"… I seem […] only like a boy playing on the sea-shore, and diverting myself in now and then finding a smoother pebble or a prettier shell than ordinary, whilst the great ocean of truth lay all undiscovered before me". – Isaac Newton.
The electronegativity of a chemical element measures the tendency of an atom to attract electrons around it. This definition was formalized for the first time, in a semi-empirical form, by the chemist Linus Pauling in the early 1930s, but it had already been proposed in the late 1800s by the Swedish chemist Berzelius. In molecules, this tendency determines the molecular electronic distribution and therefore influences molecular properties such as the distribution of partial charges and chemical reactivity. Pauling provided an electronegativity scale by comparing bond dissociation energies of pairs of atoms (A, B) using the equation
With $E_{AB}$, $E_{AA}$, and $E_{BB}$ being the dissociation energies of the molecules AB, AA, and BB, respectively.
A few years later, in 1934, Mulliken proposed an expanded definition of electronegativity based on spectroscopically measurable atomic properties such as ionization potential (I) and electron affinity (E):
L’elettronegatività di un elemento chimico misura la tendenza di un atomo ad attrarre intorno a sé elettroni. Questa definizione fu formalizzata per la prima volta, in foma semi-empirica, dal chimico Linus Pauling all’inizio del 1930 ma era già stata proposta nella seconda metà dell’1800 dal chimico svedese Berzelius. Nelle molecole, questa tendenza determina la distribuzione elettronica molecolare e quindi influenza le proprietà molecolari quali per esempio, la distribuzione delle cariche parziali e la reattività chimica. Pauling ha fornito una scala di elettronegatività confrontando le energie di dissociazione di legame di coppie di atomi (A, B) usando la relazione
con , rispettivamente le energie di dissociazione delle molecole AB, AA, and BB.
Qualche anno dopo, nel 1934, Mulliken propose una definizione estesa di elettronegatività basata su proprietà atomiche misurabili spettroscopicamente, quali il potenziale di ionizzazione (I) e l’affinità elettronica (E):
What is the origin of the urge, the fascination that drives physicists, mathematicians, and presumably other scientists as well? Psychoanalysis suggests that it is sexual curiosity. You start by asking where little babies come from, one thing leads to another, and you find yourself preparing nitroglycerine or solving differential equations. This explanation is somewhat irritating, and therefore probably basically correct. David Ruelle, in Chance and Chaos
Here I am again for a new appointment with the Italian version of the column “Retro Programming Nostalgia“, my very own adventure in computer archaeology, rediscovering old programs written some time ago on microcomputers that have made their mark on an era.
This time, in my old floppy disks for the glorious Amiga 500, I found a program in Amiga Basic that I wrote during the early years of my university studies, when I was taking the course on differential equations II. Specifically, I was very fascinated by autonomous systems of differential equations due to their numerous applications in mathematical modeling of physical, chemical, and biological systems, as well as their importance in the theory of chaos. As in the series articles, I want to release an adapted version for the QB64 BASIC meta-compiler, but before presenting the program, I want to briefly explain what an autonomous system of differential equations is.
“Qual è l’origine del desiderio, della fascinazione che spinge i fisici, i matematici e presumibilmente anche altri scienziati? La psicoanalisi suggerisce che si tratti di curiosità sessuale. Si comincia chiedendosi da dove vengano i bambini piccoli, una cosa porta all’altra e ci si ritrova a preparare il nitroglicerina o a risolvere equazioni differenziali. Questa spiegazione è un po’ irritante, e quindi probabilmente fondamentalmente corretta.” – David Ruelle, in “Chance and Chaos”
Eccomi di nuovo per un nuovo appuntamento con la versione in italiano della Rubrica “Retro Programming Nostalgia “, la mia personalissima avventura d’ archeologia informatica alla riscoperta di vecchi programmi scritti qualche tempo fa su microcomputers che hanno segnato un’epoca.
Questa volta, nei miei vecchi dischetti per il glorioso Amiga 500, ho trovato un programma in Amiga Basic che scrissi durante i primi anni dei miei studi universitari, quando studiavo nel corso di matematica II, i sistemi d’equazioni differenziali. In particolare, ero molto affascinato dai sistemi di equazioni differenziali autonomi per via delle molteplici applicazioni nella modellazione matematica di sistemi fisici, chimici e biologici, e per la loro importanza nella teoria del caos. Come negli articoli della serie, voglio rilasciare una versione riadattata per il meta compilatore QB64 BASIC, ma prima di presentare il programma, voglio brevemente spiegare cosa sia un sistema autonomo di equazioni differenziali.
This article describes a new function of the LiStaLiA library. As I mentioned in Part I of this series of articles, I didn’t extensively test the library, so I am releasing it as an alpha version. Please let me know if you find any errors or if you improve the function, and feel free to send me your modified code!
CALCULATING STATISTICS PROPERTIES OF DATA SETS
The new functions perform a statistical analysis of the data set read by the function ReadData(). The source code of this new library functions is reported in the Appendix. The following list report all the descriptor calculated buy the functions.
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This is the second part of this series of notes on the advanced use of the Unix shell. The first part can be accessed by following the link. In this second part, I will show some advanced examples I wrote for my research activity.
1. CHANGE FILE NAMES SCRIPT
I wrote this script to change the default names of the files generated during a molecular dynamics simulation by the program mdrun in the early version of the GROMACS package for MD simulation. GROMACS is a widely used software package for simulating the behavior of molecules and molecular systems. Although it is now possible to define the root name of the files upon running the simulation program, this script can still be helpful. The script is written in the C Shell (csh) .
#! /bin/csh -ef
#
# Change the names of the default output Files
# generated by the program GROMACS mdrun program
#
# (c) Danilo Roccatano
#######
#
#Define the radix of the files name
#
setenv RADIX 'EH_min'
if (-e md.log) then
if ( -e $RADIX'.log') then
echo Warning $RADIX'.log' exist
else
mv md.log $RADIX'.log'
endif
else
echo The md.log file does not exist!
endif
if (-e ener.ene) then
if ( -e 'e'$RADIX'.ene') then
echo Warning 'e'$RADIX'.ene' exist
else
mv ener.ene 'e'$RADIX'.ene'
endif
else
echo The energy file does not exist
endif
if (-e ctraj.xtc ) then
if ( -e 'r'$RADIX'.xtc') then
echo Warning 'r'$RADIX'.xtc' exist
else
mv ctraj.xtc 'r'$RADIX'.xtc'
endif
else
echo The compressed trajectory file does not exist
endif
if (-e confout.gro) then
if ( -e 'x'$RADIX'.gro') then
echo Warning 'x'$RADIX'.gro' exist
else
mv confout.gro 'x'$RADIX'.gro'
endif
else
echo The final configuration file does not exit.
echo Probably your simulation crashed before the end
endif
exit
To grass, or leaf, or fruit, or wall, The snail sticks close, nor fears to fall, As if he grew there, house and all Together. Within that house secure he hides, When danger imminent betides Of storm, or other harm besides Of weather. Give but his horns the slightest touch, His self-collecting power is such, He shrinks into his house, with much Displeasure. Where’er he dwells, he dwells alone, Except himself has chattels none, Well satisfied to be his own Whole treasure. Thus, hermit-like, his life he leads, Nor partner of his banquet needs, And if he meets one, only feeds The faster. Who seeks him must be worse than blind, (He and his house are so combin’d) If, finding it, he fails to find Its master.
The Snail by William Cowper (1731-1800)
Introduzione
The beautiful poetry of Cowper expresses the pleasant charm that this small inhabitant of our gardens instills. I have always been fascinated by this gastropod, to the point that it was one of my favorite invertebrates for my amateur naturalistic observations. Furthermore, I still recall with pleasure and nostalgia the collection of those called ‘ciammaruchelle‘ in the Ciociaro dialect, which are small snails. These were gathered by the handful in the wheat fields after the harvest. It was one of the various culinary traditions that involved my entire family every year and were carried out with constant devotion. The collection was organized with careful timing, locations, and weather conditions to increase the likelihood of success. Usually, we would return home with a rich and tasty haul, but not without difficulties, as the little snails would climb onto the thistle plants (Cynara cardunculusL., 1753) where they would hide among the thorns to protect themselves from predators. Unfortunately for them, the predator Homo Sapiens Sapiens Frusinenses, equipped with keen eyesight and great tenacity, did not easily give up its prey!
The collected species was a variety of the snail Eobania vermiculata, commonly known as “rigatella,” which is very common in Mediterranean regions. The snails were gathered in woven baskets and, once back home, they were enclosed in circular cages with fine mesh walls for several days to purge their intestines. They were then cooked for a few hours in a tomato base spiced with mint (Clinopodium nepeta), following an ancient recipe. The dish was consumed with fresh or, even better, baked bread to make it crispy. It was a vibrant celebration of scents, flavors, and colors, with the sound of slurping as they tried to empty the succulent contents of their shells. A delicate feast of aromas and flavors: the scent of tomato infused with snail meat and mint, combined with the red color of the snails’ shells adorned with white-brown stripes.
In the recent Instructable project Introducing the Mini LED Table: Compact, Affordable, and Enhanced With Computer Vision, we presented an inexpensive, compact, and easy-to-build Mini LED Table (MLT) that is a simple and cost-effective project for a STEM activity and a tool for educational purposes. Among other applications, The device can open doors for students and educators to explore the fascinating world of material science and engineering by providing an affordable and compact solution.
In a new project on the Instructables website, I have extended the capability of the MLT by adding a device that uses polarizer filters in front of the Picamera, which will provide the capability to visualize the internal stress distribution within transparent materials. These stress patterns due to the birefringence of some materials are paramount for engineering analysis. They are significant in determining various substances’ mechanical behavior and structural integrity.
To address this possible application, we will explain how to add a polarizer to the MLT, which is already equipped with computer vision capabilities. In short, the accessory consists in adding a removable polarizer filter onto the Mini LED Table and incorporating another polarizer near the Picamera mounted on a rotatable 3D support enabling the visualization and analysis of colorful stress patterns that arise in transparent plastic and other materials exhibiting photoelastic effects.
By harnessing the capabilities of MLT, polarized light, and computer vision integration, we want to provide educators and students with a powerful tool for visualizing and understanding the intricate stress patterns present in transparent plastics and other photoelastic materials.
Before delving into the details of the project, let us provide a brief overview of photoelasticity and its significance in engineering. Photoelasticity is a powerful technique used to analyze the stress distribution in materials. It is based on the principle that the refractive index of a photoelastic material changes with applied stress. By passing polarized light through a stressed material and analyzing the resulting fringe patterns, engineers can gain valuable insights into the stress distribution and behavior of the material under various loading conditions.
Photoelasticity finds extensive applications in engineering. It aids in designing and analyzing components subjected to complex stress states, such as structural components, machine parts, and even optical devices. By visualizing stress concentrations, engineers can optimize designs, identify potential failure points, and enhance various systems’ overall reliability and performance. Additionally, photoelasticity plays a crucial role in material testing, prototype validation, and quality control processes, enabling engineers to ensure the integrity and safety of critical components.
, rispettivamente le energie di dissociazione delle molecole AB, AA, and BB.
