Coherent optical clock down-conversion for microwave frequencies with 10-18 instability

Optical atomic clocks are poised to redefine the Système International (SI) second, thanks to stability and accuracy more than 100 times better than the current microwave atomic clock standard. However, the best optical clocks have not seen their performance transferred to the electronic domain, where radar, navigation, communications, and fundamental research rely on less stable microwave sources. By comparing two independent optical-to-electronic signal generators, we demonstrate a 10-gigahertz microwave signal with phase that exactly tracks that of the optical clock phase from which it is derived, yielding an absolute fractional frequency instability of 1 × 10^-18 in the electronic domain. Such faithful reproduction of the optical clock phase expands the opportunities for optical clocks both technologically and scientifically for time dissemination, navigation, and long-baseline interferometric imaging.

Optical-Clock-Based Time Scale

A time scale is a procedure for accurately and continuously marking the passage of time. It is exemplified by Coordinated Universal Time (UTC) and provides the backbone for critical navigation tools such as the Global Positioning System. Present time scales employ microwave atomic clocks, whose attributes can be combined and averaged in a manner such that the composite is more stable, accurate, and reliable than the output of any individual clock. Over the past decade, clocks operating at optical frequencies have been introduced that are orders of magnitude more stable than any microwave clock. However, in spite of their great potential, these optical clocks cannot be operated continuously, which makes their use in a time scale problematic. We report the development of a hybrid microwave-optical time scale, which only requires the optical clock to run intermittently while relying upon the ensemble of microwave clocks to serve as the flywheel oscillator. The benefit of using a clock ensemble as the flywheel oscillator instead of a single clock can be understood by the Dick-effect limit. This time scale demonstrates for the first time subnanosecond accuracy over a few months, attaining a fractional frequency stability of 1.45 × 10-16 at 30 days and reaching the 10-17 decade at 50 days, with respect to UTC. This time scale significantly improves the accuracy in timekeeping and could change the existing time-scale architectures.

Oscillator metrology with software defined radio

Analog electrical elements such as mixers, filters, transfer oscillators, isolating buffers, dividers, and even transmission lines contribute technical noise and unwanted environmental coupling in time and frequency measurements. Software defined radio (SDR) techniques replace many of these analog components with digital signal processing (DSP) on rapidly sampled signals. We demonstrate that, generically, commercially available multi-channel SDRs are capable of time and frequency metrology, outperforming purpose-built devices by as much as an order-of-magnitude. For example, for signals at 10 MHz and 6 GHz, we observe SDR time deviation noise floors of about 20 fs and 1 fs, respectively, in under 10 ms of averaging. Examining the other complex signal component, we find a relative amplitude measurement instability of 3 × 10(-7) at 5 MHz. We discuss the scalability of a SDR-based system for simultaneous measurement of many clocks. SDR's frequency agility allows for comparison of oscillators at widely different frequencies. We demonstrate a novel and extreme example with optical clock frequencies differing by many terahertz: using a femtosecond-laser frequency comb and SDR, we show femtosecond-level time comparisons of ultra-stable lasers with zero measurement dead-time.

Usage Analysis of the NIST Internet Time Service

The Internet Time Service (ITS) at the National Institute of Standards and Technology (NIST) currently receives over 16 billion time requests per day. ITS servers derive their system time from the NIST atomic-referenced time scale and distribute it freely to the public. Here we explore ITS usage patterns discovered by analysis of inbound network traffic. For example, over a period of four weeks, just two of the ≈ 20 ITS servers received requests from 316 million unique Internet Protocol (IPv4) addresses, which is at least 8.5 % of the entire Internet. We offer recommendations for networked device/software manufacturers, and providers and consumers of network time services.

Atomic clock with 1×10(-18) room-temperature blackbody Stark uncertainty

The Stark shift due to blackbody radiation (BBR) is the key factor limiting the performance of many atomic frequency standards, with the BBR environment inside the clock apparatus being difficult to characterize at a high level of precision. Here we demonstrate an in-vacuum radiation shield that furnishes a uniform, well-characterized BBR environment for the atoms in an ytterbium optical lattice clock. Operated at room temperature, this shield enables specification of the BBR environment to a corresponding fractional clock uncertainty contribution of 5.5×10(-19). Combined with uncertainty in the atomic response, the total uncertainty of the BBR Stark shift is now 1×10(-18). Further operation of the shield at elevated temperatures enables a direct measure of the BBR shift temperature dependence and demonstrates consistency between our evaluated BBR environment and the expected atomic response.

Experimental recovery of a qubit from partial collapse

We describe and implement a method to restore the state of a single qubit, in principle perfectly, after it has partially collapsed. The method resembles the classical Hahn spin echo but works on a wider class of relaxation processes, in which the quantum state partially leaves the computational Hilbert space. It is not guaranteed to work every time, but successful outcomes are heralded. We demonstrate, using a single trapped ion, a better performance from this recovery method than can be obtained employing projection and postselection alone. The demonstration features a novel qubit implementation that permits both partial collapse and coherent manipulations with high fidelity.

High-accuracy measurement of atomic polarizability in an optical lattice clock

Presently, the Stark effect contributes the largest source of uncertainty in a ytterbium optical atomic clock through blackbody radiation. By employing an ultracold, trapped atomic ensemble and high stability optical clock, we characterize the quadratic Stark effect with unprecedented precision. We report the ytterbium optical clock's sensitivity to electric fields (such as blackbody radiation) as the differential static polarizability of the ground and excited clock levels α(clock) = 36.2612(7)  kHz (kV/cm)(-2). The clock's uncertainty due to room temperature blackbody radiation is reduced by an order of magnitude to 3×10(-17).

p-Wave cold collisions in an optical lattice clock

We study ultracold collisions in fermionic ytterbium by precisely measuring the energy shifts they impart on the atoms' internal clock states. Exploiting Fermi statistics, we uncover p-wave collisions, in both weakly and strongly interacting regimes. With the higher density afforded by two-dimensional lattice confinement, we demonstrate that strong interactions can lead to a novel suppression of this collision shift. In addition to reducing the systematic errors of lattice clocks, this work has application to quantum information and quantum simulation with alkaline-earth atoms.

Homework assignments, consequences, and classroom performance in social studies and mathematics

Elementary school students who frequently answered questions incorrectly in class were given daily homework assignments in social studies and math, but they rarely completed the assignments accurately and their classroom performance in social studies and math was only slightly better than when they did not have homework assignments. However, consequences provided for accurate completion of homework assignments increased the number of students completing homework and the accuracy with which homework assignments were completed. Further, assignments of homework with consequences for accuracy were associated with more accurate classroom performance.

Effects of peer tutoring and consequences on the math performance of elementary classroom students

The effects of unstructured peer-tutoring procedures on the math performance of fourth- and fifth-grade students were investigated. Students' performances in two daily math sessions, during which they worked problems of the same type and difficulty, were compared. When students tutored each other over the same math problems as they subsequently worked, higher accuracies and rates of performance were associated with the tutored math sessions. The use of consequences for accurate performance seemed to enhance the effects of tutoring on accuracy. The results from an independent-study control condition, which was the same peer-tutoring except that students did not interact with each other, suggested that interactions between students during the tutoring procedure were, in part, responsible for improved accuracy and rate of performance. When students tutored each other over different but related problems to those that they were subsequently asked to solve, accuracies and rates during tutored math sessions were also higher, suggesting the development of generalized skills in solving particular types of math problems.

Effects of choice and immediacy of reinforcement on single response and switching behavior of children

Children responded on a single operandum to produce marbles or candy within a two-component multiple schedule and then were allowed to choose which component was in effect. Experiment I examined the effects of exchanging marbles after sessions for subject-selected or experimenter-selected candy. Rate of response to the single operandum was not affected. However, when the subjects could switch components, they spent the majority of time and responded at somewhat higher rates in a component where marbles were exchangable for subject-selected candy. Experiment II examined the effects of eliminating the immediate marble consequence for responses. Rate of response to the single operandum was not affected. However, when subjects could switch components they spent more time in a component where immediate marble consequences were available for responses, than where no immediate marble consequences were available.

An experimental analysis of verbal imitation in preschool children

A model presented English words to three preschool children and reinforced accurate imitation of these words. The model also presented novel Russian words but the subjects' imitation of these words was never reinforced. As long as the subjects' imitation of English words was reinforced, their accuracy of imitating non-reinforced Russian words increased. When reinforcement was not contingent upon imitation of English words, accuracy of imitating both the English and the Russian words decreased. These results support and extend previous work on imitation.

Training generative verb usage by imitation and reinforcement procedures

Three retarded children were trained, using imitation and reinforcement procedures, to produce past and present tense forms of verbs in response to verbal requests. Two types of experimental sessions were arranged: training sessions and probe sessions. During training sessions, a child was trained to produce one verb in both the past and the present tense. Then, in a probe session, the generalization of this training was tested by presenting to the child a series of untrained verbs interspersed with previously trained verbs. Responses to untrained verbs were never reinforced. Training sessions alternated with probe sessions throughout a multiple baseline design involving four classes of verb inflections as the baselines. The results showed that, as past and present tense forms of verbs within an inflectional class were trained, the children correctly produced past and present tense forms of untrained verbs within this class. When verbs from two or more classes were trained, the children correctly produced the verb tenses from each of these classes. Thus, the imitation and reinforcement procedures were effective in teaching generative use of verb inflections.

Some factors controlling preference between fixed-ratio and variable-ratio schedules of reinforcement

A multiple schedule of food reinforcement for key-pecking was arranged which consisted of nine fixed-ratios, each of which operated in the presence of a different stimulus. Pigeons could complete a given fixed-ratio within the multiple schedule or, by pecking a second key, could switch from the fixed-ratio schedule to a variable-ratio schedule consisting of the same nine ratios. Stable switching behavior was established which did not maximize simple probability or rate of reinforcement. Instead, the subjects showed a stable preference for the variable-ratio schedule of food reinforcement. Increasing the number of responses required to switch, and removing the occasions on which reinforcement was delivered after a single response in the variable schedule, decreased the number of switches to the variable schedule. Periods of delay interposed between a completed switch and the availability of reinforcement after one response in the variable schedule also decreased switching to the variable schedule, particularly at long delay intervals.

Use and analysis of the "Good Behavior Game" to reduce disruptive classroom behavior

A recent study reported procedures (the "good behavior game") for reducing disruptive classroom behavior. Replication of the procedures of the "good behavior game" in two classrooms showed it to be an effective technique for reducing disruptive talking and out-of-seat behavior. Further experimental analysis indicated that the effective components of the game were division of the class into teams, consequences for a team winning the game, and criteria set for winning the game. Although disruptive behavior was markedly reduced by the game, the reductions were correlated with only slightly improved accuracy of academic performance in the one classroom where academic performance was measured.

An analysis of daily report cards and parent-managed privileges in the improvement of adolescents' classroom performance

A daily report-card system, involving home privileges administered by parents, was developed for use with "problem" junior-high students. In Experiment I, when home privileges and parent praise were contingent on improved school conduct, classwork, daily grades, and teacher satisfaction, the school performance of three students improved considerably. In Experiment II, a similar report-card system was employed with two additional students, except only parent praise was contingent on improved school performance. Under these conditions, one of the students did not bring the report card home, and class performance did not improve until contingent home privileges were added. The school performance of the second student improved with the card and praise alone. However, there appeared to be a slow decline of classwork performance over time. For Experiment III, an instructional manual, describing the report-card program, was written for school guidance counsellors. Two guidance counsellors read the program, used it with one student each, and found that the school performance of both students improved. These results suggest that the daily report-card program with home consequences administered by parents can improve the school performance of, and teacher satisfaction about, students having considerable difficulty in school.

Effects of a conditioned reinforcer upon accuracy of match-to-sample behavior in pigeons

Three pigeons were trained to perform a two-key sequential match-to-sample task. During baseline conditions, food reinforcement was contingent upon the first match response to occur following 8-min periods, and orange illumination of both keys preceded the delivery of food by 0.5 sec. The baseline schedule of food reinforcement was in effect throughout the study. In some conditions, a 0.5-sec flash of orange keylight alone was presented contingent upon mismatch responses that followed variable time periods averaging 1 min. Rate of mismatch responses increased and accuracy of matching performances decreased as compared with baseline conditions. The ability of the 0.5-sec orange flash to reinforce mismatch responses was markedly reduced when it no longer immediately preceded the delivery of food.

High-fidelity readout of trapped-ion qubits

We demonstrate single-shot qubit readout with a fidelity sufficient for fault-tolerant quantum computation. For an optical qubit stored in 40Ca+ we achieve 99.991(1)% average readout fidelity in 10(6) trials, using time-resolved photon counting. An adaptive measurement technique allows 99.99% fidelity to be reached in 145 micros average detection time. For 43Ca+, we propose and implement an optical pumping scheme to transfer a long-lived hyperfine qubit to the optical qubit, capable of a theoretical fidelity of 99.95% in 10 micros. We achieve 99.87(4)% transfer fidelity and 99.77(3)% net readout fidelity.

Plasminogen and plasmin activity in patients with coronary artery disease

OBJECTIVE

While coronary artery disease (CAD) is associated with disturbances of the plasma fibrinolytic system, the nature of these disturbances is not fully defined. Fibrinolysis is regulated by plasmin, whose production is mediated by plasminogen activator conversion of plasminogen (Plg) to plasmin. The cascade is modulated by feedback loops that include Plg activator inhibitor 1 (PAI-1). Molecular interactions with Plg kringle domains play an important role in regulating plasmin production and its modulation of fibrinolysis. We hypothesized that interactions of tissue plasminogen activator (tPA) with Plg kringle domains regulates plasmin levels in patients with stable CAD.

METHODS

Plasma was collected from patients (n = 33) with an angiographically significant CAD and controls (n = 18) with angiographically established normal or minimally diseased arteries. Plasmin activity, tPA activity, and plasma levels of Plg, PAI-1, uPA, and tPA were determined.

RESULTS

CAD patients had 1.7-fold greater plasmin activity (P = 0.02) that correlated with 1.5-fold higher tPA activity when compared to controls. Epitope mapping of Plg domains showed Plg differences in epitope exposure between the two groups. Plasma from CAD patients had 50% less (P < 0.001) detectable kringle 4 and 48% less (P = 0.007) detectable kringles 1-3.

CONCLUSIONS

Based on detectable differences in Plg, we conclude that in patients with stable CAD, Plg complexed with tPA exists in a conformation that enables increased tPA activity and Plg conversion to plasmin.

FDG-PET. A possible prognostic factor in head and neck cancer

Previous studies have shown that high uptake of (18)F-fluoro-2-deoxy-glucose in head and neck cancer, as determined by the standardized uptake value on positron emission tomography scan, was associated with poor survival. The aim of this study was to confirm the association and to establish whether a high standardized uptake value had prognostic significance. Seventy-three consecutive patients with newly diagnosed squamous cell carcinoma of the head and neck underwent a positron emission tomography study before treatment. Age, gender, performance status tumour grade, stage, maximal tumour diameter and standardized uptake value were analyzed for their possible association with survival. The median standardized uptake value for all primary tumours was 7.16 (90% range 2.30 to 18.60). In univariate survival analysis the cumulative survival was decreased as the stage, tumour diameter and standardized uptake value increased. An standardized uptake value of 10 was taken as a cut-off for high and low uptake tumours. When these two groups were compared, an standardized uptake value >10 predicted for significantly worse outcome (P=0.003). Multivariate analysis demonstrated that an standardized uptake value >10 provided prognostic information independent of the tumour stage and diameter (P=0.002). We conclude that high FDG uptake (standardized uptake value>10) on positron emission tomography is an important marker for poor outcome in primary squamous cell carcinoma of the head and neck. Standardized uptake value may be useful in distinguishing those tumours with a more aggressive biological nature and hence identifying patients that require intensive treatment protocols including hyperfractionated radiotherapy and/or chemotherapy.

A rapidly expanding lesion in the neck: unusual presentation of Castleman's disease

We report a painless but rapidly enlarging 9 cm x 4 cm lobulated hard neck mass. CT scanning suggested lymphoid tissue that was not confirmed by cytopathology. Histopathological analysis of the excision specimen detected Castleman's disease, extending to the resection margin. Postoperative radiotherapy was administered. The patient remains disease-free after 44 months.

Ultracision: the harmonic scalpel and its possible uses in maxillofacial surgery

We report on the potential uses and benefits of a new development in incisive technology. The harmonic scalpel uses high-frequency mechanical energy to offer the surgeon controlled and precise incision and haemostasis. Vessels up to 2 mm in diameter may be sealed by coaptation with the blade before division. No special training or precautions are required before using this self-cleaning device. It produces considerably less smoke or smell than either diathermy or laser, which reduces the need for instrument exchanges and smoke evacuation. We think that it will be useful for tongue resections and possibly for neck dissections.

Management of severe postnasal haemorrhage: the Kingsley splint revisited

Postnasal haemorrhage accompanying severe craniofacial trauma may have catastrophic consequences if not arrested promptly. The airway has usually been secured and the cervical spine stabilized, but apart from fluid replacement, other attempts to control haemorrhage in the resuscitation room of the accident and emergency department may be to no avail. We wish to draw attention to a simple device that was introduced over 100 years ago and which may rapidly aid haemostasis and prevent the onset of hypovolaemic shock.

Lack of correlation between water hardness and salivary calculi in England

Our aim was to test the hypothesis that residents of hard water areas are at increased risk of developing salivary calculi. The evidence based on figures from the Hospital Episode Statistics database for the years 1991 to 1994, suggests that there is no such association. For example, in the South West Water area (soft water) the incidence was 28.92/million/year compared with Yorkshire (hard water) 31.64/million/year. The correlation coefficient shows that water hardness is not significantly associated with either the incidence of salivary calculi (r = 0.02, P = 0.9) or that of sialadenitis (n = 2.4, P = 0.4). The lack of association holds for both men and women independently. However, the two conditions have similar patterns of incidence (r = 0.5, P = 0.05), suggesting some common but unknown similarity in aetiology.

Effects of deprivation on engagement in preferred activities by persons with developmental disabilities

This study examined the effects of deprivation on engagement in activities for 3 adult men with developmental disabilities. First, an assessment was conducted to identify a high- and a low-preference activity for each participant. Second, the high-preference activity was made available following three amounts of deprivation of the activity (15 min, 2 hr, and 1 to 4 days); the low-preference activity was made available following the schedule of deprivation that produced the highest level of engagement by each participant in the high-preference activity. The results were that 1 to 4 days of deprivation produced the highest average amounts of engagement in the high-preference activity for each participant; this amount of deprivation did not produce high engagement in the low-preference activities. Third, the deprivation procedures and results were replicated when high-preference activities were presented by teachers during the participants' daily activities when their engagement had been quite low.

Reducing disruptive behavior of a group-home resident with autism and mental retardation

A treatment package consisting of a DRO procedure, token fines, and prompted relaxation was used to reduce the agitated-disruptive behavior of a person with autism and mental retardation living in a community group home. The agitated-disruptive behaviors (cursing, hitting, kicking, throwing objects, and verbal threats) were measured during three different activities in a group home. The baseline rates of the agitated-disruptive behavior during one of these activities was relatively low, during another was moderate, and during the third was high. DRO procedures were partially implemented by a peer with Down syndrome and mental retardation during a portion of the study. Effects of the DRO procedures were as follows: During each activity an initial reduction of agitated-disruptive behavior was dependent on choosing an appropriate DRO interval, with shorter DRO intervals required during activities in which the baseline rates of the agitated-disruptive behavior were higher. Once shorter DRO intervals had been used to reduce agitated-disruptive behavior, longer DRO intervals were effective in maintaining those reductions. Reductions were maintained for up to 6 months.

The radiosurgical approach to biopsy

The use of radiosurgery to remove a lesion for biopsy facilitates the time and effectiveness of the procedure. The hemostatic properties of the radiowave affords the practitioner a better field of visibility, enabling the procedure to be done in a safe, timely fashion.

Expression of retinoic acid receptors in normal, dysplastic and malignant oral epithelia

Chemoprevention with retinoic acid (RA) derivatives may reduce the incidence of transformation of potentially malignant oral lesions, and help prevent development of second primary tumours in the upper aerodigestive tract. At present, little is known about the mechanisms by which RA derivatives modify cell proliferation and differentiation. RA interacts with two classes of nuclear receptors: the retinoic acid receptors (RARs) and retinoid X receptors (RXRs). We have used immunohistology to localise these receptors on normal epidermis and oral mucosa. The distribution of RAR and RXR suggests that RA may exert complex growth regulatory effects on oral mucosa. Increased levels of RAR and RXR, together with alterations in the patterns of expression of these receptors, were seen when dysplastic and malignant epithelia were compared to normal oral mucosa. These findings suggest that expression of RAR and RXR receptors is modulated in epithelia showing altered growth regulation.

Regulation of the mRNA-binding protein AUF1 by activation of the beta-adrenergic receptor signal transduction pathway

In both cell culture based model systems and in the failing human heart, beta-adrenergic receptors ( beta-AR) undergo agonist-mediated down-regulation. This decrease correlates closely with down-regulation of its mRNA, an effect regulated in part by changes in mRNA stability. Regulation of mRNA stability has been associated with mRNA-binding proteins that recognize A + U-rich elements within the 3'-untranslated regions of many mRNAs encoding proto-oncogene and cytokine mRNAs. We demonstrate here that the mRNA-binding protein, AUF1, is present in both human heart and in hamster DDT1-MF2 smooth muscle cells and that its abundance is regulated by beta-AR agonist stimulation. In human heart, AUF1 mRNA and protein was significantly increased in individuals with myocardial failure, a condition associated with increases in the beta-adrenergic receptor agonist norepinephrine. In the same hearts, there was a significant decrease (approximately 50%) in the abundance of beta1-AR mRNA and protein. In DDT1-MF2 cells, where agonist-mediated destabilization of beta2-AR mRNA was first described, exposure to beta-AR agonist resulted in a significant increase in AUF1 mRNA and protein (approximately 100%). Conversely, agonist exposure significantly decreased (approximately 40%) beta2-adrenergic receptor mRNA abundance. Last, we demonstrate that AUF1 can be immunoprecipitated from polysome-derived proteins following UV cross-linking to the 3'-untranslated region of the human beta1-AR mRNA and that purified, recombinant p37AUF1 protein also binds to beta1-AR 3'-untranslated region mRNA.

The traY gene product and integration host factor stimulate Escherichia coli DNA helicase I-catalyzed nicking at the F plasmid oriT

F plasmid conjugative transfer is initiated by the introduction of a site- and strand-specific nick within the plasmid origin of transfer (oriT). Genetic studies have shown nick formation to be dependent on both the traI and traY genes. However, highly purified TraIp, the traI gene product, nicks oriT in a site- and strand-specific manner in the absence of the traY gene product (TraYp) in vitro (Matson, S.W., and Morton, B.S. (1991) J. Biol. Chem. 266, 16232-16237). Analysis of the oriT region has revealed binding sites for TraYp and the host protein integration host factor (IHF). To explore possible interactions occurring at oriT, highly purified TraIp, TraYp, and IHF were incubated with a supercoiled oriT-containing DNA substrate. A marked enhancement of the nicking reaction catalyzed by TraIp was observed in a reaction that required both TraYp and IHF. In addition, TraIp was able to nick a linear oriT-containing double-stranded DNA substrate when IHF and TraYp were present in the reaction; such a substrate is not nicked by TraIp alone. Individual protein concentration requirements for the supercoiled and linear nicking reactions were similar, and the reactions occurred at equal velocity, suggesting that they are biochemically identical. Concentrations of TraYp and IHF that yield half-maximal activity in the nicking assays compare well with the reported KD values for the IHF and TraYp binding sites in oriT. These data, coupled with data presented in the accompanying report, suggest that TraYp and IHF bind independent of one another, forming a nucleo-protein complex with oriT that can be recognized and nicked by TraIp.

Escherichia coli DNA helicase I catalyzes a sequence-specific cleavage/ligation reaction at the F plasmid origin of transfer

Recent studies have shown that the Escherichia coli F plasmid-encoded traI gene product (TraIp), also known as DNA helicase I, catalyzes the formation of the site- and strand-specific nick that initiates F plasmid DNA transfer. Scission of the phosphodiester bond at the nic site within the origin of transfer (oriT) is accompanied by the covalent attachment of TraIp to the 5'-phosphate of the nicked DNA strand. This mechanism suggests that TraIp may also be capable of catalyzing a DNA ligation reaction using the energy stored in the protein-DNA intermediate. To test this possibility, an in vitro assay was designed that utilized short single-stranded DNA oligonucleotides of different lengths derived from the region within oriT that spanned the nic site. Purified TraIp was capable of efficiently cleaving single-stranded DNA that contained a nic site, and upon cleavage, the protein became covalently linked to the 5'-end of the nic site. When TraIp was incubated with two oligonucleotides of different length that contained the nic site, there was formation of novel recombinant products resulting from a TraIp-catalyzed cleavage/ligation reaction. Furthermore, the cleavage and ligation reactions were both sequence-specific. These data suggest that TraIp plays an important role in the initiation and termination of conjugative DNA transfer.

Choice and control. New opportunities for people with developmental disabilities

Over the past few years, people with developmental disabilities have had an increasing number of opportunities to make choices and have control over their lives. There has also been a considerable amount of experimental research conducted on the effects of providing opportunities to make choices or to exercise control. The results of this research strongly suggest that providing opportunities for choice and control over events can affect the degree to which people participate in activities, the types of behaviors displayed during the participation, and people's perceptions about the situation. This article reviews this experimental research, discusses traditional views and current perspectives regarding choice and control for people with developmental disabilities, and presents ways of increasing the amount of choice and control available to people with developmental disabilities.

Ongoing consultation as a method of improving performance of staff members in a group home

A model of ongoing consultation was implemented in a community group home for 8 adults with severe and profound mental retardation. Two consultants, highly experienced in working with people with mental retardation and in the procedures used in group homes, taught staff members to use a token reinforcement system, to engage the adults in a variety of activities, and to improve the content and style of the staff members' interactions with the adults. The consultants taught skills to 9 staff members through brief mini-workshops, direct observation of the staff members' use of the skills during regular activities in the group home, and individual verbal feedback regarding a staff member's performance of the skills. Evaluation of the ongoing consultation process by the 2 consultants showed it to be effective in improving the performance of the staff members and in changing the behaviors of the adults who lived in the home. Continued implementation of the process, however, appeared to be necessary for the behavior changes of staff members to be maintained at high levels.

Social evaluation of behaviors comprising three social skills and a comparison of the performance of people with and without mental retardation

We evaluated whether behaviors commonly taught to persons with mental retardation as part of three important social skills (following instructions, accepting criticism, and negotiating to resolve conflicts) were responded to favorably by other people. People with mental retardation who lived in the community and other people from the community participated in videotaped role plays involving each of the social skills. The performances of participants were scored according to behavioral checklists. Participants with mental retardation scored as well as other participants on following instructions and accepting criticism but lower on negotiating. Community members were asked to evaluate how well the participants did in the videotaped role-play situations. There were high positive correlations between the scores derived from the behavioral checklists and the evaluations of community members for both groups of participants.

Social validation of component behaviors of following instructions, accepting criticism, and negotiating

This study evaluated whether behaviors often taught as part of social skills training are judged favorably by others. Community judges evaluated the performances of people in various situations requiring one of three social skills: following instructions, accepting criticism, and negotiating to resolve conflicts. These skills were displayed in videotaped scenes by actors with and without mental retardation who acted out roles that had different types of authority relationships, and when different components or clusters of behavior (nonverbal, specific verbal, or general verbal behaviors) were performed well or poorly. The highest ratings by judges were of videotaped scenes that depicted correct use of all behaviors, regardless of which skill was being examined, whether or not the actor had mental retardation, or what the relationship was between the two actors. The lowest ratings were of videotaped scenes that depicted poor performance of all behaviors, and intermediate ratings were obtained when only some of the behaviors were performed poorly. These results, as well as the verbal responses of judges to questions, indicated that the different behaviors commonly used in teaching the skills of following instructions, accepting criticism, and negotiating are relevant to judgment of social performance, and are likely to be reinforced and maintained by social contingencies.

In-home generalization of social interactions in families of adolescents with behavior problems

The effects of a three-phase family communication program were evaluated. In the skill-teaching phase, family members were taught reciprocal social communication skills in a clinic setting. During the skill-review phase, each family member practiced the skills in their homes with the teacher. During the home-based family conference phase, each family was taught to use a structured format to resolve current family issues using their newly acquired skills. In-home parent-youth interactions were observed during a series of 1-hr sessions that involved directed and nondirected situations. Evaluation included a multiple baseline design across skills during the skill-teaching phase and a multiple baseline design across families for the family conference phase. Although the procedures of the skill-teaching phase resulted in parent-adolescent dyads learning to use the skills in the teaching setting, competent use of the skills in the home was not observed until the family conference phase was implemented. These results suggest the importance of home-based intervention if changes are to be obtained at home.

Teaching adults with severe and profound retardation to exit their homes upon hearing the fire alarm

Prompting, modeling, and differential reinforcement with client-chosen rewards were used to teach 3 nonverbal people with severe to profound mental retardation to exit their group homes at the sound of the house fire alarm, using a multiple baseline design. All 3 participants learned to exit independently in less than 2 min in all experimenter-initiated surprise fire drills and in the majority of staff-initiated surprise fire drills. Each participant was also able to exit from five areas of the house from which teaching was not done.

Balancing the right to habilitation with the right to personal liberties: the rights of people with developmental disabilities to eat too many doughnuts and take a nap

In the pursuit of efficient habilitation, many service providers exercise a great deal of control over the lives of clients with developmental disabilities. For example, service providers often choose the client's habilitative goals, determine the daily schedule, and regulate access to preferred activities. This paper examines the advantages and disadvantages of allowing clients to exercise personal liberties, such as the right to choose and refuse daily activities. On one hand, poor choices on the part of the client could hinder habilitation. On the other hand, moral and legal issues arise when the client's right to choice is abridged. Recommendations are offered to protect both the right to habilitation and the freedom to choose.