Report on a User Test and Extension of a Type Debugger for Novice Programmers

A type debugger interactively detects the expressions that cause type errors. It asks users whether they intend the types of identifiers to be those that the compiler inferred. However, it seems that novice programmers often get in trouble when they think about how to fix type errors by reading the messages given by the type debugger. In this paper, we analyze the user tests of a type debugger and report problems of the current type debugger. We then extend the type debugger to address these problems. Specifically, we introduce expression-specific error messages and language levels. Finally, we show type errors that we think are difficult to explain to novice programmers. The subjects of the user tests were 40 novice students belonging to the department of information science at Ochanomizu University.Comment: In Proceedings TFPIE 2014, arXiv:1412.473

A Functional Abstraction of Typed Invocation Contexts

In their paper "A Functional Abstraction of Typed Contexts", Danvy and Filinski show how to derive a monomorphic type system of the shift and reset operators from a CPS semantics. In this paper, we show how this method scales to Felleisen's control and prompt operators. Compared to shift and reset, control and prompt exhibit a more dynamic behavior, in that they can manipulate a trail of contexts surrounding the invocation of previously captured continuations. Our key observation is that, by adopting a functional representation of trails in the CPS semantics, we can derive a type system that encodes all and only constraints imposed by the CPS semantics

Direct implementation of shift and reset in the MinCaml compiler

Although delimited control operators are becoming one of the useful tools to manipulate flow of programs, their direct and compiled implementation in a low-level language has not been proposed so far. The only direct and low-level implementations available are Gasbichler and Sperber’s implementation in the Scheme 48 virtual machine and Kiselyov’s implementation in the OCaml bytecode. Even though these implementations do provide an insight into how stack frames are composed, they are not directly portable to compiled implementation at the assembly language. This paper presents a direct implementation of delimited control operators shift and reset in the MinCaml compiler. It shows all the details of how composable continuations can be implemented in the PowerPC microprocessor using the stack strategy. We also show an implementation that copies the stack frames lazily. To our knowledge, this is the first implementation of shift/reset in the assembly language. It makes clear at the assembly language level what we have informally described so far, such as “copying and composing stack frames ” and “inserting a reset mark when captured continuations are called”. We demonstrate various benchmarks to show the performance of the direct implementation and discuss its pros and cons.

Direction Detector on an Excitable Field: Field Computation with Coincidence Detection

Living organisms process information without any central control unit and without any ruling clock. We have been studying a novel computational strategy that uses a geometrically arranged excitable field, i.e., "field computation." As an extension of this research, in the present article we report the construction of a "direction detector" on an excitable field. Using a numerical simulation, we show that the direction of a input source signal can be detected by applying the characteristic as a "coincidence detector" embedded on an excitable field. In addition, we show that this direction detection actually works in an experiment using an excitable chemical system. These results are discussed in relation to the future development of "field computation."Comment: 6 pages, 3 figure

Tracking the Evolution and Diversity in Network Usage of Smartphones

ABSTRACT We analyze the evolution of smartphone usage from a dataset obtained from three, 15-day-long, user-side, measurements with over 1500 recruited smartphone users in the Greater Tokyo area from 2013 to 2015. This dataset shows users across a diverse range of networks; cellular access (3G to LTE), WiFi access (2.4 to 5GHz), deployment of more public WiFi access points (APs), as they use diverse applications such as video, file synchronization, and major software updates. Our analysis shows that smartphone users select appropriate network interfaces taking into account the deployment of emerging technologies, their bandwidth demand, and their economic constraints. Thus, users show diversity in both how much traffic they send, as well as on what networks they send it. We show that users are gradually but steadily adopting WiFi at home, in offices, and public spaces over these three years. The majority of light users have been shifting their traffic to WiFi. Heavy hitters acquire more bandwidth via WiFi, especially at home. The percentage of users explicitly turning off their WiFi interface during the day decreases from 50% to 40%. Our results highlight that the offloading environment has been improved during the three years, with more than 40% of WiFi users connecting to multiple WiFi APs in one day. WiFi offload at offices is still limited in our dataset due to a few accessible APs, but WiFi APs in public spaces have been an alternative to cellular access for users who request not only simple connectivity but also bandwidth-consuming applications such as video streaming and software updates. Categories and Subject Descriptors General Terms Measurement Permission to make digital or hard copies of all or part of this work for personal or classroom use is granted without fee provided that copies are not made or distributed for profit or commercial advantage and that copies bear this notice and the full citation on the first page. Copyrights for components of this work owned by others than the author(s) must be honored. Abstracting with credit is permitted. To copy otherwise, or republish, to post on servers or to redistribute to lists, requires prior specific permission and/or a fee. Request permissions from [email protected]

Thermodynamic properties of small flares in the quiet Sun observed by Hα\alpha and EUV: plasma motion of the chromosphere and time evolution of temperature/emission measure

Small flares frequently occur in the quiet Sun. Previous studies have noted that they share many common characteristics with typical solar flares in active regions. However, their similarities and differences are not fully understood, especially their thermal properties. In this study, we performed imaging spectroscopic observations in the H$\alpha$ line taken with the Solar Dynamics Doppler Imager on the Solar Magnetic Activity Research Telescope (SMART/SDDI) at the Hida Observatory and imaging observations with the Atmospheric Imaging Assembly onboard Solar Dynamics Observatory (SDO/AIA). We analysed 25 cases of small flares in the quiet Sun over the thermal energy range of $10^{24}-10^{27}\,\mathrm{erg}$, paying particular attention to their thermal properties. Our main results are as follows: (1) We observe a redshift together with line centre brightening in the H$\alpha$ line associated with more than half of the small flares. (2) We employ differential emission measure analysis using AIA multi-temperature (channel) observations to obtain the emission measure and temperature of the small flares. The results are consistent with the Shibata & Yokoyama (1999, 2002) scaling law. From the scaling law, we estimated the coronal magnetic field strength of small flares to be 5 --15 G. (3) The temporal evolution of the temperature and the density shows that the temperature peaks precede the density peaks in more than half of the events. These results suggest that chromospheric evaporations/condensations play an essential role in the thermal properties of some of the small flares in the quiet Sun, as does for large flares.Comment: 14 pages, 12 figures, accepted for publication in MNRA

Unified Relationship between Cold Plasma Ejections and Flare Energies Ranging from Solar Microflares to Giant Stellar Flares

We often find spectral signatures of chromospheric cold plasma ejections accompanied by flares in a wide range of spatial scales in the solar and stellar atmospheres. However, the relationship between physical quantities (such as mass, kinetic energy, and velocity) of cold ejecta and flare energy has not been investigated in a unified manner for the entire range of flare energies to date. This study analyzed the spectra of cold plasma ejections associated with small-scale flares and solar flares (energy $10^{25}-10^{29}\,\mathrm{erg}$) to supply smaller energy samples. We performed H$\alpha$ imaging spectroscopy observation by the Solar Dynamics Doppler Imager on the Solar Magnetic Activity Research Telescope (SMART/SDDI). We determined the physical quantities of the ejecta by cloud model fitting to the H$\alpha$ spectrum. We determined flare energy by differential emission measure analysis using Atmospheric Imaging Assembly onboard Solar Dynamics Observatory (SDO/AIA) for small-scale flares and by estimating the bolometric energy for large-scale flares. As a result, we found that the ejection mass $M$ and the total flare energy $E_{\mathrm{tot}}$ follow a relation of $M\propto E_{\mathrm{tot}}^{2/3}$. We show that the scaling law derived from a simple physical model explains the solar and stellar observations with a coronal magnetic field strength as a free parameter. We also found that the kinetic energy and velocity of the ejecta correlate with the flare energy. These results suggest a common mechanism driven by magnetic fields to cause cold plasma ejections with flares on the Sun and stars.Comment: 23 pages, 10 figures; accepted for publication in Ap

Precise measurement of positronium hyperfine splitting using the Zeeman effect

Positronium is an ideal system for the research of the quantum electrodynamics (QED) in bound state. The hyperfine splitting (HFS) of positronium, $\Delta_{\mathrm{HFS}}$, gives a good test of the bound state calculations and probes new physics beyond the Standard Model. A new method of QED calculations has revealed the discrepancy by 15\,ppm (3.9$\sigma$) of $\Delta_{\mathrm{HFS}}$ between the QED prediction and the experimental average. There would be possibility of new physics or common systematic uncertainties in the previous all experiments. We describe a new experiment to reduce possible systematic uncertainties and will provide an independent check of the discrepancy. We are now taking data and the current result of $\Delta_{\mathrm{HFS}} = 203.395\,1 \pm 0.002\,4 (\mathrm{stat.}, 12\,\mathrm{ppm}) \pm 0.001\,9 (\mathrm{sys.}, 9.5\,\mathrm{ppm})\,\mathrm{GHz}$ has been obtained so far. A measurement with a precision of $O$(ppm) is expected within a year.Comment: 8 pages, 8 figures, 2 tables, proceeding of LEAP2011, accepted by Hyperfine Interaction