Physics: Energy and Momentum Concepts

Kinetic Energy

• Kinetic energy is the amount of work an object can perform when its speed is reduced to zero.
• Formula: KE = 1/2 * m * v²
• Unit: Joule

Electron Volt (eV)

• Electron volt is a unit of energy.
• Equivalent to the kinetic energy gained by an electron accelerated through a 1V potential difference.

Force

• Force is a vector quantity.
• Characterizes the ability to cause acceleration.

Momentum

• Momentum is a vector quantity.
• Product of mass and velocity: p = m * v

Electromagnetic Spectrum

• Electromagnetic spectrum components, in ascending energy order:
  • Radiowaves
  • Microwaves
  • Infrared
  • Visible light
  • Ultraviolet
  • X-rays
  • Gamma rays

Visible Light

• Range of electromagnetic radiation detectable by the human eye (approximately 400-750 nm).

Limiting Frequency (fmax)

• Maximum frequency of braking radiation.
• Formula: fmax = eU/h, where U is voltage, e is charge of electron and h is Planck's constant.

X-ray Absorption Mechanisms

• Three primary mechanisms:
  • Photoelectric effect
  • Compton effect
  • Pair production

Photoelectric vs Compton Effect

• Photoelectric effect: X-ray energy is used to ionize the atom and give kinetic energy to the electron.
• Compton effect: Only part of the photon's energy is used for electron emission, the rest is scattered.

Laser Light Characteristics

• Monochromatic
• Coherent (in time and space)
• Low divergence
• High intensity

Laser-Tissue Interactions

• Photothermal (thermy, coagulation, vaporization, carbonization)
• Fluorescence/photochemical reactions
• Photodissociation
• Multiphoton ionization

Light Intensity and Absorbance

• 10-fold decrease in intensity for each unit increase in absorbance.

Molar Extinction Coefficient

• Absorbance of a 1M solution with a 1cm path length.

Protein/Nucleic Acid Absorption

• Characteristic absorption maxima:
  • Proteins (280 nm)
  • Nucleic acids (260 nm)

Amino Acids with High Absorption

• Tyrosine (Tyr)
• Tryptophan (Trp)
• Phenylalanine (Phe)

Singlet and Triplet States

• Singlet state: zero unpaired electrons. Spin multiplicity = 1.
• Triplet state: two unpaired electrons. Spin multiplicity = 3.

Excited Electronic State Relaxation in Molecules

• Vibrational relaxation
• Internal conversion
• Intersystem crossing
• Fluorescence
• Phosphorescence
• Delayed fluorescence
• Energy transfer

Fluorescence Lifetime

• Time required for the number of excited molecules to decrease to 1/e (approximately 37%) of initial value.

Scintillation, Chemiluminescence, Photoluminescence

• Scintillation: photon emission due to ionizing radiation.
• Chemiluminescence: photon emission due to a chemical reaction.
• Photoluminescence: photon emission due to excitation by photons.

Fluorescent Measurements

• DNA, RNA, protein, and lipid content of a cell
• Membrane permeability
• Intracellular enzymes
• Membrane potential
• Intracellular calcium level
• Intracellular pH

Shortest Resolvable Distance (Light Microscope)

• Approximately 200 nm

Isotopes

• Variants of an element with same atomic number but different mass numbers.

Nucleon Energy Levels

• Nucleons in nuclei reside at lower energy levels compared to free particles.

Radioactive Decay: Atomic Number and Mass Number Changes

• Decay types and associated changes in atomic and mass numbers tabulated.

Radioactive Decay Equation

• Equation describing the number of undecayed radioactive nuclei over time (N=Noe^(-λt)).

Effective, Physical, Biological Half-lives

• Interrelation formula provided.

Ionizing Radiations

• Alpha and beta- radiations are directly ionizing due to their charge.

GM-Counter Detection

• Detects alpha, beta, and gamma particles

Scintillation Detector Detection

• Converts radioactive particle energy to luminous energy (light flashes).

Radioactive Radiation Penetrability

• Alpha < Beta < Gamma

Biological Effects of Irradiation

• D37 (dose required for 37% survival)
• Radiations damage in aqueous solutions

Effective Dose

• Weighted sum of equivalent doses in different tissues/organs
• Used because radiation sensitivity differs among tissues

Factors Determining Radiation Sensitivity

• Radiation quality
• Time factor
• Temperature
• Oxygen effect
• Protective substances

Cell Survival Model (Linear-Quadratic)

• Equation modeling cell survival with dose.

Cell Cycle Radiosensitivity

• Cells most sensitive during mitosis and most resistant during late S phase.

SPECT

• Images taken from different directions using a gamma camera.
• Used to determine distribution of radioactive source.

SPECT Isotopes

• Nuclei used in the SPECT process.

Computer Tomography

• X-ray images from multiple directions to determine 3D structure.

NMR Active Nuclei

• Nuclei with non-zero nuclear spin.

Biological Applications of NMR

• Nuclei used for biological applications.

Macroscopic Magnetic Field Consequence

• When nuclei's magnetic moments are aligned with an external field, macroscopic magnetization occurs (either equilibrium/longitudinal).

MRI Image Parameters

• Reveals 1H nuclei density and relaxation rates.

In Vivo MRS

• Non-invasive technique to show metabolic processes in living tissue using NMR spectroscopy.

Ultrasonic Frequency Range

• Audibly detectable sound frequencies for humans.

Sound Intensity Definition

• Rate of sound energy traveling through unit area.

Medium Compressibility

• Change in volume relative to pressure increase.

Ultrasound Generation Method

• Methods applicable for ultrasound generation.

Frictional Force (in aqueous environment)

• Force acting on a molecule due to friction in an environment.
• Formula: Fr=-fv

Diffusion Constant

• Physical quantity representing diffusion.
• Units (m²/s).

Fick's First Law

• Law describing concentration-driven material transfer.
• Constants and interpretation provided.

Diffusion Equilibrium Factors

• Parameters that tend to equilibrium in diffusion.
• Example: Chemical potentials.

Osmotic Pressure

• Pressure that prevents solvent flow into a solution.

Lipid Membrane Motion Forms

• Lipid movement in cellular membranes.
• Examples: Lateral diffusion, rotational diffusion, membrane flip-flop.

Membrane Properties Changes

• Factors impacting membrane transition temperature.
• Example: Fatty acid saturation, chain length.

Membrane Permeability

• Permeability for apolar and other molecules

Extra/Intracellular Ion Concentrations

• Concentrations for key ions listed.

Facilitated Diffusion

• Passive transport aided by transport proteins.

Ion Channel Activation

• Categorization based on activation mechanisms.

Ionophores

• Grouping based on ion transport mechanisms

Resting Membrane Potential Maintenance

• Factors contributing to maintenance of membrane's resting potential.

Equilibrium Potential

• Membrane potential where net flux of a given ion is zero (thermodynamic equilibrium).

Goldman-Hodgkin-Katz Equation

• Equation relating resting membrane potential to ion permeabilities and concentrations.

Eye Resolution

• Smallest visual angle for distinguishing two points.

Photoreceptor Triggering

• Photons trigger receptor chemical processes.

Phon Scale vs Bel Scale

• Phon scale uses normalized intensity of 1000Hz sound to evaluate loudness.

Weber-Fechner Law

• Sensation intensity relation to stimulus log ratio.

Isophonic Curves

• Representation of sound intensity and frequency for same loudness sensation.

Hearing Mechanism (Air Conduction)

• Mechanism description for hearing from outer to inner ear via ossicles.

Bone Anisotropy

• Resistance to mechanical stress varies with force's direction.

Fluid Continuity Equation

• Relation between flow rate and cross-sectional areas (in fluid dynamics).

Hagen-Poiseuille Law

• Equation relating volumetric flow rate, pressure gradient, and viscosity.

Lung Compliance Factors

• Factors determining lung compliance.
• Example: Tissue elastic recoil and surface tension

Surface Tension

• Work needed to increase a liquid's surface area

Atomic Force Microscopy Resolution

• Resolution limit for atomic-level imaging.

Sedimentation Constant

• Sedimentation velocity under unit acceleration.
• Units (Svedberg).

Electrophoretic Mobility

• Velocity of a particle in electric field.