Advances in atomic force microscopy

This article reviews the progress of atomic force microscopy (AFM) in ultra-high vacuum, starting with its invention and covering most of the recent developments. Today, dynamic force microscopy allows to image surfaces of conductors \emph{and} insulators in vacuum with atomic resolution. The mostly used technique for atomic resolution AFM in vacuum is frequency modulation AFM (FM-AFM). This technique, as well as other dynamic AFM methods, are explained in detail in this article. In the last few years many groups have expanded the empirical knowledge and deepened the theoretical understanding of FM-AFM. Consequently, the spatial resolution and ease of use have been increased dramatically. Vacuum AFM opens up new classes of experiments, ranging from imaging of insulators with true atomic resolution to the measurement of forces between individual atoms.Comment: In press (Reviews of Modern Physics, scheduled for July 2003), 86 pages, 44 figure

Jahn-Teller effect in the magnesium phthalocyanine anion

We present an ab initio study of the static Jahn\u2013Teller (JT) effect in the magnesium phthalocyanine anion (MgPc 12). The neutral MgPc has D4h symmetry with a doubly degenerate eg affinity level and 14 B1g plus 14 B2g JT active modes. MgPc 12 is thus a physical realization of a eg 97 (B1g 95 B2g) JT problem. We carried out a first principles DFT/LDA calculation of the electronic structure, full vibrational spectrum, and linear electron\u2013vibration coupling constants for this system. From that we calculate a static JT energy gain of 50 meV \u2013 essentially due to a B1g distortion \u2013 characterizing this as a relatively weak-coupling system. It is anticipated that quantum mechanical dynamic JT tunneling between the two equivalent B1g distorted JT minima should be quite important. Two B2g distorted saddle points are identified as the relevant transition states, with a barrier of 27 meV above the minima. Previous work on this JT problem is also addressed

Organic molecular crystals in electric fields

We present ab initio density functional (DFT) calculations of the electronic properties of organic molecular crystals surfaces in an electric field. We investigate the electronic structure of small slabs of benzene (six layers) and anthracene (four layers) and study their changes due to electric fields perpendicular to the slab surfaces. For extreme fields, charge transfer between the two surfaces could occur in the simulation. We found that benzene and anthracene show a different behavior due to the different electron affinity. While in anthracene two charged layers form at the two surfaces, one of electron type and the other of hole type, electrons from benzene slab are pulled out to vacuum due to negligible or negative electron affinit

Patient Interactions With an Automated Conversational Agent Delivering Pretest Genetics Education: Descriptive Study

BackgroundCancer genetic testing to assess an individual’s cancer risk and to enable genomics-informed cancer treatment has grown exponentially in the past decade. Because of this continued growth and a shortage of health care workers, there is a need for automated strategies that provide high-quality genetics services to patients to reduce the clinical demand for genetics providers. Conversational agents have shown promise in managing mental health, pain, and other chronic conditions and are increasingly being used in cancer genetic services. However, research on how patients interact with these agents to satisfy their information needs is limited. ObjectiveOur primary aim is to assess user interactions with a conversational agent for pretest genetics education. MethodsWe conducted a feasibility study of user interactions with a conversational agent who delivers pretest genetics education to primary care patients without cancer who are eligible for cancer genetic evaluation. The conversational agent provided scripted content similar to that delivered in a pretest genetic counseling visit for cancer genetic testing. Outside of a core set of information delivered to all patients, users were able to navigate within the chat to request additional content in their areas of interest. An artificial intelligence–based preprogrammed library was also established to allow users to ask open-ended questions to the conversational agent. Transcripts of the interactions were recorded. Here, we describe the information selected, time spent to complete the chat, and use of the open-ended question feature. Descriptive statistics were used for quantitative measures, and thematic analyses were used for qualitative responses. ResultsWe invited 103 patients to participate, of which 88.3% (91/103) were offered access to the conversational agent, 39% (36/91) started the chat, and 32% (30/91) completed the chat. Most users who completed the chat indicated that they wanted to continue with genetic testing (21/30, 70%), few were unsure (9/30, 30%), and no patient declined to move forward with testing. Those who decided to test spent an average of 10 (SD 2.57) minutes on the chat, selected an average of 1.87 (SD 1.2) additional pieces of information, and generally did not ask open-ended questions. Those who were unsure spent 4 more minutes on average (mean 14.1, SD 7.41; P=.03) on the chat, selected an average of 3.67 (SD 2.9) additional pieces of information, and asked at least one open-ended question. ConclusionsThe pretest chat provided enough information for most patients to decide on cancer genetic testing, as indicated by the small number of open-ended questions. A subset of participants were still unsure about receiving genetic testing and may require additional education or interpersonal support before making a testing decision. Conversational agents have the potential to become a scalable alternative for pretest genetics education, reducing the clinical demand on genetics providers