Publ.Astron.Soc.Pac.114:721-747,2002 We report the results of a worldwide campaign to observe WZ Sagittae during
its 2001 superoutburst. After a 23-year slumber at V=15.5, the star rose within
2 days ...to a peak brightness of 8.2, and showed a main eruption lasting 25 days.
The return to quiescence was punctuated by 12 small eruptions, of ~1 mag
amplitude and 2 day recurrence time; these "echo outbursts" are of uncertain
origin, but somewhat resemble the normal outbursts of dwarf novae. After 52
days, the star began a slow decline to quiescence.
Periodic waves in the light curve closely followed the pattern seen in the
1978 superoutburst: a strong orbital signal dominated the first 12 days,
followed by a powerful /common superhump/ at 0.05721(5) d, 0.92(8)% longer than
P_orb. The latter endured for at least 90 days, although probably mutating into
a "late" superhump with a slightly longer mean period 0.05736(5) d. The
superhump appeared to follow familiar rules for such phenomena in dwarf novae,
with components given by linear combinations of two basic frequencies: the
orbital frequency omega_o and an unseen low frequency Omega, believed to
represent the accretion disk's apsidal precession. Long time series reveal an
intricate fine structure, with ~20 incommensurate frequencies. Essentially all
components occurred at a frequency n(omega_o)-m(Omega), with m=1, ..., n. But
during its first week, the common superhump showed primary components at n
(omega_o)-Omega, for n=1, 2, 3, 4, 5, 6, 7, 8, 9 (i.e., m=1 consistently); a
month later, the dominant power shifted to components with m=n-1. This may
arise from a shift in the disk's spiral-arm pattern, likely to be the
underlying cause of superhumps.
The great majority of frequency components ... . (etc., abstract continues)
After 10 years of quiescence, HV Vir underwent a superoutburst in January 2002. We report time-series observations clearly revealing the period change of ordinary superhumps during the superoutburst. ...We derived a mean superhump period of 0.058260 d and a positive period derivative of \(7 \times 10^{-5}\). These results are in good agreement with the value obtained from the 1992 superoutburst. We also detected early superhumps, which were not clearly recognized in the past outburst, and a possible rebrightening. Both of them are the common characteristics of WZ Sge-type stars.
We report precise measures of the orbital and superhump period in twenty more dwarf novae. For ten stars, we report new and confirmed spectroscopic periods - signifying the orbital period P_o - as ...well as the superhump period P_sh. These are GX Cas, HO Del, HS Vir, BC UMa, RZ Leo, KV Dra, KS UMa, TU Crt, QW Ser, and RZ Sge. For the remaining ten, we report a medley of P_o and P_sh measurements from photometry; most are new, with some confirmations of previous values. These are KV And, LL And, WX Cet, MM Hya, AO Oct, V2051 Oph, NY Ser, KK Tel, HV Vir, and RX J1155.4-5641. Periods, as usual, can be measured to high accuracy, and these are of special interest since they carry dynamical information about the binary. We still have not quite learned how to read the music, but a few things are clear. The fractional superhump excess epsilon =(P_sh-P_o)/P_o varies smoothly with P_o. The scatter of the points about that smooth curve is quite low, and can be used to limit the intrinsic scatter in M_1, the white dwarf mass, and the mass-radius relation of the secondary. The dispersion in M_1 does not exceed 24%, and the secondary-star radii scatter by no more than 11% from a fixed mass-radius relation. For the well-behaved part of epsilon(P_o) space, we estimate from superhump theory that the secondaries are 18+-6% larger than theoretical ZAMS stars. This affects some other testable predictions about the secondaries: at a fixed P_o, it suggests that the secondaries are (compared with ZAMS predictions) 40+-14% less massive, 12+-4% smaller, 19+-6% cooler, and less luminous by a factor 2.5(7). The presence of a well-defined mass-radius relation, reflected in a well-defined epsilon(P_o) relation, strongly limits effects of nuclear evolution in the secondaries.
We report the results of a worldwide campaign to observe WZ Sagittae during its 2001 superoutburst. After a 23-year slumber at V=15.5, the star rose within 2 days to a peak brightness of 8.2, and ...showed a main eruption lasting 25 days. The return to quiescence was punctuated by 12 small eruptions, of ~1 mag amplitude and 2 day recurrence time; these "echo outbursts" are of uncertain origin, but somewhat resemble the normal outbursts of dwarf novae. After 52 days, the star began a slow decline to quiescence. Periodic waves in the light curve closely followed the pattern seen in the 1978 superoutburst: a strong orbital signal dominated the first 12 days, followed by a powerful /common superhump/ at 0.05721(5) d, 0.92(8)% longer than P_orb. The latter endured for at least 90 days, although probably mutating into a "late" superhump with a slightly longer mean period 0.05736(5) d. The superhump appeared to follow familiar rules for such phenomena in dwarf novae, with components given by linear combinations of two basic frequencies: the orbital frequency omega_o and an unseen low frequency Omega, believed to represent the accretion disk's apsidal precession. Long time series reveal an intricate fine structure, with ~20 incommensurate frequencies. Essentially all components occurred at a frequency n(omega_o)-m(Omega), with m=1, ..., n. But during its first week, the common superhump showed primary components at n (omega_o)-Omega, for n=1, 2, 3, 4, 5, 6, 7, 8, 9 (i.e., m=1 consistently); a month later, the dominant power shifted to components with m=n-1. This may arise from a shift in the disk's spiral-arm pattern, likely to be the underlying cause of superhumps. The great majority of frequency components ... . (etc., abstract continues)
Atomistic scenario of hydrogenation of acetylene to ethylene on the (210)-surface of GaPd. The reaction center is a triangular configuration of two Ga and one neighboring Pd atom. Display omitted
► ...Hydrogenation of acetylene selectively catalyzed by the B20-type GaPd compound is investigated. ► The (210)-surface is the catalytically active surface termination. ► An atomistic scenario for the multi-step hydrogenation process is constructed. ► Reaction centers are triangular configurations of two Ga and one Pd atom. ► Decisive factors for activity and selectivity of the catalyst are discussed.
Recently, it has been demonstrated that intermetallic compounds composed of transition (Pd and Co) and simple (Ga and Al) metals used as catalysts provide excellent efficiency and selectivity for the hydrogenation of acetylene to ethylene. Motivated by experimental work on GaPd catalysts, we have performed a detailed density-functional study of the hydrogenation of acetylene catalyzed by the B20-type GaPd compound. We have identified the pseudo-fivefold (210) surface of the B20 structure as a possible catalytically active surface termination. The atomic structure of the (210) surface can be described by a triangle-rectangle tiling. An atomistic scenario has been constructed for the hydrogenation process catalyzed by this surface. We demonstrate that the active sites for the hydrogenation of acetylene to vinyl and further to ethylene are triangular arrangements of two Ga and one Pd atom atoms. Acetylene is bound to bridge sites formed by two Ga atoms. Vinyl formed in a first hydrogenation step is strongly attached to a Ga atom through its CH group, while the CH2 group shifts toward a neighboring Pd atom. In contrast, ethylene is bound only on top of the Pd atom most strongly protruding from the surface. The activation energies for all steps of the reaction (dissociative adsorption and diffusion of hydrogen, adsorption of all hydrocarbon species, hydrogenation of acetylene to vinyl, of vinyl to ethylene, and of ethylene to ethyl, desorption of ethylene) have been calculated. The activation energies for the rate-controlling steps of 60–70kJ/mol are comparable to those on other catalytically active compounds AlPd and Al13Co4 investigated in previous studies and also comparable or even lower than for a pure Pd catalyst. The desorption energy for ethylene of 45kJ/mol is at least by 14kJ/mol lower than the activation energy of ethylene to ethyl and provides thus excellent selectivity of GaPd. We show that the decisive factors for the activity and selectivity of the catalyst (corrugated surface with slightly protruding transition-metal atoms forming together with two neighboring Al/Ga atoms a triangular arrangement) are essentially the same on all investigated intermetallic compounds GaPd, AlPd, and Al13Co4.
Display omitted
•Semi-hydrogenation of acetylene catalyzed by 3-fold surfaces of GaPd is investigated.•Atomistic scenarios for multi-step hydrogenation processes are constructed.•Decisive factors for ...activity and selectivity of the catalyst are identified.•One of possible 3-fold surfaces exhibits superior catalytic activity and selectivity.•Catalytic properties originate from contributions from surfaces differing in activity and selectivity.
The activity and selectivity of the polar threefold surfaces of the B20-type intermetallic compound GaPd for the semi-hydrogenation of acetylene to ethylene has been investigated using ab initio density functional theory (DFT). Because of the lack of inversion symmetry, the threefold {111} surfaces of the B20 structure have polar character, in both nonequivalent 111 and 1¯1¯1¯ directions several surface terminations differing in structure and chemical composition are possible. The structural and energetic properties and the chemical reactivities of ten conceivable terminations have recently been investigated using DFT (Krajčí and Hafner, 2013) – here detailed atomistic scenarios for the selective semi-hydrogenation of acetylene to ethylene on these surfaces have been developed. Threefold surfaces with only Ga-atoms in the outermost layer are energetically favorable at the Ga-rich end of the interval of the admissible chemical potentials, but they are catalytically inactive because molecular hydrogen cannot be dissociated and hence the hydrogenation of adsorbed hydrocarbon molecules is impossible. Highly corrugated surfaces with Pd atoms in the top atomic plane can hydrogenate adsorbed acetylene molecules easily. But simultaneously their high reactivity with respect to both molecular and atomic hydrogen complicates dissociation and diffusion processes. The selectivity of such surfaces is also insufficient as ethylene molecules adsorbed on-top of highly protruding Pd atoms can be easily attacked by co-adsorbed hydrogen atoms from the bottom. We have found that one of the possible threefold surface terminations with isolated Pd3 triplets and Ga atoms in one-half of the hollows between the Pd3 triplets exhibits both superior catalytic activity and selectivity. However, this surface is energetically competitive only in a very narrow range of chemical potentials. An important factor for achieving a high selectivity is the transition from di-σ bonded adsorption configuration for acetylene to a π-bonded adsorption of ethylene. This transition has also been found in our earlier investigation of the (210) surface of GaPd as a catalyst for semi-hydrogenation (Krajčí and Hafner, 2012). The large distances between the isolated active sites is also important to avoid undesired side-reactions such as oligomerization. Our results are well compatible with the available experimental observations. We have demonstrated that the observed activity and selectivity of GaPd catalyst originate form contributions from different surfaces terminations differing in activity and selectivity. An optimal selectivity of the catalyst can be achieved only if the formation of surfaces with low selectivity is avoided and terminations with enhanced selectivity are formed.
Slovakia conducted multiple rounds of population-wide rapid antigen testing for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in late 2020, combined with a period of additional contact ...restrictions. Observed prevalence decreased by 58% (95% confidence interval: 57 to 58%) within 1 week in the 45 counties that were subject to two rounds of mass testing, an estimate that remained robust when adjusting for multiple potential confounders. Adjusting for epidemic growth of 4.4% (1.1 to 6.9%) per day preceding the mass testing campaign, the estimated decrease in prevalence compared with a scenario of unmitigated growth was 70% (67 to 73%). Modeling indicated that this decrease could not be explained solely by infection control measures but required the addition of the isolation and quarantine of household members of those testing positive.
To date, extended-release naltrexone hydrochloride has not previously been compared directly with opioid medication treatment (OMT), currently the most commonly prescribed treatment for opioid ...dependence.
To determine whether treatment with extended-release naltrexone will be as effective as daily buprenorphine hydrochloride with naloxone hydrochloride in maintaining abstinence from heroin and other illicit substances in newly detoxified individuals.
A 12-week, multicenter, outpatient, open-label randomized clinical trial was conducted at 5 urban addiction clinics in Norway between November 1, 2012, and December 23, 2015; the last follow-up was performed on October 23, 2015. A total of 232 adult opioid-dependent (per DSM-IV criteria) individuals were recruited from outpatient addiction clinics and detoxification units and assessed for eligibility. Intention-to-treat analyses of efficacy end points were performed with all randomized participants.
Randomization to either daily oral flexible dose buprenorphine-naloxone, 4 to 24 mg/d, or extended-release naltrexone hydrochloride, 380 mg, administered intramuscularly every fourth week for 12 weeks.
Primary end points (protocol) were the randomized clinical trial completion rate, the proportion of opioid-negative urine drug tests, and number of days of use of heroin and other illicit opioids. Secondary end points included number of days of use of other illicit substances. Safety was assessed by adverse event reporting.
Of 159 participants, mean (SD) age was 36 (8.6) years and 44 (27.7%) were women. Eighty individuals were randomized to extended-release naltrexone and 79 to buprenorphine-naloxone; 105 (66.0%) completed the trial. Retention in the extended-release naltrexone group was noninferior to the buprenorphine-naloxone group (difference, -0.1; with 95% CI, -0.2 to 0.1; P = .04), with mean (SD) time of 69.3 (25.9) and 63.7 (29.9) days, correspondingly (P = .33, log-rank test). Treatment with extended-release naltrexone showed noninferiority to buprenorphine-naloxone on group proportion of total number of opioid-negative urine drug tests (mean SD, 0.9 0.3 and 0.8 0.4, respectively, difference, 0.1 with 95% CI, -0.04 to 0.2; P < .001) and use of heroin (mean difference, -3.2 with 95% CI, -4.9 to -1.5; P < .001) and other illicit opioids (mean difference, -2.7 with 95% CI, -4.6 to -0.9; P < .001). Superiority analysis showed significantly lower use of heroin and other illicit opioids in the extended-release naltrexone group. No significant differences were found between the treatment groups regarding most other illicit substance use.
Extended-release naltrexone was as effective as buprenorphine-naloxone in maintaining short-term abstinence from heroin and other illicit substances and should be considered as a treatment option for opioid-dependent individuals.
clinicaltrials.gov Identifier: NCT01717963.
We summarize the results of a 20-yr campaign to study the light curves of BK Lyn, a nova-like star strangely located below the 2 to 3 h orbital-period gap in the family of cataclysmic variables ...(CVs). Two apparent superhumps dominate the nightly light curves, with periods 4.6 per cent longer, and 3.0 per cent shorter, than the orbital period. The first appears to be associated with the star's brighter states (V ∼ 14), while the second appears to be present throughout and becomes very dominant in the low state (V ∼ 15.7). It is plausible that these arise, respectively, from a prograde apsidal precession and a retrograde nodal precession of the star's accretion disc. Starting in the year 2005, the star's light curve became indistinguishable from that of a dwarf nova - in particular, that of the ER UMa subclass. No such clear transition has ever been observed in a CV before. Reviewing all the star's oddities, we speculate: (a) BK Lyn is the remnant of the probable nova on 101 December 30, and (b) it has been fading ever since, but it has taken ∼2000 yr for the accretion rate to drop sufficiently to permit dwarf-nova eruptions. If such behaviour is common, it can explain other puzzles of CV evolution. One: why the ER UMa class even exists (because all members can be remnants of recent novae). Two: why ER UMa stars and short-period nova-likes are rare (because their lifetimes, which are essentially cooling times, are short). Three: why short-period novae all decline to luminosity states far above their true quiescence (because they are just getting started in their post-nova cooling). Four: why the orbital periods, accretion rates and white dwarf temperatures of short-period CVs are somewhat too large to arise purely from the effects of gravitational radiation (because the unexpectedly long interval of enhanced post-nova brightness boosts the mean mass-transfer rate). And maybe even five: why very old, post-period-bounce CVs are hard to find (because the higher mass-loss rates have 'burned them out'). These are substantial rewards in return for one investment of hypothesis: that the second parameter in CV evolution, besides orbital period, is time since the last classical-nova eruption.
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