ABSTRACT
Second-order nonlinear optical interactions such as sum- and difference-frequency generation are widely used for bioimaging and as selective probes of interfacial environments. However, inefficient nonlinear optical conversion often leads to poor signal-to-noise ratio and long signal acquisition times. Here, we demonstrate the dramatic enhancement of weak second-order nonlinear optical signals via stimulated sum- and difference-frequency generation. We present a conceptual framework to quantitatively describe the interaction and show that the process is highly sensitive to the relative optical phase of the stimulating field. To emphasize the utility of the technique, we demonstrate stimulated enhancement of second harmonic generation (SHG) from bovine collagen-I fibrils. Using a stimulating pulse fluence of only 3 nJ/cm2, we obtain an SHG enhancement >10(4) relative to the spontaneous signal. The stimulation enhancement is greatest in situations where spontaneous signals are the weakest--such as low laser power, small sample volume, and weak nonlinear susceptibility--emphasizing the potential for this technique to improve signal-to-noise ratios in biological imaging and interfacial spectroscopy.
Subject(s)
Image Processing, Computer-Assisted/methods , Models, Theoretical , Optics and Photonics/methods , Signal Processing, Computer-Assisted , Image Processing, Computer-Assisted/instrumentation , Nonlinear Dynamics , Optics and Photonics/instrumentationABSTRACT
Semiconductor nanocrystals are called artificial atoms because of their atom-like discrete electronic structure resulting from quantum confinement. Artificial atoms can also be assembled into artificial molecules or solids, thus, extending the toolbox for material design. We address the interaction of artificial atoms with bulk semiconductor surfaces. These interfaces are model systems for understanding the coupling between localized and delocalized electronic structures. In many perceived applications, such as nanoelectronics, optoelectronics, and solar energy conversion, interfacing semiconductor nanocrystals to bulk materials is a key ingredient. Here, we apply the well established theories of chemisorption and interfacial electron transfer as conceptual frameworks for understanding the adsorption of semiconductor nanocrystals on surfaces, paying particular attention to instances when the nonadiabatic Marcus picture breaks down. We illustrate these issues using recent examples from our laboratory.
Subject(s)
Chemistry, Physical/methods , Electronics/methods , Models, Chemical , Quantum Dots , Semiconductors , Silicon/chemistry , Adsorption , Lead/chemistry , Microscopy, Electron, Scanning , Selenium Compounds/chemistry , Surface Properties , Titanium/chemistryABSTRACT
This paper examines the appropriateness of lay evaluations of potential risk of symptoms among a sample of 667 elderly people living in community settings. Data were gathered through personal interviews and 3 weeks of structured health diaries in which older respondents recorded the symptoms they experienced. Potential medical risk was determined on a symptom by symptom basis based on clinical information gathered during the interviews. Almost three fourths of the respondents exhibited potential clinical risk for at least one symptom they experienced during the 3-week diary period. One in eight respondents was judged at risk yet gave no evidence of physician consultation, either during or prior to the diary period. Implications of these results for health education designed to improve consultation decisions among elderly people are discussed.
Subject(s)
Decision Making , Geriatric Assessment , Health Status Indicators , Medical Records , Self Care , Aged , Aged, 80 and over , Data Collection , Female , Health Education , Humans , Information Services , Male , New York , Prevalence , Referral and Consultation/statistics & numerical data , Risk Factors , Rural Population , Sampling Studies , Self Care/psychology , Surveys and QuestionnairesABSTRACT
OBJECTIVES: To determine the prevalence and management of hearing loss and hearing handicap among non-demented nursing home residents. DESIGN: Descriptive study of total population of two nursing homes. PARTICIPANTS: All 121 eligible residents. SETTINGS: Two nursing homes. MINI OUTCOME MEASURES: Audiometry, questionnaires of nurses and subjects regarding perceived hearing handicap, and documentation in medical records of hearing loss. RESULTS: 77% had at least a mild (greater than or equal to 26 dB Hearing Level) hearing loss in the better ear, and 51% had a moderate to severe loss (greater than or equal to 41 dB HL). Self-assessments of hearing handicap by residents, together with audiometric findings and expressed interest in a hearing aid, were more useful guides for aural rehabilitation needs than were nurses' assessments of residents' handicaps. Medical records failed to identify 48% of residents with moderate to severe hearing losses. Fifty-eight percent of residents with severe hearing loss currently had hearing aids, and 38% more would like to have an aid. CONCLUSIONS: Residents should have hearing evaluations with documentation of results on admission and periodically under the direction of a nurse trained as a hearing specialist. Environmental modifications of the NH plus use of hearing aids can improve hearing.
