Methodology Article
The Laser-drop-method: Making Microorganisms Visible Without a Microscope Using a Simple Laser Pointer
Andreas Korn-Mueller*
Issue:
Volume 11, Issue 1, March 2026
Pages:
1-6
Received:
10 January 2026
Accepted:
29 January 2026
Published:
9 February 2026
Abstract: In order to get students and the general public excited about physics and biology, you need experiments that are as simple and exciting as possible. They should be interesting but also inexpensive to promote interest in scientific experimentation. A drop of water acts like a magnifying glass, allowing you to see particles trapped inside it. All you need is a usual red or green laser pointer and a plastic syringe. Simply draw the water to be examined into the syringe and squeeze out a drop that just hangs from the tip of the syringe. By simply shining a laser beam through a drop of water hanging from the tip of the syringe, the particles are cast as magnified shadows on any wall (screen). This ‘laser drop method’ can be used to examine, view and measure microorganisms and green algae from ponds, pools and lakes. Even oral mucosa cells from the mouth and hairs can be magnified and made visible using the ‘laser drop method’. In addition, all zooplankton can be observed in the water droplets as very agile and free-swimming organisms. This method is very simple and a low-cost science activity, and is suitable for outdoor excursions, in lecture halls for students and in the classroom of higher grades as well as for demonstrations to the general public, as a tool of applied physics and biology. Home experimentation is also possible with the ‘laser drop method’.
Abstract: In order to get students and the general public excited about physics and biology, you need experiments that are as simple and exciting as possible. They should be interesting but also inexpensive to promote interest in scientific experimentation. A drop of water acts like a magnifying glass, allowing you to see particles trapped inside it. All you...
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Research Article
On the Reduction of Classical Spin in One-dimensional Heisenberg Magnets with Spin S>1/2
Farhod Rahimi*
Issue:
Volume 11, Issue 1, March 2026
Pages:
7-15
Received:
5 February 2026
Accepted:
14 February 2026
Published:
27 February 2026
Abstract: This paper develops a semiclassical framework for one-dimensional Heisenberg magnets with spin S>1/2, where classical approaches are reliable only as S→∞ and can miss quantum contributions from multipole moments. The aim is to construct a workable mathematical apparatus that connects the quantum lattice Hamiltonian to an effective classical field description while incorporating an effective reduction of the classical spin length. The analysis starts from an anisotropic Heisenberg chain with nearest-neighbour exchange and single-ion anisotropy. After outlining the continuum (long-wavelength) reduction, including factorization of slowly varying fields and replacement of commutators by Poisson brackets, the semiclassical limit is formulated using a Hartree product ansatz and generalized SU(N) coherent states for each lattice site. For spin S=1 the coherent state is built on the SU(3)/[SU(2)×U(1)] manifold. Two Euler angles define the orientation of the classical spin vector, an additional angle describes rotation of the quadrupole tensor about this vector, and a real parameter g controls the redistribution between dipolar and quadrupolar sectors. Averaging the spin operators yields explicit classical components and shows that the standard constraint |S|^2=1 is violated. Instead, an identity relates the reduced spin length to a combination of double correlators, demonstrating that quadrupolar degrees of freedom quantitatively produce a measurable renormalization of the effective classical spin. For spin S=3/2 the construction is generalized to SU(4) coherent states, where both quadrupole and octupole moments arise naturally. The averaged spin operators again violate spin-length conservation and, moreover, simple projection sum rules. The corresponding SU(4) identities involve combinations of triple correlators and introduce parameters g and k that quantify reductions due to quadrupolar and octupolar sectors, respectively; the SU(3) case is recovered when k=0. The framework provides a transparent route to include multipolar physics in semiclassical dynamics and is relevant for interpreting nonlinear collective excitations, including soliton-like modes, in quantum spin chains.
Abstract: This paper develops a semiclassical framework for one-dimensional Heisenberg magnets with spin S>1/2, where classical approaches are reliable only as S→∞ and can miss quantum contributions from multipole moments. The aim is to construct a workable mathematical apparatus that connects the quantum lattice Hamiltonian to an effective classical field d...
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