-13-O-acetate. A systematic search that involved modifying the DAG-lactone template with a combination of linear or branched acyl and alpha-alkylidene chains, which functioned as variable hydrophobic "affinity domains", helped identify compounds that optimized hydrophobic contacts with a group of conserved hydrophobic amino acids located on the top half of the C1 domain where the phorbol binds. The hydrophilic/hydrophobic balance of the molecules was estimated by the octanol/water partition coefficients (log P) calculated according to a fragment-based approach. The presence of branched alpha-alkylidene or acyl chains was of critical importance to reach low nanomolar binding affinities for PK-C. These branched chains appear to facilitate important van der Waals contacts with hydrophobic segments of the protein and help promote the activation of PK-C through critical membrane interactions. Molecular modeling of these DAG-lactones into an empty C1b domain using the program AutoDock 2.4 suggests the existence of competing binding modes (sn-1 and sn-2) depending on which carbonyl is directly involved in binding to the protein. Inhibition of epidermal growth factor (EGF) binding, an indirect PK-C mediated response, was realized with some DAG-lactones at a dose 10-fold higher than with the standard phorbol-12, 13-dibutyrate (PDBU). Through the National Cancer Institute (NCI) 60-cell line in vitro screen, DAG-lactone 31 was identified as a very selective and potent antitumor agent. The NCI's computerized, pattern-recognition program COMPARE, which analyzes the degree of similarity of mean-graph profiles produced by the screen, corroborated our principles of drug design by matching the profile of compound 31 with that of the non-tumor-promoting antitumor phorbol ester, prostratin. The structural simplicity and the degree of potency achieved with some of the DAG-lactones described here should dispel the myth that chemical complexity and pharmacological activity go hand in hand. Even as a racemate, DAG-lactone 31 showed low namomolar binding affinity for PK-C and displayed selective antitumor activity at equivalent nanomolar levels. Our present approach should facilitate the generation of multiple libraries of structurally similar DAG-lactones to help exploit molecular diversity for PK-C and other high-affinity receptors for DAG and the phorbol esters. The success of this work suggests that substantially simpler, high-affinity structures could be identified to function as surrogates of other complex natural products.

Protein kinase C ligands based on tetrahydrofuran templates containing a new set of phorbol ester pharmacophores

A series of substituted tetrahydrofurans with an embedded glycerol backbone carrying additional tetrahydrofuranylideneacetate or tetrahydrofuranylacetate motifs were grouped into four distinct templates (I-IV) according to stereochemistry. The compounds were designed to mimic three essential pharmacophores (C(3)-C=O, C(20)-OH and C(13)-C=O) of the phorbol esters according to a new, revised model. The tetrahydrofuran ring was constructed from glycidyl 4-methoxyphenyl ether, and the structures of the isomeric templates were assigned by NMR spectroscopy, including NOE. The binding affinity for protein kinase C (PKC) was assessed in terms of the ability of the ligands to displace bound [(3)H-20]phorbol 12, 13-dibutyrate (PDBU) from a recombinant alpha isozyme of PKC. Geometric Z- and E-isomers (1 and 3, respectively) containing a tetrahydrofuranylideneacetate motif were the most potent ligands with identical K(i) values of 0.35 microM. Molecular modeling studies of the four templates showed that the rms values when fitted to a prototypical phorbol 12,13-diacetate ester correlated inversely with affinities in the following order: I approximately II > III > IV. These compounds represent the first generation of rigid glycerol templates seeking to mimic the binding of the C(13)-C=O of the phorbol esters. The binding affinities of the most potent compounds are in the same range of the diacylglycerols (DAGs) despite the lack of a phorbol ester C(9)-OH pharmacophore surrogate. This finding confirms that mimicking the binding of the C(13)-C=O pharmacophore of phorbol is a useful strategy. However, since the C(9)-OH and C(13)-C=O in the phorbol esters appear to form an intramolecular hydrogen bond that functions as a combined pharmacophore, it is possible the lack of this combined motif in the target templates restricts the compounds from reaching higher binding affinities.

A comparison of three methods for estimating the requirements for medical specialists: the case of otolaryngologists

OBJECTIVE

To compare three methods of computing the national requirements for otolaryngologists in 1994 and 2010.

DATA SOURCES

Three large HMOs, a Delphi panel, the Bureau of Health Professions (BHPr), and published sources.

STUDY DESIGN

Three established methods of computing requirements for otolaryngologists were compared: managed care, demand-utilization, and adjusted needs assessment. Under the managed care model, a published method based on reviewing staffing patterns in HMOs was modified to estimate the number of otolaryngologists. We obtained from BHPr estimates of work force projections from their demand model. To estimate the adjusted needs model, we convened a Delphi panel of otolaryngologists using the methodology developed by the Graduate Medical Education National Advisory Committee (GMENAC).

DATA COLLECTION/EXTRACTION METHODS

Not applicable.

PRINCIPAL FINDINGS

Wide variation in the estimated number of otolaryngologists required occurred across the three methods. Within each model it was possible to alter the requirements for otolaryngologists significantly by changing one or more of the key assumptions. The managed care model has a potential to obtain the most reliable estimates because it reflects actual staffing patterns in institutions that are attempting to use physicians efficiently.

CONCLUSIONS

Estimates of work force requirements can vary considerably if one or more assumptions are changed. In order for the managed care approach to be useful for actual decision making concerning the appropriate number of otolaryngologists required, additional research on the methodology used to extrapolate the results to the general population is necessary.

An outbreak of tetrodotoxin poisoning following gastropod mollusc consumption

Tetrodotoxin, a violent neurotoxin, is present in puffer fish and may occur in a variety of marine animals. Outbreaks of human tetrodotoxin poisoning, following consumption of marine organisms other than puffer fish, has been rare. We here report an outbreak of tetrodotoxin poisoning following ingestion of gastropod molluscs and its clinical features are discussed. A 71-year-old woman was admitted with hypertension and other neurological symptoms developing after ingestion of some molluscs. A further 16 cases were also found to have typical symptoms of tetrodotoxication after mollusc consumption. Clinical features in these 17 cases were similar to those conventionally found in tetrodotoxin poisoning, except that there was hypertension in eight cases (47%). All except one case had mild poisoning and recovered well. The molluscs consumed comprised two different species: Nassarius castus and Nassarius conoidalis, both of which were shown to contain various amounts of tetrodotoxin. It is concluded that tetrodotoxin poisoning following mollusc consumption is a possibility. Hypertension, as an unusual feature in tetrodotoxication, is frequent in this outbreak, and should be looked for in future cases. The explanation of hypertension in tetrodotoxication may come either from an exaggerated response to sympathetic stimuli, or due to various responses of the vasomotor centre to a small dose of tetrodotoxin. Further studies are required to answer this question.

Chemical crosslinking studies of extrinsic proteins in cyanobacterial photosystem II

Chemical crosslinking with a zero-length crosslinker, 1-ethyl-3-(3-dimethylaminopropyl) carbodimide hydrochloride, was applied to a cyanobacterial photosystem II complex retaining three extrinsic proteins, the 33 kDa manganese-stabilizing protein, cytochrome (cyt) c-550 and the 12 kDa protein. Three major crosslinked products were obtained in addition to the crosslinked product between the extrinsic 33 kDa and the intrinsic CP47 proteins. They were identified to be: cyt c-550-12 kDa; cyt c-550-12 kDa-33 kDa; D2-cyt c-550-12 kDa. These results indicate that the three extrinsic proteins are closely located with each other in cyanobacterial PSII, supporting the previous proposal that, like the 33 kDa protein; cyt c-550 and the 12 kDa protein are associated with PSII at the lumenal side of thylakoids. The results also suggested that the D2 reaction center protein provides a direct binding site for the extrinsic cyt c-550.

A primary mucinous cystoadenocarcinoma of the retroperitoneum

A case of primary retroperitoneal mucinous cystoadenocarcinoma of the ovarian type in the presence of normal ovaries is reported. The histogenesis of this rare tumor has been uncertain. Special immunohistochemical stains done on our specimen show that the histogenesis of this tumor is most likely from mucinous metaplasia of coelomic mesothelium. Three cases of primary retroperitoneal mucinous cystoadenocarcinoma of the ovarian type have previously been reported in the English literature and are reviewed.